<!-- $PostgreSQL: pgsql/doc/src/sgml/ecpg.sgml,v 1.100 2010/05/13 14:16:41 mha Exp $ -->

<chapter id="ecpg">
 <title><application>ECPG</application> - Embedded <acronym>SQL</acronym> in C</title>

 <indexterm zone="ecpg"><primary>embedded SQL</primary><secondary>in C</secondary></indexterm>
 <indexterm zone="ecpg"><primary>C</primary></indexterm>
 <indexterm zone="ecpg"><primary>ECPG</primary></indexterm>

 <para>
  This chapter describes the embedded <acronym>SQL</acronym> package
  for <productname>PostgreSQL</productname>. It was written by
  Linus Tolke (<email>linus@epact.se</email>) and Michael Meskes
  (<email>meskes@postgresql.org</email>). Originally it was written to work with
  <acronym>C</acronym>. It also works with <acronym>C++</acronym>, but
  it does not recognize all <acronym>C++</acronym> constructs yet. 
 </para>

 <para>
  This documentation is quite incomplete.  But since this
  interface is standardized, additional information can be found in
  many resources about SQL.
 </para>

 <sect1 id="ecpg-concept">
  <title>The Concept</title>

  <para>
   An embedded SQL program consists of code written in an ordinary
   programming language, in this case C, mixed with SQL commands in
   specially marked sections.  To build the program, the source code
   is first passed through the embedded SQL preprocessor, which converts it
   to an ordinary C program, and afterwards it can be processed by a C
   compiler.
  </para>

  <para>
   Embedded <acronym>SQL</acronym> has advantages over other methods
   for handling <acronym>SQL</acronym> commands from C code. First, it
   takes care of the tedious passing of information to and from
   variables in your <acronym>C</acronym> program.  Second, the SQL
   code in the program is checked at build time for syntactical
   correctness.  Third, embedded <acronym>SQL</acronym> in C is
   specified in the <acronym>SQL</acronym> standard and supported by
   many other <acronym>SQL</acronym> database systems.  The
   <productname>PostgreSQL</> implementation is designed to match this
   standard as much as possible, and it is usually possible to port
   embedded <acronym>SQL</acronym> programs written for other SQL
   databases to <productname>PostgreSQL</productname> with relative
   ease.
  </para>

  <para>
   As already stated, programs written for the embedded
   <acronym>SQL</acronym> interface are normal C programs with special
   code inserted to perform database-related actions.  This special
   code always has the form:
<programlisting>
EXEC SQL ...;
</programlisting>
   These statements syntactically take the place of a C statement.
   Depending on the particular statement, they can appear at the
   global level or within a function.  Embedded
   <acronym>SQL</acronym> statements follow the case-sensitivity rules
   of normal <acronym>SQL</acronym> code, and not those of C.
  </para>

  <para>
   The following sections explain all the embedded SQL statements.
  </para>
 </sect1>

 <sect1 id="ecpg-connect">
  <title>Connecting to the Database Server</title>

  <para>
   One connects to a database using the following statement:
<programlisting>
EXEC SQL CONNECT TO <replaceable>target</replaceable> <optional>AS <replaceable>connection-name</replaceable></optional> <optional>USER <replaceable>user-name</replaceable></optional>;
</programlisting>
   The <replaceable>target</replaceable> can be specified in the
   following ways:

   <itemizedlist>
    <listitem>
     <simpara>
      <literal><replaceable>dbname</><optional>@<replaceable>hostname</></optional><optional>:<replaceable>port</></optional></literal>
     </simpara>
    </listitem>

    <listitem>
     <simpara>
      <literal>tcp:postgresql://<replaceable>hostname</><optional>:<replaceable>port</></optional><optional>/<replaceable>dbname</></optional><optional>?<replaceable>options</></optional></literal>
     </simpara>
    </listitem>

    <listitem>
     <simpara>
      <literal>unix:postgresql://<replaceable>hostname</><optional>:<replaceable>port</></optional><optional>/<replaceable>dbname</></optional><optional>?<replaceable>options</></optional></literal>
     </simpara>
    </listitem>
 
    <listitem>
     <simpara>
      an SQL string literal containing one of the above forms
     </simpara>
    </listitem>

    <listitem>
     <simpara>
      a reference to a character variable containing one of the above forms (see examples)
     </simpara>
    </listitem>
 
    <listitem>
     <simpara>
      <literal>DEFAULT</literal>
     </simpara>
    </listitem>
   </itemizedlist>

   If you specify the connection target literally (that is, not
   through a variable reference) and you don't quote the value, then
   the case-insensitivity rules of normal SQL are applied.  In that
   case you can also double-quote the individual parameters separately
   as needed.  In practice, it is probably less error-prone to use a
   (single-quoted) string literal or a variable reference.  The
   connection target <literal>DEFAULT</literal> initiates a connection
   to the default database under the default user name.  No separate
   user name or connection name can be specified in that case.
  </para>

  <para>
   There are also different ways to specify the user name:

   <itemizedlist>
    <listitem>
     <simpara>
      <literal><replaceable>username</replaceable></literal>
     </simpara>
    </listitem>

    <listitem>
     <simpara>
      <literal><replaceable>username</replaceable>/<replaceable>password</replaceable></literal>
     </simpara>
    </listitem>

    <listitem>
     <simpara>
      <literal><replaceable>username</replaceable> IDENTIFIED BY <replaceable>password</replaceable></literal>
     </simpara>
    </listitem>

    <listitem>
     <simpara>
      <literal><replaceable>username</replaceable> USING <replaceable>password</replaceable></literal>
     </simpara>
    </listitem>
   </itemizedlist>

   As above, the parameters <replaceable>username</replaceable> and
   <replaceable>password</replaceable> can be an SQL identifier, an
   SQL string literal, or a reference to a character variable.
  </para>

  <para>
   The <replaceable>connection-name</replaceable> is used to handle
   multiple connections in one program.  It can be omitted if a
   program uses only one connection.  The most recently opened
   connection becomes the current connection, which is used by default
   when an SQL statement is to be executed (see later in this
   chapter).
  </para>

  <para>
   Here are some examples of <command>CONNECT</command> statements:
<programlisting>
EXEC SQL CONNECT TO mydb@sql.mydomain.com;

EXEC SQL CONNECT TO unix:postgresql://sql.mydomain.com/mydb AS myconnection USER john;

EXEC SQL BEGIN DECLARE SECTION;
const char *target = "mydb@sql.mydomain.com";
const char *user = "john";
EXEC SQL END DECLARE SECTION;
 ...
EXEC SQL CONNECT TO :target USER :user;
</programlisting>
   The last form makes use of the variant referred to above as
   character variable reference.  You will see in later sections how C
   variables can be used in SQL statements when you prefix them with a
   colon.
  </para>

  <para>
   Be advised that the format of the connection target is not
   specified in the SQL standard.  So if you want to develop portable
   applications, you might want to use something based on the last
   example above to encapsulate the connection target string
   somewhere.
  </para>
 </sect1>

 <sect1 id="ecpg-disconnect">
  <title>Closing a Connection</title>

  <para>
   To close a connection, use the following statement:
<programlisting>
EXEC SQL DISCONNECT <optional><replaceable>connection</replaceable></optional>;
</programlisting>
   The <replaceable>connection</replaceable> can be specified
   in the following ways:

   <itemizedlist>
    <listitem>
     <simpara>
      <literal><replaceable>connection-name</replaceable></literal>
     </simpara>
    </listitem>

    <listitem>
     <simpara>
      <literal>DEFAULT</literal>
     </simpara>
    </listitem>

    <listitem>
     <simpara>
      <literal>CURRENT</literal>
     </simpara>
    </listitem>

    <listitem>
     <simpara>
      <literal>ALL</literal>
     </simpara>
    </listitem>
   </itemizedlist>

   If no connection name is specified, the current connection is
   closed.
  </para>

  <para>
   It is good style that an application always explicitly disconnect
   from every connection it opened.
  </para>
 </sect1>

 <sect1 id="ecpg-commands">
  <title>Running SQL Commands</title>

  <para>
   Any SQL command can be run from within an embedded SQL application.
   Below are some examples of how to do that.
  </para>

  <para>
   Creating a table:
<programlisting>
EXEC SQL CREATE TABLE foo (number integer, ascii char(16));
EXEC SQL CREATE UNIQUE INDEX num1 ON foo(number);
EXEC SQL COMMIT;
</programlisting>
  </para>

  <para>
   Inserting rows:
<programlisting>
EXEC SQL INSERT INTO foo (number, ascii) VALUES (9999, 'doodad');
EXEC SQL COMMIT;
</programlisting>
  </para>

  <para>
   Deleting rows:
<programlisting>
EXEC SQL DELETE FROM foo WHERE number = 9999;
EXEC SQL COMMIT;
</programlisting>
  </para>

  <para>
   Single-row select:
<programlisting>
EXEC SQL SELECT foo INTO :FooBar FROM table1 WHERE ascii = 'doodad';
</programlisting>
  </para>

  <para>
   Select using cursors:
<programlisting>
EXEC SQL DECLARE foo_bar CURSOR FOR
    SELECT number, ascii FROM foo
    ORDER BY ascii;
EXEC SQL OPEN foo_bar;
EXEC SQL FETCH foo_bar INTO :FooBar, DooDad;
...
EXEC SQL CLOSE foo_bar;
EXEC SQL COMMIT;
</programlisting>
  </para>

  <para>
   Updates:
<programlisting>
EXEC SQL UPDATE foo
    SET ascii = 'foobar'
    WHERE number = 9999;
EXEC SQL COMMIT;
</programlisting>
  </para>

  <para>
   The tokens of the form
   <literal>:<replaceable>something</replaceable></literal> are
   <firstterm>host variables</firstterm>, that is, they refer to
   variables in the C program.  They are explained in <xref
   linkend="ecpg-variables">.
  </para>

  <para>
   In the default mode, statements are committed only when
   <command>EXEC SQL COMMIT</command> is issued. The embedded SQL
   interface also supports autocommit of transactions (similar to
   <application>libpq</> behavior) via the <option>-t</option> command-line
   option to <command>ecpg</command> (see below) or via the <literal>EXEC SQL
   SET AUTOCOMMIT TO ON</literal> statement. In autocommit mode, each
   command is automatically committed unless it is inside an explicit
   transaction block. This mode can be explicitly turned off using
   <literal>EXEC SQL SET AUTOCOMMIT TO OFF</literal>.
  </para>
 </sect1>

 <sect1 id="ecpg-set-connection">
  <title>Choosing a Connection</title>

  <para>
   The SQL statements shown in the previous section are executed on
   the current connection, that is, the most recently opened one.  If
   an application needs to manage multiple connections, then there are
   two ways to handle this.
  </para>

  <para>
   The first option is to explicitly choose a connection for each SQL
   statement, for example:
<programlisting>
EXEC SQL AT <replaceable>connection-name</replaceable> SELECT ...;
</programlisting>
   This option is particularly suitable if the application needs to
   use several connections in mixed order.
  </para>

  <para>
   If your application uses multiple threads of execution, they cannot share a
   connection concurrently. You must either explicitly control access to the connection
   (using mutexes) or use a connection for each thread. If each thread uses its own connection,
   you will need to use the AT clause to specify which connection the thread will use.
  </para>

  <para>
   The second option is to execute a statement to switch the current
   connection.  That statement is:
<programlisting>
EXEC SQL SET CONNECTION <replaceable>connection-name</replaceable>;
</programlisting>
   This option is particularly convenient if many statements are to be
   executed on the same connection.  It is not thread-aware.
  </para>
 </sect1>

 <sect1 id="ecpg-variables">
  <title>Using Host Variables</title>

  <para>
   In <xref linkend="ecpg-commands"> you saw how you can execute SQL
   statements from an embedded SQL program.  Some of those statements
   only used fixed values and did not provide a way to insert
   user-supplied values into statements or have the program process
   the values returned by the query.  Those kinds of statements are
   not really useful in real applications.  This section explains in
   detail how you can pass data between your C program and the
   embedded SQL statements using a simple mechanism called
   <firstterm>host variables</firstterm>. In an embedded SQL program  we
   consider the SQL statements to be <firstterm>guests</firstterm> in the C
   program code which is the <firstterm>host language</firstterm>. Therefore
   the variables of the C program are called <firstterm>host
   variables</firstterm>.
  </para>

  <sect2>
   <title>Overview</title>

   <para>
    Passing data between the C program and the SQL statements is
    particularly simple in embedded SQL.  Instead of having the
    program paste the data into the statement, which entails various
    complications, such as properly quoting the value, you can simply
    write the name of a C variable into the SQL statement, prefixed by
    a colon.  For example:
<programlisting>
EXEC SQL INSERT INTO sometable VALUES (:v1, 'foo', :v2);
</programlisting>
    This statements refers to two C variables named
    <varname>v1</varname> and <varname>v2</varname> and also uses a
    regular SQL string literal, to illustrate that you are not
    restricted to use one kind of data or the other.
   </para>

   <para>
    This style of inserting C variables in SQL statements works
    anywhere a value expression is expected in an SQL statement.
   </para>
  </sect2>

  <sect2>
   <title>Declare Sections</title>

   <para>
    To pass data from the program to the database, for example as
    parameters in a query, or to pass data from the database back to
    the program, the C variables that are intended to contain this
    data need to be declared in specially marked sections, so the
    embedded SQL preprocessor is made aware of them.
   </para>

   <para>
    This section starts with:
<programlisting>
EXEC SQL BEGIN DECLARE SECTION;
</programlisting>
    and ends with:
<programlisting>
EXEC SQL END DECLARE SECTION;
</programlisting>
    Between those lines, there must be normal C variable declarations,
    such as:
<programlisting>
int   x = 4;
char  foo[16], bar[16];
</programlisting>
    As you can see, you can optionally assign an initial value to the variable.
    The variable's scope is determined by the location of its declaring
    section within the program.
    You can also declare variables with the following syntax which implicitly
    creates a declare section:
<programlisting>
EXEC SQL int i = 4;
</programlisting>
    You can have as many declare sections in a program as you like.
   </para>

   <para>
    The declarations are also echoed to the output file as normal C
    variables, so there's no need to declare them again.  Variables
    that are not intended to be used in SQL commands can be declared
    normally outside these special sections.
   </para>

   <para>
    The definition of a structure or union also must be listed inside
    a <literal>DECLARE</> section. Otherwise the preprocessor cannot
    handle these types since it does not know the definition.
   </para>
  </sect2>

  <sect2>
   <title>Different types of host variables</title>
   <para>
    As a host variable you can also use arrays, typedefs, structs and
    pointers. Moreover there are special types of host variables that exist
    only in ECPG.
   </para>

   <para>
    A few examples on host variables:
    <variablelist>
     <varlistentry>
      <term>Arrays</term>
      <listitem>
      <para>
       One of the most common uses of an array declaration is probably the
       allocation of a char array as in:
<programlisting>
EXEC SQL BEGIN DECLARE SECTION;
    char str[50];
EXEC SQL END DECLARE SECTION;
</programlisting>
       Note that you have to take care of the length for yourself. If you use
       this host variable as the target variable of a query which returns a
       string with more than 49 characters, a buffer overflow occurs.
      </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term>Typedefs</term>
      <listitem>
      <para>
      Use the <literal>typedef</literal> keyword to map new types to already
      existing types.
<programlisting>
EXEC SQL BEGIN DECLARE SECTION;
    typedef char mychartype[40];
    typedef long serial_t;
EXEC SQL END DECLARE SECTION;
</programlisting>
       Note that you could also use:
<programlisting>
EXEC SQL TYPE serial_t IS long;
</programlisting>
       This declaration does not need to be part of a declare section.
      </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term>Pointers</term>
      <listitem>
      <para>
       You can declare pointers to the most common types. Note however that
       you cannot use pointers as target variables of queries without
       auto-allocation. See <xref linkend="ecpg-descriptors"> for more
       information on auto-allocation.
      </para>
<programlisting>
EXEC SQL BEGIN DECLARE SECTION;
    int   *intp;
    char **charp;
EXEC SQL END DECLARE SECTION;
</programlisting>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term>Special types of variables</term>
      <listitem>
       <para>
        ECPG contains some special types that help you to interact easily with
        data from the SQL server. For example it has implemented support for
        the <type>varchar</>, <type>numeric</>, <type>date</>, <type>timestamp</>, and <type>interval</> types.
        <xref linkend="ecpg-pgtypes"> contains basic functions to deal with
        those types, such that you do not need to send a query to the SQL
        server just for adding an interval to a timestamp for example.
       </para>
       <para>
        The special type <type>VARCHAR</type> 
        is converted into a named <type>struct</> for every variable. A
        declaration like:
<programlisting>
VARCHAR var[180];
</programlisting>
         is converted into:
<programlisting>
struct varchar_var { int len; char arr[180]; } var;
</programlisting>
        This structure is suitable for interfacing with SQL datums of type
        <type>varchar</type>.
       </para>
      </listitem>
     </varlistentry>
    </variablelist>
   </para>
  </sect2>

  <sect2>
   <title><command>SELECT INTO</command> and <command>FETCH INTO</command></title>

   <para>
    Now you should be able to pass data generated by your program into
    an SQL command.  But how do you retrieve the results of a query?
    For that purpose, embedded SQL provides special variants of the
    usual commands <command>SELECT</command> and
    <command>FETCH</command>.  These commands have a special
    <literal>INTO</literal> clause that specifies which host variables
    the retrieved values are to be stored in.
   </para>

   <para>
    Here is an example:
<programlisting>
/*
 * assume this table:
 * CREATE TABLE test1 (a int, b varchar(50));
 */

EXEC SQL BEGIN DECLARE SECTION;
int v1;
VARCHAR v2;
EXEC SQL END DECLARE SECTION;

 ...

EXEC SQL SELECT a, b INTO :v1, :v2 FROM test;
</programlisting>
    So the <literal>INTO</literal> clause appears between the select
    list and the <literal>FROM</literal> clause.  The number of
    elements in the select list and the list after
    <literal>INTO</literal> (also called the target list) must be
    equal.
   </para>

   <para>
    Here is an example using the command <command>FETCH</command>:
<programlisting>
EXEC SQL BEGIN DECLARE SECTION;
int v1;
VARCHAR v2;
EXEC SQL END DECLARE SECTION;

 ...

EXEC SQL DECLARE foo CURSOR FOR SELECT a, b FROM test;

 ...

do {
    ...
    EXEC SQL FETCH NEXT FROM foo INTO :v1, :v2;
    ...
} while (...);
</programlisting>
    Here the <literal>INTO</literal> clause appears after all the
    normal clauses.
   </para>

   <para>
    Both of these methods only allow retrieving one row at a time.  If
    you need to process result sets that potentially contain more than
    one row, you need to use a cursor, as shown in the second example.
   </para>
  </sect2>

  <sect2>
   <title>Indicators</title>

   <para>
    The examples above do not handle null values.  In fact, the
    retrieval examples will raise an error if they fetch a null value
    from the database.  To be able to pass null values to the database
    or retrieve null values from the database, you need to append a
    second host variable specification to each host variable that
    contains data.  This second host variable is called the
    <firstterm>indicator</firstterm> and contains a flag that tells
    whether the datum is null, in which case the value of the real
    host variable is ignored.  Here is an example that handles the
    retrieval of null values correctly:
<programlisting>
EXEC SQL BEGIN DECLARE SECTION;
VARCHAR val;
int val_ind;
EXEC SQL END DECLARE SECTION:

 ...

EXEC SQL SELECT b INTO :val :val_ind FROM test1;
</programlisting>
    The indicator variable <varname>val_ind</varname> will be zero if
    the value was not null, and it will be negative if the value was
    null.
   </para>

   <para>
    The indicator has another function: if the indicator value is
    positive, it means that the value is not null, but it was
    truncated when it was stored in the host variable.
   </para>
  </sect2>
 </sect1>

 <sect1 id="ecpg-dynamic">
  <title>Dynamic SQL</title>

  <para>
   In many cases, the particular SQL statements that an application
   has to execute are known at the time the application is written.
   In some cases, however, the SQL statements are composed at run time
   or provided by an external source.  In these cases you cannot embed
   the SQL statements directly into the C source code, but there is a
   facility that allows you to call arbitrary SQL statements that you
   provide in a string variable.
  </para>

  <para>
   The simplest way to execute an arbitrary SQL statement is to use
   the command <command>EXECUTE IMMEDIATE</command>.  For example:
<programlisting>
EXEC SQL BEGIN DECLARE SECTION;
const char *stmt = "CREATE TABLE test1 (...);";
EXEC SQL END DECLARE SECTION;

EXEC SQL EXECUTE IMMEDIATE :stmt;
</programlisting>
   You cannot execute statements that retrieve data (e.g.,
   <command>SELECT</command>) this way.
  </para>

  <para>
   A more powerful way to execute arbitrary SQL statements is to
   prepare them once and execute the prepared statement as often as
   you like.  It is also possible to prepare a generalized version of
   a statement and then execute specific versions of it by
   substituting parameters.  When preparing the statement, write
   question marks where you want to substitute parameters later.  For
   example:
<programlisting>
EXEC SQL BEGIN DECLARE SECTION;
const char *stmt = "INSERT INTO test1 VALUES(?, ?);";
EXEC SQL END DECLARE SECTION;

EXEC SQL PREPARE mystmt FROM :stmt;
 ...
EXEC SQL EXECUTE mystmt USING 42, 'foobar';
</programlisting>
   If the statement you are executing returns values, then add an
   <literal>INTO</literal> clause:
<programlisting><![CDATA[
EXEC SQL BEGIN DECLARE SECTION;
const char *stmt = "SELECT a, b, c FROM test1 WHERE a > ?";
int v1, v2;
VARCHAR v3;
EXEC SQL END DECLARE SECTION;

EXEC SQL PREPARE mystmt FROM :stmt;
 ...
EXEC SQL EXECUTE mystmt INTO v1, v2, v3 USING 37;
]]>
</programlisting>
   An <command>EXECUTE</command> command can have an
   <literal>INTO</literal> clause, a <literal>USING</literal> clause,
   both, or neither.
  </para>

  <para>
   When you don't need the prepared statement anymore, you should
   deallocate it:
<programlisting>
EXEC SQL DEALLOCATE PREPARE <replaceable>name</replaceable>;
</programlisting>
  </para>
 </sect1>


 <sect1 id="ecpg-pgtypes">
  <title>pgtypes library</title>

  <para>
   The pgtypes library maps <productname>PostgreSQL</productname> database
   types to C equivalents that can be used in C programs. It also offers
   functions to do basic calculations with those types within C, i.e., without
   the help of the <productname>PostgreSQL</productname> server. See the
   following example:
<programlisting><![CDATA[
EXEC SQL BEGIN DECLARE SECTION;
   date date1;
   timestamp ts1, tsout;
   interval iv1;
   char *out;
EXEC SQL END DECLARE SECTION;

PGTYPESdate_today(&date1);
EXEC SQL SELECT started, duration INTO :ts1, :iv1 FROM datetbl WHERE d=:date1;
PGTYPEStimestamp_add_interval(&ts1, &iv1, &tsout);
out = PGTYPEStimestamp_to_asc(&tsout);
printf("Started + duration: %s\n", out);
free(out);
]]>
</programlisting>
  </para>

  <sect2>
   <title>The numeric type</title>
   <para>
    The numeric type offers to do calculations with arbitrary precision. See
    <xref linkend="datatype-numeric"> for the equivalent type in the
    <productname>PostgreSQL</> server. Because of the arbitrary precision this
    variable needs to be able to expand and shrink dynamically. That's why you
    can only create variables on the heap by means of the
    <function>PGTYPESnumeric_new</> and <function>PGTYPESnumeric_free</>
    functions. The decimal type, which is similar but limited in the precision,
    can be created on the stack as well as on the heap.
   </para>
   <para>
   The following functions can be used to work with the numeric type:
   <variablelist>
    <varlistentry>
     <term><function>PGTYPESnumeric_new</function></term>
     <listitem>
      <para>
      Request a pointer to a newly allocated numeric variable.
<synopsis>
numeric *PGTYPESnumeric_new(void);
</synopsis>
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><function>PGTYPESnumeric_free</function></term>
     <listitem>
      <para>
      Free a numeric type, release all of its memory.
<synopsis>
void PGTYPESnumeric_free(numeric *var);
</synopsis>
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><function>PGTYPESnumeric_from_asc</function></term>
     <listitem>
      <para>
       Parse a numeric type from its string notation.
<synopsis>
numeric *PGTYPESnumeric_from_asc(char *str, char **endptr);
</synopsis>
       Valid formats are for example:
        <literal>-2</literal>,
        <literal>.794</literal>,
        <literal>+3.44</literal>,
        <literal>592.49E07</literal> or
        <literal>-32.84e-4</literal>.
       If the value could be parsed successfully, a valid pointer is returned,
       else the NULL pointer. At the moment ecpg always parses the complete
       string and so it currently does not support to store the address of the
       first invalid character in <literal>*endptr</literal>. You can safely
       set <literal>endptr</literal> to NULL.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><function>PGTYPESnumeric_to_asc</function></term>
     <listitem>
      <para>
       Returns a pointer to a string allocated by <function>malloc</function> that contains the string
       representation of the numeric type <literal>num</literal>.
<synopsis>
char *PGTYPESnumeric_to_asc(numeric *num, int dscale);
</synopsis>
       The numeric value will be printed with <literal>dscale</literal> decimal
       digits, with rounding applied if necessary.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><function>PGTYPESnumeric_add</function></term>
     <listitem>
      <para>
       Add two numeric variables into a third one.
<synopsis>
int PGTYPESnumeric_add(numeric *var1, numeric *var2, numeric *result);
</synopsis>
       The function adds the variables <literal>var1</literal> and
       <literal>var2</literal> into the result variable
       <literal>result</literal>.
       The function returns 0 on success and -1 in case of error.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><function>PGTYPESnumeric_sub</function></term>
     <listitem>
      <para>
       Subtract two numeric variables and return the result in a third one.
<synopsis>
int PGTYPESnumeric_sub(numeric *var1, numeric *var2, numeric *result);
</synopsis>
       The function subtracts the variable <literal>var2</literal> from
       the variable <literal>var1</literal>. The result of the operation is
       stored in the variable <literal>result</literal>.
       The function returns 0 on success and -1 in case of error.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><function>PGTYPESnumeric_mul</function></term>
     <listitem>
      <para>
       Multiply two numeric variables and return the result in a third one.
<synopsis>
int PGTYPESnumeric_mul(numeric *var1, numeric *var2, numeric *result);
</synopsis>
       The function multiplies the variables <literal>var1</literal> and
       <literal>var2</literal>. The result of the operation is stored in the
       variable <literal>result</literal>.
       The function returns 0 on success and -1 in case of error.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><function>PGTYPESnumeric_div</function></term>
     <listitem>
      <para>
       Divide two numeric variables and return the result in a third one.
<synopsis>
int PGTYPESnumeric_div(numeric *var1, numeric *var2, numeric *result);
</synopsis>
       The function divides the variables <literal>var1</literal> by
       <literal>var2</literal>. The result of the operation is stored in the
       variable <literal>result</literal>.
       The function returns 0 on success and -1 in case of error.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><function>PGTYPESnumeric_cmp</function></term>
     <listitem>
      <para>
       Compare two numeric variables.
<synopsis>
int PGTYPESnumeric_cmp(numeric *var1, numeric *var2)
</synopsis>
       This function compares two numeric variables. In case of error,
       <literal>INT_MAX</literal> is returned. On success, the function
       returns one of three possible results:
       <itemizedlist>
        <listitem>
         <para>
          1, if <literal>var1</> is bigger than <literal>var2</>
         </para>
        </listitem>
        <listitem>
         <para>
          -1, if <literal>var1</> is smaller than <literal>var2</>
         </para>
        </listitem>
        <listitem>
         <para>
          0, if <literal>var1</> and <literal>var2</> are equal
         </para>
        </listitem>
       </itemizedlist>
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><function>PGTYPESnumeric_from_int</function></term>
     <listitem>
      <para>
       Convert an int variable to a numeric variable.
<synopsis>
int PGTYPESnumeric_from_int(signed int int_val, numeric *var);
</synopsis>
       This function accepts a variable of type signed int and stores it
       in the numeric variable <literal>var</>. Upon success, 0 is returned and
       -1 in case of a failure.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><function>PGTYPESnumeric_from_long</function></term>
     <listitem>
      <para>
       Convert a long int variable to a numeric variable.
<synopsis>
int PGTYPESnumeric_from_long(signed long int long_val, numeric *var);
</synopsis>
       This function accepts a variable of type signed long int and stores it
       in the numeric variable <literal>var</>. Upon success, 0 is returned and
       -1 in case of a failure.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><function>PGTYPESnumeric_copy</function></term>
     <listitem>
      <para>
       Copy over one numeric variable into another one.
<synopsis>
int PGTYPESnumeric_copy(numeric *src, numeric *dst);
</synopsis>
       This function copies over the value of the variable that
       <literal>src</literal> points to into the variable that <literal>dst</>
       points to. It returns 0 on success and -1 if an error occurs.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><function>PGTYPESnumeric_from_double</function></term>
     <listitem>
      <para>
       Convert a variable of type double to a numeric.
<synopsis>
int  PGTYPESnumeric_from_double(double d, numeric *dst);
</synopsis>
       This function accepts a variable of type double and stores the result
       in the variable that <literal>dst</> points to. It returns 0 on success
       and -1 if an error occurs.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><function>PGTYPESnumeric_to_double</function></term>
     <listitem>
      <para>
       Convert a variable of type numeric to double.
<synopsis>
int PGTYPESnumeric_to_double(numeric *nv, double *dp)
</synopsis>
       The function converts the numeric value from the variable that
       <literal>nv</> points to into the double variable that <literal>dp</> points
       to. It returns 0 on success and -1 if an error occurs, including
       overflow. On overflow, the global variable <literal>errno</> will be set
       to <literal>PGTYPES_NUM_OVERFLOW</> additionally.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><function>PGTYPESnumeric_to_int</function></term>
     <listitem>
      <para>
       Convert a variable of type numeric to int.
<synopsis>
int PGTYPESnumeric_to_int(numeric *nv, int *ip);
</synopsis>
       The function converts the numeric value from the variable that
       <literal>nv</> points to into the integer variable that <literal>ip</>
       points to. It returns 0 on success and -1 if an error occurs, including
       overflow. On overflow, the global variable <literal>errno</> will be set
       to <literal>PGTYPES_NUM_OVERFLOW</> additionally.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><function>PGTYPESnumeric_to_long</function></term>
     <listitem>
      <para>
       Convert a variable of type numeric to long.
<synopsis>
int PGTYPESnumeric_to_long(numeric *nv, long *lp);
</synopsis>
       The function converts the numeric value from the variable that
       <literal>nv</> points to into the long integer variable that
       <literal>lp</> points to. It returns 0 on success and -1 if an error
       occurs, including overflow. On overflow, the global variable
       <literal>errno</> will be set to <literal>PGTYPES_NUM_OVERFLOW</>
       additionally.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><function>PGTYPESnumeric_to_decimal</function></term>
     <listitem>
      <para>
       Convert a variable of type numeric to decimal.
<synopsis>
int PGTYPESnumeric_to_decimal(numeric *src, decimal *dst);
</synopsis>
       The function converts the numeric value from the variable that
       <literal>src</> points to into the decimal variable that
       <literal>dst</> points to. It returns 0 on success and -1 if an error
       occurs, including overflow. On overflow, the global variable
       <literal>errno</> will be set to <literal>PGTYPES_NUM_OVERFLOW</>
       additionally.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><function>PGTYPESnumeric_from_decimal</function></term>
     <listitem>
      <para>
       Convert a variable of type decimal to numeric.
<synopsis>
int PGTYPESnumeric_from_decimal(decimal *src, numeric *dst);
</synopsis>
       The function converts the decimal value from the variable that
       <literal>src</> points to into the numeric variable that
       <literal>dst</> points to. It returns 0 on success and -1 if an error
       occurs. Since the decimal type is implemented as a limited version of
       the numeric type, overflow cannot occur with this conversion.
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
   </para>
  </sect2>

  <sect2>
   <title>The date type</title>
   <para>
    The date type in C enables your programs to deal with data of the SQL type
    date. See <xref linkend="datatype-datetime"> for the equivalent type in the
    <productname>PostgreSQL</> server.
   </para>
   <para>
    The following functions can be used to work with the date type:
    <variablelist>
     <varlistentry id="PGTYPESdatefromtimestamp">
      <term><function>PGTYPESdate_from_timestamp</function></term>
      <listitem>
       <para>
        Extract the date part from a timestamp.
<synopsis>
date PGTYPESdate_from_timestamp(timestamp dt);
</synopsis>
        The function receives a timestamp as its only argument and returns the
        extracted date part from this timestamp.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="PGTYPESdatefromasc">
      <term><function>PGTYPESdate_from_asc</function></term>
      <listitem>
       <para>
       Parse a date from its textual representation.
<synopsis>
date PGTYPESdate_from_asc(char *str, char **endptr);
</synopsis>
        The function receives a C char* string <literal>str</> and a pointer to
        a C char* string <literal>endptr</>. At the moment ecpg always parses
        the complete string and so it currently does not support to store the
        address of the first invalid character in <literal>*endptr</literal>.
        You can safely set <literal>endptr</literal> to NULL.
       </para>
       <para>
        Note that the function always assumes MDY-formatted dates and there is
        currently no variable to change that within ecpg.
       </para>
       <para>
        <xref linkend="ecpg-pgtypesdate-from-asc-table"> shows the allowed input formats.
       </para>
        <table id="ecpg-pgtypesdate-from-asc-table">
         <title>Valid input formats for <function>PGTYPESdate_from_asc</function></title>
         <tgroup cols="2">
          <thead>
           <row>
            <entry>Input</entry>
            <entry>Result</entry>
           </row>
          </thead>
          <tbody>
           <row>
            <entry><literal>January 8, 1999</literal></entry>
            <entry><literal>January 8, 1999</literal></entry>
           </row>
           <row>
            <entry><literal>1999-01-08</literal></entry>
            <entry><literal>January 8, 1999</literal></entry>
           </row>
           <row>
            <entry><literal>1/8/1999</literal></entry>
            <entry><literal>January 8, 1999</literal></entry>
           </row>
           <row>
            <entry><literal>1/18/1999</literal></entry>
            <entry><literal>January 18, 1999</literal></entry>
           </row>
           <row>
            <entry><literal>01/02/03</literal></entry>
            <entry><literal>February 1, 2003</literal></entry>
           </row>
           <row>
            <entry><literal>1999-Jan-08</literal></entry>
            <entry><literal>January 8, 1999</literal></entry>
           </row>
           <row>
            <entry><literal>Jan-08-1999</literal></entry>
            <entry><literal>January 8, 1999</literal></entry>
           </row>
           <row>
            <entry><literal>08-Jan-1999</literal></entry>
            <entry><literal>January 8, 1999</literal></entry>
           </row>
           <row>
            <entry><literal>99-Jan-08</literal></entry>
            <entry><literal>January 8, 1999</literal></entry>
           </row>
           <row>
            <entry><literal>08-Jan-99</literal></entry>
            <entry><literal>January 8, 1999</literal></entry>
           </row>
           <row>
            <entry><literal>08-Jan-06</literal></entry>
            <entry><literal>January 8, 2006</literal></entry>
           </row>
           <row>
            <entry><literal>Jan-08-99</literal></entry>
            <entry><literal>January 8, 1999</literal></entry>
           </row>
           <row>
            <entry><literal>19990108</literal></entry>
            <entry><literal>ISO 8601; January 8, 1999</literal></entry>
           </row>
           <row>
            <entry><literal>990108</literal></entry>
            <entry><literal>ISO 8601; January 8, 1999</literal></entry>
           </row>
           <row>
            <entry><literal>1999.008</literal></entry>
            <entry><literal>year and day of year</literal></entry>
           </row>
           <row>
            <entry><literal>J2451187</literal></entry>
            <entry><literal>Julian day</literal></entry>
           </row>
           <row>
            <entry><literal>January 8, 99 BC</literal></entry>
            <entry><literal>year 99 before the Common Era</literal></entry>
           </row>
          </tbody>
         </tgroup>
        </table>
      </listitem>
     </varlistentry>

     <varlistentry id="PGTYPESdatetoasc">
      <term><function>PGTYPESdate_to_asc</function></term>
      <listitem>
       <para>
        Return the textual representation of a date variable.
<synopsis>
char *PGTYPESdate_to_asc(date dDate);
</synopsis>
        The function receives the date <literal>dDate</> as its only parameter.
        It will output the date in the form <literal>1999-01-18</>, i.e., in the
        <literal>YYYY-MM-DD</> format.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="PGTYPESdatejulmdy">
      <term><function>PGTYPESdate_julmdy</function></term>
      <listitem>
       <para>
        Extract the values for the day, the month and the year from a variable
        of type date.
<synopsis>
void PGTYPESdate_julmdy(date d, int *mdy);
</synopsis>
       <!-- almost same description as for rjulmdy() -->
        The function receives the date <literal>d</> and a pointer to an array
        of 3 integer values <literal>mdy</>. The variable name indicates
        the sequential order: <literal>mdy[0]</> will be set to contain the
        number of the month, <literal>mdy[1]</> will be set to the value of the
        day and <literal>mdy[2]</> will contain the year.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="PGTYPESdatemdyjul">
      <term><function>PGTYPESdate_mdyjul</function></term>
      <listitem>
       <para>
        Create a date value from an array of 3 integers that specify the
        day, the month and the year of the date.
<synopsis>
void PGTYPESdate_mdyjul(int *mdy, date *jdate);
</synopsis>
        The function receives the array of the 3 integers (<literal>mdy</>) as
        its first argument and as its second argument a pointer to a variable
        of type date that should hold the result of the operation.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="PGTYPESdatedayofweek">
      <term><function>PGTYPESdate_dayofweek</function></term>
      <listitem>
       <para>
        Return a number representing the day of the week for a date value.
<synopsis>
int PGTYPESdate_dayofweek(date d);
</synopsis>
        The function receives the date variable <literal>d</> as its only
        argument and returns an integer that indicates the day of the week for
        this date.
        <itemizedlist>
         <listitem>
          <para>
           0 - Sunday
          </para>
         </listitem>
         <listitem>
          <para>
           1 - Monday
          </para>
         </listitem>
         <listitem>
          <para>
           2 - Tuesday
          </para>
         </listitem>
         <listitem>
          <para>
           3 - Wednesday
          </para>
         </listitem>
         <listitem>
          <para>
           4 - Thursday
          </para>
         </listitem>
         <listitem>
          <para>
           5 - Friday
          </para>
         </listitem>
         <listitem>
          <para>
           6 - Saturday
          </para>
         </listitem>
        </itemizedlist>
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="PGTYPESdatetoday">
      <term><function>PGTYPESdate_today</function></term>
      <listitem>
       <para>
        Get the current date.
<synopsis>
void PGTYPESdate_today(date *d);
</synopsis>
        The function receives a pointer to a date variable (<literal>d</>)
        that it sets to the current date.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="PGTYPESdatefmtasc">
      <term><function>PGTYPESdate_fmt_asc</function></term>
      <listitem>
       <para>
        Convert a variable of type date to its textual representation using a
        format mask.
<synopsis>
int PGTYPESdate_fmt_asc(date dDate, char *fmtstring, char *outbuf);
</synopsis>
        The function receives the date to convert (<literal>dDate</>), the
        format mask (<literal>fmtstring</>) and the string that will hold the
        textual representation of the date (<literal>outbuf</>).
       </para>
       <para>
        On success, 0 is returned and a negative value if an error occurred.
       </para>
       <para>
        The following literals are the field specifiers you can use:
        <itemizedlist>
         <listitem>
          <para>
           <literal>dd</literal> - The number of the day of the month.
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>mm</literal> - The number of the month of the year.
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>yy</literal> - The number of the year as a two digit number.
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>yyyy</literal> - The number of the year as a four digit number.
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>ddd</literal> - The name of the day (abbreviated).
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>mmm</literal> - The name of the month (abbreviated).
          </para>
         </listitem>
        </itemizedlist>
        All other characters are copied 1:1 to the output string.
       </para>
       <para>
        <xref linkend="ecpg-pgtypesdate-fmt-asc-example-table"> indicates a few possible formats. This will give
        you an idea of how to use this function. All output lines are based on
        the same date: November 23, 1959.
       </para>
        <table id="ecpg-pgtypesdate-fmt-asc-example-table">
         <title>Valid input formats for <function>PGTYPESdate_fmt_asc</function></title>
         <tgroup cols="2">
          <thead>
           <row>
            <entry>fmt</entry>
            <entry>result</entry>
           </row>
          </thead>
          <tbody>
           <row>
            <entry><literal>mmddyy</literal></entry>
            <entry><literal>112359</literal></entry>
           </row>
           <row>
            <entry><literal>ddmmyy</literal></entry>
            <entry><literal>231159</literal></entry>
           </row>
           <row>
            <entry><literal>yymmdd</literal></entry>
            <entry><literal>591123</literal></entry>
           </row>
           <row>
            <entry><literal>yy/mm/dd</literal></entry>
            <entry><literal>59/11/23</literal></entry>
           </row>
           <row>
            <entry><literal>yy mm dd</literal></entry>
            <entry><literal>59 11 23</literal></entry>
           </row>
           <row>
            <entry><literal>yy.mm.dd</literal></entry>
            <entry><literal>59.11.23</literal></entry>
           </row>
           <row>
            <entry><literal>.mm.yyyy.dd.</literal></entry>
            <entry><literal>.11.1959.23.</literal></entry>
           </row>
           <row>
            <entry><literal>mmm. dd, yyyy</literal></entry>
            <entry><literal>Nov. 23, 1959</literal></entry>
           </row>
           <row>
            <entry><literal>mmm dd yyyy</literal></entry>
            <entry><literal>Nov 23 1959</literal></entry>
           </row>
           <row>
            <entry><literal>yyyy dd mm</literal></entry>
            <entry><literal>1959 23 11</literal></entry>
           </row>
           <row>
            <entry><literal>ddd, mmm. dd, yyyy</literal></entry>
            <entry><literal>Mon, Nov. 23, 1959</literal></entry>
           </row>
           <row>
            <entry><literal>(ddd) mmm. dd, yyyy</literal></entry>
            <entry><literal>(Mon) Nov. 23, 1959</literal></entry>
           </row>
          </tbody>
         </tgroup>
        </table>
      </listitem>
     </varlistentry>

     <varlistentry id="PGTYPESdatedefmtasc">
      <term><function>PGTYPESdate_defmt_asc</function></term>
      <listitem>
       <para>
        Use a format mask to convert a C char* string to a value of type
        date.
<synopsis>
int PGTYPESdate_defmt_asc(date *d, char *fmt, char *str);
</synopsis>
        <!-- same description as rdefmtdate -->
        The function receives a pointer to the date value that should hold the
        result of the operation (<literal>d</>), the format mask to use for
        parsing the date (<literal>fmt</>) and the C char* string containing
        the textual representation of the date (<literal>str</>). The textual
        representation is expected to match the format mask. However you do not
        need to have a 1:1 mapping of the string to the format mask. The
        function only analyzes the sequential order and looks for the literals
        <literal>yy</literal> or <literal>yyyy</literal> that indicate the
        position of the year, <literal>mm</literal> to indicate the position of
        the month and <literal>dd</literal> to indicate the position of the
        day.
       </para>
       <para>
        <xref linkend="ecpg-rdefmtdate-example-table"> indicates a few possible formats. This will give
        you an idea of how to use this function.
       </para>
        <table id="ecpg-rdefmtdate-example-table">
         <title>Valid input formats for <function>rdefmtdate</function></title>
         <tgroup cols="3">
          <thead>
           <row>
            <entry>fmt</entry>
            <entry>str</entry>
            <entry>result</entry>
           </row>
          </thead>
          <tbody>
           <row>
            <entry><literal>ddmmyy</literal></entry>
            <entry><literal>21-2-54</literal></entry>
            <entry><literal>1954-02-21</literal></entry>
           </row>
           <row>
            <entry><literal>ddmmyy</literal></entry>
            <entry><literal>2-12-54</literal></entry>
            <entry><literal>1954-12-02</literal></entry>
           </row>
           <row>
            <entry><literal>ddmmyy</literal></entry>
            <entry><literal>20111954</literal></entry>
            <entry><literal>1954-11-20</literal></entry>
           </row>
           <row>
            <entry><literal>ddmmyy</literal></entry>
            <entry><literal>130464</literal></entry>
            <entry><literal>1964-04-13</literal></entry>
           </row>
           <row>
            <entry><literal>mmm.dd.yyyy</literal></entry>
            <entry><literal>MAR-12-1967</literal></entry>
            <entry><literal>1967-03-12</literal></entry>
           </row>
           <row>
            <entry><literal>yy/mm/dd</literal></entry>
            <entry><literal>1954, February 3rd</literal></entry>
            <entry><literal>1954-02-03</literal></entry>
           </row>
           <row>
            <entry><literal>mmm.dd.yyyy</literal></entry>
            <entry><literal>041269</literal></entry>
            <entry><literal>1969-04-12</literal></entry>
           </row>
           <row>
            <entry><literal>yy/mm/dd</literal></entry>
            <entry><literal>In the year 2525, in the month of July, mankind will be alive on the 28th day</literal></entry>
            <entry><literal>2525-07-28</literal></entry>
           </row>
           <row>
            <entry><literal>dd-mm-yy</literal></entry>
            <entry><literal>I said on the 28th of July in the year 2525</literal></entry>
            <entry><literal>2525-07-28</literal></entry>
           </row>
           <row>
            <entry><literal>mmm.dd.yyyy</literal></entry>
            <entry><literal>9/14/58</literal></entry>
            <entry><literal>1958-09-14</literal></entry>
           </row>
           <row>
            <entry><literal>yy/mm/dd</literal></entry>
            <entry><literal>47/03/29</literal></entry>
            <entry><literal>1947-03-29</literal></entry>
           </row>
           <row>
            <entry><literal>mmm.dd.yyyy</literal></entry>
            <entry><literal>oct 28 1975</literal></entry>
            <entry><literal>1975-10-28</literal></entry>
           </row>
           <row>
            <entry><literal>mmddyy</literal></entry>
            <entry><literal>Nov 14th, 1985</literal></entry>
            <entry><literal>1985-11-14</literal></entry>
           </row>
          </tbody>
         </tgroup>
        </table>
      </listitem>
     </varlistentry>
    </variablelist>
   </para>
  </sect2>
 
  <sect2>
   <title>The timestamp type</title>
   <para>
    The timestamp type in C enables your programs to deal with data of the SQL
    type timestamp. See <xref linkend="datatype-datetime"> for the equivalent
    type in the <productname>PostgreSQL</> server.
   </para>
   <para>
    The following functions can be used to work with the timestamp type:
    <variablelist>
     <varlistentry id="PGTYPEStimestampfromasc">
      <term><function>PGTYPEStimestamp_from_asc</function></term>
      <listitem>
       <para>
        Parse a timestamp from its textual representation into a timestamp
        variable.
<synopsis>
timestamp PGTYPEStimestamp_from_asc(char *str, char **endptr);
</synopsis>
        The function receives the string to parse (<literal>str</>) and a
        pointer to a C char* (<literal>endptr</>).
        At the moment ecpg always parses
        the complete string and so it currently does not support to store the
        address of the first invalid character in <literal>*endptr</literal>.
        You can safely set <literal>endptr</literal> to NULL.
       </para>
       <para>
        The function returns the parsed timestamp on success. On error,
        <literal>PGTYPESInvalidTimestamp</literal> is returned and errno is
        set to <literal>PGTYPES_TS_BAD_TIMESTAMP</>. See <xref linkend="PGTYPESInvalidTimestamp"> for important notes on this value.
        
       </para>
       <para>
        In general, the input string can contain any combination of an allowed
        date specification, a whitespace character and an allowed time
        specification. Note that timezones are not supported by ecpg. It can
        parse them but does not apply any calculation as the
        <productname>PostgreSQL</> server does for example. Timezone
        specifiers are silently discarded.
       </para>
       <para>
        <xref linkend="ecpg-pgtypestimestamp-from-asc-example-table"> contains a few examples for input strings.
       </para>
        <table id="ecpg-pgtypestimestamp-from-asc-example-table">
         <title>Valid input formats for <function>PGTYPEStimestamp_from_asc</function></title>
         <tgroup cols="2">
          <thead>
           <row>
            <entry>Input</entry>
            <entry>Result</entry>
           </row>
          </thead>
          <tbody>
           <row>
            <entry><literal>1999-01-08 04:05:06</literal></entry>
            <entry><literal>1999-01-08 04:05:06</literal></entry>
           </row>
           <row>
            <entry><literal>January 8 04:05:06 1999 PST</literal></entry>
            <entry><literal>1999-01-08 04:05:06</literal></entry>
           </row>
           <row>
            <entry><literal>1999-Jan-08 04:05:06.789-8</literal></entry>
            <entry><literal>1999-01-08 04:05:06.789 (time zone specifier ignored)</literal></entry>
           </row>
           <row>
            <entry><literal>J2451187 04:05-08:00</literal></entry>
            <entry><literal>1999-01-08 04:05:00 (time zone specifier ignored)</literal></entry>
           </row>
          </tbody>
         </tgroup>
        </table>
      </listitem>
     </varlistentry>

     <varlistentry id="PGTYPEStimestamptoasc">
      <term><function>PGTYPEStimestamp_to_asc</function></term>
      <listitem>
       <para>
        Converts a date to a C char* string.
<synopsis>
char *PGTYPEStimestamp_to_asc(timestamp tstamp);
</synopsis>
        The function receives the timestamp <literal>tstamp</> as
        its only argument and returns an allocated string that contains the
        textual representation of the timestamp.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="PGTYPEStimestampcurrent">
      <term><function>PGTYPEStimestamp_current</function></term>
      <listitem>
       <para>
        Retrieve the current timestamp.
<synopsis>
void PGTYPEStimestamp_current(timestamp *ts);
</synopsis>
        The function retrieves the current timestamp and saves it into the
        timestamp variable that <literal>ts</> points to.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="PGTYPEStimestampfmtasc">
      <term><function>PGTYPEStimestamp_fmt_asc</function></term>
      <listitem>
       <para>
        Convert a timestamp variable to a C char* using a format mask.
<synopsis>
int PGTYPEStimestamp_fmt_asc(timestamp *ts, char *output, int str_len, char *fmtstr);
</synopsis>
        The function receives a pointer to the timestamp to convert as its
        first argument (<literal>ts</>), a pointer to the output buffer
        (<literal>output</>), the maximal length that has been allocated for
        the output buffer (<literal>str_len</literal>) and the format mask to
        use for the conversion (<literal>fmtstr</literal>).
       </para>
       <para>
        Upon success, the function returns 0 and a negative value if an
        error occurred.
       </para>
       <para>
        You can use the following format specifiers for the format mask. The
        format specifiers are the same ones that are used in the
        <function>strftime</> function in <productname>libc</productname>. Any
        non-format specifier will be copied into the output buffer. 
        <!-- This is from the FreeBSD man page:
             http://www.freebsd.org/cgi/man.cgi?query=strftime&apropos=0&sektion=3&manpath=FreeBSD+7.0-current&format=html
        -->
        <itemizedlist>
         <listitem>
          <para>
           <literal>%A</literal> - is replaced by national representation of
           the full weekday name.
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>%a</literal> - is replaced by national representation of
           the abbreviated weekday name.
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>%B</literal> - is replaced by national representation of
           the full month name.
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>%b</literal> - is replaced by national representation of
           the abbreviated month name.
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>%C</literal> - is replaced by (year / 100) as decimal
           number; single digits are preceded by a zero.
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>%c</literal> - is replaced by national representation of
           time and date.
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>%D</literal> - is equivalent to
           <literal>%m/%d/%y</literal>.
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>%d</literal> - is replaced by the day of the month as a
           decimal number (01-31).
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>%E*</literal> <literal>%O*</literal> -  POSIX locale
           extensions. The sequences
           <literal>%Ec</literal>
           <literal>%EC</literal> 
           <literal>%Ex</literal> 
           <literal>%EX</literal> 
           <literal>%Ey</literal> 
           <literal>%EY</literal> 
           <literal>%Od</literal> 
           <literal>%Oe</literal>
           <literal>%OH</literal> 
           <literal>%OI</literal> 
           <literal>%Om</literal> 
           <literal>%OM</literal> 
           <literal>%OS</literal> 
           <literal>%Ou</literal> 
           <literal>%OU</literal> 
           <literal>%OV</literal> 
           <literal>%Ow</literal> 
           <literal>%OW</literal> 
           <literal>%Oy</literal> 
           are supposed to provide alternative representations.
          </para>
          <para>
           Additionally <literal>%OB</literal> implemented to represent
           alternative months names (used standalone, without day mentioned).
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>%e</literal> - is replaced by the day of month as a decimal
           number (1-31); single digits are preceded by a blank.
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>%F</literal> - is equivalent to <literal>%Y-%m-%d</literal>.
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>%G</literal> - is replaced by a year as a decimal number
           with century. This year is the one that contains the greater part of
           the week (Monday as the first day of the week).
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>%g</literal> - is replaced by the same year as in
           <literal>%G</literal>, but as a decimal number without century
           (00-99).
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>%H</literal> - is replaced by the hour (24-hour clock) as a
           decimal number (00-23).
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>%h</literal> - the same as <literal>%b</literal>.
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>%I</literal> - is replaced by the hour (12-hour clock) as a
           decimal number (01-12).
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>%j</literal> - is replaced by the day of the year as a
           decimal number (001-366).
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>%k</literal> - is replaced by the hour (24-hour clock) as a
           decimal number (0-23); single digits are preceded by a blank.
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>%l</literal> - is replaced by the hour (12-hour clock) as a
           decimal number (1-12); single digits are preceded by a blank.
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>%M</literal> - is replaced by the minute as a decimal
           number (00-59).
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>%m</literal> - is replaced by the month as a decimal number
           (01-12).
          </para>
         </listitem>
         <listitem>
          <para>
          <literal>%n</literal> - is replaced by a newline.
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>%O*</literal> - the same as <literal>%E*</literal>.
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>%p</literal> - is replaced by national representation of
           either "ante meridiem" or "post meridiem" as appropriate.
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>%R</literal> - is equivalent to <literal>%H:%M</literal>.
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>%r</literal> - is equivalent to <literal>%I:%M:%S
           %p</literal>.
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>%S</literal> - is replaced by the second as a decimal
           number (00-60).
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>%s</literal> - is replaced by the number of seconds since
           the Epoch, UTC.
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>%T</literal> - is equivalent to <literal>%H:%M:%S</literal>
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>%t</literal> - is replaced by a tab.
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>%U</literal> - is replaced by the week number of the year
           (Sunday as the first day of the week) as a decimal number (00-53).
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>%u</literal> - is replaced by the weekday (Monday as the
           first day of the week) as a decimal number (1-7).
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>%V</literal> - is replaced by the week number of the year
           (Monday as the first day of the week) as a decimal number (01-53).
           If the week containing January 1 has four or more days in the new
           year, then it is week 1; otherwise it is the last week of the
           previous year, and the next week is week 1.
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>%v</literal> - is equivalent to
           <literal>%e-%b-%Y</literal>.
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>%W</literal> - is replaced by the week number of the year
           (Monday as the first day of the week) as a decimal number (00-53).
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>%w</literal> - is replaced by the weekday (Sunday as the
           first day of the week) as a decimal number (0-6).
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>%X</literal> - is replaced by national representation of
           the time.
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>%x</literal> - is replaced by national representation of
           the date.
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>%Y</literal> - is replaced by the year with century as a
           decimal number.
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>%y</literal> - is replaced by the year without century as a
           decimal number (00-99).
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>%Z</literal> - is replaced by the time zone name.
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>%z</literal> - is replaced by the time zone offset from
           UTC; a leading plus sign stands for east of UTC, a minus sign for
           west of UTC, hours and minutes follow with two digits each and no
           delimiter between them (common form for RFC 822 date headers).
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>%+</literal> - is replaced by national representation of
           the date and time.
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>%-*</literal> - GNU libc extension. Do not do any padding
           when performing numerical outputs.
          </para>
         </listitem>
         <listitem>
          <para>
           $_* - GNU libc extension.    Explicitly specify space for padding.
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>%0*</literal> - GNU libc extension. Explicitly specify zero
           for padding.
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>%%</literal> - is replaced by <literal>%</literal>.
          </para>
         </listitem>
        </itemizedlist>
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="PGTYPEStimestampsub">
      <term><function>PGTYPEStimestamp_sub</function></term>
      <listitem>
       <para>
        Subtract one timestamp from another one and save the result in a
        variable of type interval.
<synopsis>
int PGTYPEStimestamp_sub(timestamp *ts1, timestamp *ts2, interval *iv);
</synopsis>
        The function will subtract the timestamp variable that <literal>ts2</>
        points to from the timestamp variable that <literal>ts1</> points to
        and will store the result in the interval variable that <literal>iv</>
        points to.
       </para>
       <para>
        Upon success, the function returns 0 and a negative value if an
        error occurred.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="PGTYPEStimestampdefmtasc">
      <term><function>PGTYPEStimestamp_defmt_asc</function></term>
      <listitem>
       <para>
        Parse a timestamp value from its textual representation using a
        formatting mask.
<synopsis>
int PGTYPEStimestamp_defmt_asc(char *str, char *fmt, timestamp *d);
</synopsis>
        The function receives the textual representation of a timestamp in the
        variable <literal>str</> as well as the formatting mask to use in the
        variable <literal>fmt</>. The result will be stored in the variable
        that <literal>d</> points to.
       </para>
       <para>
        If the formatting mask <literal>fmt</> is NULL, the function will fall
        back to the default formatting mask which is <literal>%Y-%m-%d
        %H:%M:%S</literal>.
       </para>
       <para>
        This is the reverse function to <xref
        linkend="PGTYPEStimestampfmtasc">.  See the documentation there in
        order to find out about the possible formatting mask entries.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="PGTYPEStimestampaddinterval">
      <term><function>PGTYPEStimestamp_add_interval</function></term>
      <listitem>
       <para>
        Add an interval variable to a timestamp variable.
<synopsis>
int PGTYPEStimestamp_add_interval(timestamp *tin, interval *span, timestamp *tout);
</synopsis>
        The function receives a pointer to a timestamp variable <literal>tin</>
        and a pointer to an interval variable <literal>span</>. It adds the
        interval to the timestamp and saves the resulting timestamp in the
        variable that <literal>tout</> points to.
       </para>
       <para>
        Upon success, the function returns 0 and a negative value if an
        error occurred.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="PGTYPEStimestampsubinterval">
      <term><function>PGTYPEStimestamp_sub_interval</function></term>
      <listitem>
       <para>
        Subtract an interval variable from a timestamp variable.
<synopsis>
int PGTYPEStimestamp_sub_interval(timestamp *tin, interval *span, timestamp *tout);
</synopsis>
        The function subtracts the interval variable that <literal>span</>
        points to from the timestamp variable that <literal>tin</> points to
        and saves the result into the variable that <literal>tout</> points
        to.
       </para>
       <para>
        Upon success, the function returns 0 and a negative value if an
        error occurred.
       </para>
      </listitem>
     </varlistentry>
    </variablelist>
   </para>
  </sect2>

  <sect2>
   <title>The interval type</title>
   <para>
    The interval type in C enables your programs to deal with data of the SQL
    type interval. See <xref linkend="datatype-datetime"> for the equivalent
    type in the <productname>PostgreSQL</> server.
   </para>
   <para>
    The following functions can be used to work with the interval type:
    <variablelist>

     <varlistentry id="PGTYPESintervalnew">
      <term><function>PGTYPESinterval_new</function></term>
      <listitem>
       <para>
        Return a pointer to a newly allocated interval variable.
<synopsis>
interval *PGTYPESinterval_new(void);
</synopsis>
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="PGTYPESintervalfree">
      <term><function>PGTYPESinterval_free</function></term>
      <listitem>
       <para>
        Release the memory of a previously allocated interval variable.
<synopsis>
void PGTYPESinterval_new(interval *intvl);
</synopsis>
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="PGTYPESintervalfromasc">
      <term><function>PGTYPESinterval_from_asc</function></term>
      <listitem>
       <para>
        Parse an interval from its textual representation.
<synopsis>
interval *PGTYPESinterval_from_asc(char *str, char **endptr);
</synopsis>
        The function parses the input string <literal>str</> and returns a
        pointer to an allocated interval variable.
        At the moment ecpg always parses
        the complete string and so it currently does not support to store the
        address of the first invalid character in <literal>*endptr</literal>.
        You can safely set <literal>endptr</literal> to NULL.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="PGTYPESintervaltoasc">
      <term><function>PGTYPESinterval_to_asc</function></term>
      <listitem>
       <para>
        Convert a variable of type interval to its textual representation.
<synopsis>
char *PGTYPESinterval_to_asc(interval *span);
</synopsis>
        The function converts the interval variable that <literal>span</>
        points to into a C char*. The output looks like this example:
        <literal>@ 1 day 12 hours 59 mins 10 secs</literal>.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="PGTYPESintervalcopy">
      <term><function>PGTYPESinterval_copy</function></term>
      <listitem>
       <para>
        Copy a variable of type interval.
<synopsis>
int PGTYPESinterval_copy(interval *intvlsrc, interval *intvldest);
</synopsis>
        The function copies the interval variable that <literal>intvlsrc</>
        points to into the variable that <literal>intvldest</> points to. Note
        that you need to allocate the memory for the destination variable
        before.
       </para>
      </listitem>
     </varlistentry>
    </variablelist>
   </para>
  </sect2>

  <sect2>
   <title>The decimal type</title>
   <para>
     The decimal type is similar to the numeric type. However it is limited to
     a maximal precision of 30 significant digits. In contrast to the numeric
     type which can be created on the heap only, the decimal type can be
     created either on the stack or on the heap (by means of the functions
     PGTYPESdecimal_new() and PGTYPESdecimal_free(). There are a lot of other
     functions that deal with the decimal type in the <productname>Informix</productname> compatibility
     mode described in <xref linkend="ecpg-informix-compat">.
   </para>
   <para>
    The following functions can be used to work with the decimal type and are
    not only contained in the <literal>libcompat</> library.
    <variablelist>
     <varlistentry>
      <term><function>PGTYPESdecimal_new</function></term>
      <listitem>
       <para>
       Request a pointer to a newly allocated decimal variable.
<synopsis>
decimal *PGTYPESdecimal_new(void);
</synopsis>
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><function>PGTYPESdecimal_free</function></term>
      <listitem>
       <para>
       Free a decimal type, release all of its memory.
<synopsis>
void PGTYPESdecimal_free(decimal *var);
</synopsis>
       </para>
      </listitem>
     </varlistentry>
    </variablelist>
   </para>
  </sect2>
 
   <sect2>
    <title>errno values of pgtypeslib </title>
   <para>
    <variablelist>
     <varlistentry>
      <term><literal>PGTYPES_NUM_BAD_NUMERIC</literal></term>
      <listitem>
       <para>
        An argument should contain a numeric variable (or point to a numeric
        variable) but in fact its in-memory representation was invalid.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>PGTYPES_NUM_OVERFLOW</literal></term>
      <listitem>
       <para>
        An overflow occurred. Since the numeric type can deal with almost
        arbitrary precision, converting a numeric variable into other types
        might cause overflow.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>PGTYPES_NUM_UNDERFLOW</literal></term>
      <listitem>
       <para>
        An underflow occurred. Since the numeric type can deal with almost
        arbitrary precision, converting a numeric variable into other types
        might cause underflow.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>PGTYPES_NUM_DIVIDE_ZERO</literal></term>
      <listitem>
       <para>
        A division by zero has been attempted.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>PGTYPES_DATE_BAD_DATE</literal></term>
      <listitem>
       <para>
        
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>PGTYPES_DATE_ERR_EARGS</literal></term>
      <listitem>
       <para>
        
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>PGTYPES_DATE_ERR_ENOSHORTDATE</literal></term>
      <listitem>
       <para>
        
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>PGTYPES_INTVL_BAD_INTERVAL</literal></term>
      <listitem>
       <para>
        
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>PGTYPES_DATE_ERR_ENOTDMY</literal></term>
      <listitem>
       <para>
        
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>PGTYPES_DATE_BAD_DAY</literal></term>
      <listitem>
       <para>
        
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>PGTYPES_DATE_BAD_MONTH</literal></term>
      <listitem>
       <para>
        
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>PGTYPES_TS_BAD_TIMESTAMP</literal></term>
      <listitem>
       <para>
        
       </para>
      </listitem>
     </varlistentry>
    </variablelist>
   </para>
  </sect2>

   <sect2>
    <title>Special constants of pgtypeslib </title>
   <para>
    <variablelist>
     <varlistentry id="PGTYPESInvalidTimestamp">
      <term><literal>PGTYPESInvalidTimestamp</literal></term>
      <listitem>
       <para>
        A value of type timestamp representing an invalid time stamp. This is
        returned by the function <function>PGTYPEStimestamp_from_asc</> on
        parse error.
        Note that due to the internal representation of the timestamp datatype,
        <literal>PGTYPESInvalidTimestamp</literal> is also a valid timestamp at
        the same time. It is set to <literal>1899-12-31 23:59:59</>. In order
        to detect errors, make sure that your application does not only test
        for <literal>PGTYPESInvalidTimestamp</literal> but also for
        <literal>errno != 0</> after each call to
        <function>PGTYPEStimestamp_from_asc</>.
       </para>
      </listitem>
     </varlistentry>
    </variablelist>
   </para>
  </sect2>
 </sect1>

 <sect1 id="ecpg-descriptors">
  <title>Using Descriptor Areas</title>

  <para>
   An SQL descriptor area is a more sophisticated method for processing
   the result of a <command>SELECT</command>, <command>FETCH</command> or
   a <command>DESCRIBE</command> statement. An SQL descriptor area groups
   the data of one row of data together with metadata items into one
   data structure.  The metadata is particularly useful when executing
   dynamic SQL statements, where the nature of the result columns might
   not be known ahead of time. PostgreSQL provides two ways to use
   Descriptor Areas: the named SQL Descriptor Areas and the C-structure
   SQLDAs.
  </para>

  <sect2 id="ecpg-named-descriptors">
   <title>Named SQL Descriptor Areas</title>

   <para>
    A named SQL descriptor area consists of a header, which contains
    information concerning the entire descriptor, and one or more item
    descriptor areas, which basically each describe one column in the
    result row.
   </para>

   <para>
    Before you can use an SQL descriptor area, you need to allocate one:
<programlisting>
EXEC SQL ALLOCATE DESCRIPTOR <replaceable>identifier</replaceable>;
</programlisting>
    The identifier serves as the <quote>variable name</quote> of the
    descriptor area.  <remark>The scope of the allocated descriptor is WHAT?.</remark>
    When you don't need the descriptor anymore, you should deallocate
    it:
<programlisting>
EXEC SQL DEALLOCATE DESCRIPTOR <replaceable>identifier</replaceable>;
</programlisting>
   </para>

   <para>
    To use a descriptor area, specify it as the storage target in an
    <literal>INTO</literal> clause, instead of listing host variables:
<programlisting>
EXEC SQL FETCH NEXT FROM mycursor INTO SQL DESCRIPTOR mydesc;
</programlisting>
    If the resultset is empty, the Descriptor Area will still contain
    the metadata from the query, i.e. the field names.
   </para>

   <para>
    For not yet executed prepared queries, the <command>DESCRIBE</command>
    statement can be used to get the metadata of the resultset:
<programlisting> 
EXEC SQL BEGIN DECLARE SECTION;
char *sql_stmt = "SELECT * FROM table1";
EXEC SQL END DECLARE SECTION;

EXEC SQL PREPARE stmt1 FROM :sql_stmt;
EXEC SQL DESCRIBE stmt1 INTO SQL DESCRIPTOR mydesc;
</programlisting>
   </para>

   <para>
    Before PostgreSQL 9.0, the <literal>SQL</literal> keyword was optional,
    so using <literal>DESCRIPTOR</literal> and <literal>SQL DESCRIPTOR</literal>
    produced named SQL Descriptor Areas. Now it is mandatory, omitting
    the <literal>SQL</literal> keyword produces SQLDA Descriptor Areas,
    see <xref linkend="ecpg-sqlda-descriptors">. 
   </para>

   <para>
    In <command>DESCRIBE</command> and <command>FETCH</command> statements,
    the <literal>INTO</literal> and <literal>USING</literal> keywords can be
    used to similarly: they produce the resultset and the metadata in a
    Descriptor Area.
   </para>

   <para>
    Now how do you get the data out of the descriptor area?  You can
    think of the descriptor area as a structure with named fields.  To
    retrieve the value of a field from the header and store it into a
    host variable, use the following command:
<programlisting>
EXEC SQL GET DESCRIPTOR <replaceable>name</replaceable> :<replaceable>hostvar</replaceable> = <replaceable>field</replaceable>;
</programlisting>
    Currently, there is only one header field defined:
    <replaceable>COUNT</replaceable>, which tells how many item
    descriptor areas exist (that is, how many columns are contained in
    the result).  The host variable needs to be of an integer type.  To
    get a field from the item descriptor area, use the following
    command:
<programlisting>
EXEC SQL GET DESCRIPTOR <replaceable>name</replaceable> VALUE <replaceable>num</replaceable> :<replaceable>hostvar</replaceable> = <replaceable>field</replaceable>;
</programlisting>
    <replaceable>num</replaceable> can be a literal integer or a host
    variable containing an integer. Possible fields are:

    <variablelist>
     <varlistentry>
      <term><literal>CARDINALITY</literal> (integer)</term>
      <listitem>
       <para>
        number of rows in the result set
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>DATA</literal></term>
      <listitem>
       <para>
        actual data item (therefore, the data type of this field
        depends on the query)
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>DATETIME_INTERVAL_CODE</literal> (integer)</term>
      <listitem>
       <para>
        ?
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>DATETIME_INTERVAL_PRECISION</literal> (integer)</term>
      <listitem>
       <para>
        not implemented
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>INDICATOR</literal> (integer)</term>
      <listitem>
       <para>
        the indicator (indicating a null value or a value truncation)
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>KEY_MEMBER</literal> (integer)</term>
      <listitem>
       <para>
        not implemented
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>LENGTH</literal> (integer)</term>
      <listitem>
       <para>
        length of the datum in characters
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>NAME</literal> (string)</term>
      <listitem>
       <para>
        name of the column
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>NULLABLE</literal> (integer)</term>
      <listitem>
       <para>
        not implemented
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>OCTET_LENGTH</literal> (integer)</term>
      <listitem>
       <para>
        length of the character representation of the datum in bytes
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>PRECISION</literal> (integer)</term>
      <listitem>
       <para>
        precision (for type <type>numeric</type>)
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>RETURNED_LENGTH</literal> (integer)</term>
      <listitem>
       <para>
        length of the datum in characters
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>RETURNED_OCTET_LENGTH</literal> (integer)</term>
      <listitem>
       <para>
        length of the character representation of the datum in bytes
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>SCALE</literal> (integer)</term>
      <listitem>
       <para>
        scale (for type <type>numeric</type>)
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>TYPE</literal> (integer)</term>
      <listitem>
       <para>
        numeric code of the data type of the column
       </para>
      </listitem>
     </varlistentry>
    </variablelist>
   </para>

   <para>
    In <command>EXECUTE</command>, <command>DECLARE</command> and <command>OPEN</command>
    statements, the effect of the <literal>INTO</literal> and <literal>USING</literal>
    keywords are different. A Descriptor Area can also be manually built to
    provide the input parameters for a query or a cursor and
    <literal>USING SQL DESCRIPTOR <replaceable>name</replaceable></literal>
    is the way to pass the input parameters into a parametrized query. The statement
    to build a named SQL Descriptor Area is below:
<programlisting>
EXEC SQL SET DESCRIPTOR <replaceable>name</replaceable> VALUE <replaceable>num</replaceable> <replaceable>field</replaceable> = :<replaceable>hostvar</replaceable>;
</programlisting>
   </para>

   <para>
    PostgreSQL supports retrieving more that one record in one <command>FETCH</command>
    statement and storing the data in host variables in this case assumes that the
    variable is an array. E.g.:
<programlisting>
EXEC SQL BEGIN DECLARE SECTION;
int id[5];
EXEC SQL END DECLARE SECTION;

EXEC SQL FETCH 5 FROM mycursor INTO SQL DESCRIPTOR mydesc;

EXEC SQL GET DESCRIPTOR mydesc VALUE 1 :id = DATA;
</programlisting>

   </para>

  </sect2>

  <sect2 id="ecpg-sqlda-descriptors">
   <title>SQLDA Descriptor Areas</title>

   <para>
    An SQLDA Descriptor Area is a C language structure which can be also used
    to get the resultset and the metadata of a query. One structure stores one
    record from the resultset.
<programlisting>
EXEC SQL include sqlda.h;
sqlda_t         *mysqlda;

EXEC SQL FETCH 3 FROM mycursor INTO DESCRIPTOR mysqlda;
</programlisting>
    Note that the <literal>SQL</literal> keyword is omitted. The paragraphs about
    the use cases of the <literal>INTO</literal> and <literal>USING</literal>
    keywords in <xref linkend="ecpg-named-descriptors"> also apply here with an addition.
    In a <command>DESCRIBE</command> statement the <literal>DESCRIPTOR</literal>
    keyword can be completely omitted if the <literal>INTO</literal> keyword is used:
<programlisting>
EXEC SQL DESCRIBE prepared_statement INTO mysqlda;
</programlisting>
   </para>

   <para>
    The structure of SQLDA is:
<programlisting>
#define NAMEDATALEN 64

struct sqlname
{
        short           length;
        char            data[NAMEDATALEN];
};

struct sqlvar_struct
{
        short           sqltype;
        short           sqllen;
        char       *sqldata;
        short      *sqlind;
        struct sqlname sqlname;
};

struct sqlda_struct
{
        char            sqldaid[8];
        long            sqldabc;
        short           sqln;
        short           sqld;
        struct sqlda_struct *desc_next;
        struct sqlvar_struct    sqlvar[1];
};

typedef struct sqlvar_struct    sqlvar_t;
typedef struct sqlda_struct     sqlda_t;
</programlisting>
   </para>

   <para>
    The allocated data for an SQLDA structure is variable as it depends on the
    number of fields in a resultset and also depends on the length of the string
    data values in a record. The individual fields of the <literal>SQLDA</literal>
    structure are:

    <variablelist>
     <varlistentry>
      <term><literal>sqldaid</></term>
      <listitem>
       <para>
        It contains the "<literal>SQLDA  </literal>" literal string.
       </para>
      </listitem>
     </varlistentry>
     <varlistentry>
      <term><literal>sqldabc</></term>
      <listitem>
       <para>
        It contains the size of the allocated space in bytes.
       </para>
      </listitem>
     </varlistentry>
     <varlistentry>
      <term><literal>sqln</></term>
      <listitem>
       <para>
        It contains the number of input parameters for a parametrized query
        case it's passed into <command>OPEN</command>, <command>DECLARE</command> or
        <command>EXECUTE</command> statements using the <literal>USING</literal>
        keyword. In case it's used as output of <command>SELECT</command>,
        <command>EXECUTE</command> or <command>FETCH</command> statements,
        its value is the same as <literal>sqld</literal>
        statement
       </para>
      </listitem>
     </varlistentry>
     <varlistentry>
      <term><literal>sqld</></term>
      <listitem>
       <para>
        It contains the number of fields in a resultset.
       </para>
      </listitem>
     </varlistentry>
     <varlistentry>
      <term><literal>desc_next</></term>
      <listitem>
       <para>
        If the query returns more than one records, multiple linked SQLDA structures
        are returned, the first record is stored in the SQLDA returned in the
       </para>
      </listitem>
     </varlistentry>
     <varlistentry>
      <term><literal>sqlvar</></term>
      <listitem>
       <para>
        This is the array of the fields in the resultset. The fields are:

        <variablelist>

         <varlistentry>
         <term><literal>sqltype</></term>
          <listitem>
           <para>
            It contains the type identifier of the field. For values,
            see <literal>enum ECPGttype</literal> in <literal>ecpgtype.h</literal>.
           </para>
          </listitem>
         </varlistentry>

         <varlistentry>
         <term><literal>sqllen</></term>
          <listitem>
           <para>
            It contains the binary length of the field. E.g. 4 bytes for ECPGt_int.
           </para>
          </listitem>
         </varlistentry>

         <varlistentry>
         <term><literal>sqldata</></term>
          <listitem>
           <para>
            <literal>(char *)sqldata</literal> points to the data.
           </para>
          </listitem>
         </varlistentry>

         <varlistentry>
         <term><literal>sqlind</></term>
          <listitem>
           <para>
            <literal>(char *)sqlind</literal> points to the NULL indicator for data.
            0 means NOT NULL, -1 means NULL.
           </para>
          </listitem>
         </varlistentry>

         <varlistentry>
         <term><literal>sqlname</></term>
          <listitem>
           <para>
            <literal>struct sqlname sqlname</literal> contains the name of the field
            in a structure:
<programlisting>
struct sqlname
{
        short           length;
        char            data[NAMEDATALEN];
};
</programlisting>

            <variablelist>
             <varlistentry>
              <term><literal>length</></term>
               <listitem>
                <para>
                 <literal>sqlname.length</literal> contains the length of the field name.
                </para>
               </listitem>
              </varlistentry>
             <varlistentry>
              <term><literal>data</></term>
               <listitem>
                <para>
                 <literal>sqlname.data</literal> contains the actual field name.
                </para>
               </listitem>
              </varlistentry>
            </variablelist>
           </para>
          </listitem>
         </varlistentry>

        </variablelist>
       </para>
      </listitem>
     </varlistentry>
    </variablelist>
   </para>

  </sect2>

 </sect1>

 <sect1 id="ecpg-informix-compat">
  <title><productname>Informix</productname> compatibility mode</title>
  <para>
   ecpg can be run in a so-called <firstterm>Informix compatibility mode</>. If
   this mode is active, it tries to behave as if it were the <productname>Informix</productname>
   precompiler for <productname>Informix</productname> E/SQL. Generally spoken this will allow you to use
   the dollar sign instead of the <literal>EXEC SQL</> primitive to introduce
   embedded SQL commands.:
<programlisting>
   $int j = 3;
   $CONNECT TO :dbname;
   $CREATE TABLE test(i INT PRIMARY KEY, j INT);
   $INSERT INTO test(i, j) VALUES (7, :j);
   $COMMIT;
</programlisting>
  </para>
  <para>
   There are two compatibility modes: INFORMIX, INFORMIX_SE
  </para>
  <para>
   When linking programs that use this compatibility mode, remember to link
   against <literal>libcompat</> that is shipped with ecpg.
  </para>
  <para>
   Besides the previously explained syntactic sugar, the <productname>Informix</productname> compatibility
   mode ports some functions for input, output and transformation of data as
   well as embedded SQL statements known from E/SQL to ecpg.
  </para>
  <para>
   <productname>Informix</productname> compatibility mode is closely connected to the pgtypeslib library
   of ecpg. pgtypeslib maps SQL data types to data types within the C host
   program and most of the additional functions of the <productname>Informix</productname> compatibility
   mode allow you to operate on those C host program types. Note however that
   the extent of the compatibility is limited. It does not try to copy <productname>Informix</productname>
   behavior; it allows you to do more or less the same operations and gives
   you functions that have the same name and the same basic behavior but it is
   no drop-in replacement if you are using <productname>Informix</productname> at the moment. Moreover,
   some of the data types are different. For example,
   <productname>PostgreSQL's</productname> datetime and interval types do not
   know about ranges like for example <literal>YEAR TO MINUTE</> so you won't
   find support in ecpg for that either.
  </para>

  <sect2>
   <title>Additional types</title>
   <para>
    The Informix-special "string" pseudo-type for storing right-trimmed character string data is now
    supported in Informix-mode without using <literal>typedef</literal>. In fact, in Informix-mode,
    ECPG refuses to process source files that contain <literal>typedef sometype string;</literal>
<programlisting>
    EXEC SQL BEGIN DECLARE SECTION;
    string userid; /* this variable will contain trimmed data */
    EXEC SQL END DECLARE SECTION;

    EXEC SQL FETCH MYCUR INTO :userid;
</programlisting>
   </para>
  </sect2>

  <sect2>
   <title>Additional/missing embedded SQL statements</title>
   <para>
    <variablelist>
     <varlistentry>
      <term><literal>CLOSE DATABASE</></term>
      <listitem>
       <para>
        This statement closes the current connection. In fact, this is a
        synonym for ecpg's <literal>DISCONNECT CURRENT</>.:
<programlisting>
    $CLOSE DATABASE;                /* close the current connection */
    EXEC SQL CLOSE DATABASE;
</programlisting>
       </para>
      </listitem>
     </varlistentry>
     <varlistentry>
      <term><literal>FREE cursor_name</></term>
      <listitem>
       <para>
        Due to the differences how ECPG works compared to Informix's ESQL/C (i.e. which steps
        are purely grammar transformations and which steps rely on the underlying runtime library)
        there is no <literal>FREE cursor_name</> statement in ECPG. This is because in ECPG,
        <literal>DECLARE CURSOR</literal> doesn't translate to a function call into
        the runtime library that uses to the cursor name. This means that there's no runtime
        bookkeeping of SQL cursors in the ECPG runtime library, only in the PostgreSQL server.
       </para>
      </listitem>
     </varlistentry>
     <varlistentry>
      <term><literal>FREE statement_name</></term>
      <listitem>
       <para>
        <literal>FREE statement_name</> is a synonym for <literal>DEALLOCATE PREPARE statement_name</>.
       </para>      
      </listitem>   
     </varlistentry>
    </variablelist>
   </para>
  </sect2>

  <sect2>
   <title>Informix-compatible SQLDA Descriptor Areas</title>
   <para>
    Informix-compatible mode supports a different structure than the one described in
    <xref linkend="ecpg-sqlda-descriptors">. See below:
<programlisting>
struct sqlvar_compat
{
        short   sqltype;
        int     sqllen;
        char       *sqldata;
        short      *sqlind;
        char       *sqlname;
        char       *sqlformat;
        short   sqlitype;
        short   sqlilen;
        char       *sqlidata;
        int     sqlxid;
        char       *sqltypename;
        short   sqltypelen;
        short   sqlownerlen;
        short   sqlsourcetype;
        char       *sqlownername;
        int     sqlsourceid;

        char       *sqlilongdata;
        int     sqlflags;
        void       *sqlreserved;
};

struct sqlda_compat
{
        short           sqld;
        struct sqlvar_compat *sqlvar;
        char            desc_name[19];
        short           desc_occ;
        struct sqlda_compat *desc_next;
        void               *reserved;
};

typedef struct sqlvar_compat    sqlvar_t;
typedef struct sqlda_compat     sqlda_t;
</programlisting>
   </para>

   <para>
    The global properties are:
    <variablelist>  

     <varlistentry>
     <term><literal>sqld</></term>
      <listitem>
       <para>
        The number of fields in the <literal>SQLDA</> descriptor.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
     <term><literal>sqlvar</></term>   
      <listitem>
       <para>
        Pointer to the per-field properties.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
     <term><literal>desc_name</></term>
      <listitem>
       <para>
        Unused, filled with zerobytes.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
     <term><literal>desc_occ</></term>
      <listitem>
       <para>
        Size of the allocated structure.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
     <term><literal>desc_next</></term>
      <listitem>
       <para>
        Pointer to the next SQLDA structure if the resultset contains more than one records.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
     <term><literal>reserved</></term>
      <listitem>
       <para>
        Unused pointer, contains NULL. Kept for Informix-compatibility.
       </para>
      </listitem>
     </varlistentry>

    </variablelist>

    The per-field properties are below, they are stored in the <literal>sqlvar</literal> array:

    <variablelist>

     <varlistentry>
     <term><literal>sqltype</></term>
      <listitem>
       <para>
        Type of the field. Constants are in <literal>sqltypes.h</literal>
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
     <term><literal>sqllen</></term>
      <listitem>
       <para>
        Length of the field data.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
     <term><literal>sqldata</></term>
      <listitem>
       <para>
        Pointer to the field data. The pointer is of <literal>char *</literal> type,
        the data pointed by it is in a binary format. Example:
<programlisting>
    int intval; 

    switch (sqldata->sqlvar[i].sqltype)
    {
      case SQLINTEGER:
        intval = *(int *)sqldata->sqlvar[i].sqldata;
        break;
      ...
    }
</programlisting>
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
     <term><literal>sqlind</></term>
      <listitem>
       <para>
        Pointer to the NULL indicator. If returned by DESCRIBE or FETCH then it's always a valid pointer.
        If used as input for <literal>EXECUTE ... USING sqlda;</literal> then NULL-pointer value means   
        that the value for this field is non-NULL. Otherwise a valid pointer and <literal>sqlitype</literal>
        has to be properly set. Example:
<programlisting>
    if (*(int2 *)sqldata->sqlvar[i].sqlind != 0)
      printf("value is NULL\n");
</programlisting>
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
     <term><literal>sqlname</></term>
      <listitem>
       <para>
        Name of the field. 0-terminated string.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
     <term><literal>sqlformat</></term>
      <listitem>
       <para>
        Reserved in Informix, value of PQfformat() for the field.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
     <term><literal>sqlitype</></term>
      <listitem>
       <para>
        Type of the NULL indicator data. It's always SQLSMINT when returning data from the server.
        When the <literal>SQLDA</literal> is used for a parametrized query, the data is treated   
        according to the set type.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
     <term><literal>sqlilen</></term>
      <listitem>
       <para>
        Length of the NULL indicator data.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
     <term><literal>sqlxid</></term>
      <listitem>
       <para>
        Extended type of the field, result of PQftype().
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
     <term><literal>sqltypename</></term>
     <term><literal>sqltypelen</></term> 
     <term><literal>sqlownerlen</></term>
     <term><literal>sqlsourcetype</></term>
     <term><literal>sqlownername</></term> 
     <term><literal>sqlsourceid</></term>  
     <term><literal>sqlflags</></term>     
     <term><literal>sqlreserved</></term>  
      <listitem>
       <para>
        Unused.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
     <term><literal>sqlilongdata</></term>
      <listitem>
       <para>
        It equals to <literal>sqldata</literal> if <literal>sqllen</literal> is larger than 32KB.
       </para>
      </listitem>
     </varlistentry>

    </variablelist>

    Example:
<programlisting>
EXEC SQL INCLUDE sqlda.h;

    sqlda_t        *sqlda; /* This doesn't need to be under embedded DECLARE SECTION */

    EXEC SQL BEGIN DECLARE SECTION;
    char *prep_stmt = "select * from table1";
    int i;
    EXEC SQL END DECLARE SECTION;

    ...

    EXEC SQL PREPARE mystmt FROM :prep_stmt;

    EXEC SQL DESCRIBE mystmt INTO sqlda;

    printf("# of fields: %d\n", sqlda-&gt;sqld);
    for (i = 0; i &lt; sqlda-&gt;sqld; i++)
      printf("field %d: \"%s\"\n", sqlda-&gt;sqlvar[i]-&gt;sqlname);

    EXEC SQL DECLARE mycursor CURSOR FOR mystmt;
    EXEC SQL OPEN mycursor;
    EXEC SQL WHENEVER NOT FOUND GOTO out;

    while (1)
    {
      EXEC SQL FETCH mycursor USING sqlda;
    }

    EXEC SQL CLOSE mycursor;

    free(sqlda); /* The main structure is all to be free(),
                  * sqlda and sqlda-&gt;sqlvar is in one allocated area */
</programlisting>
    For more information, see the <literal>sqlda.h</> header and the
    <literal>src/interfaces/ecpg/test/compat_informix/sqlda.pgc</literal> regression test.
   </para>
  </sect2>

  <sect2>
   <title>Additional functions</title>
   <para>
    <variablelist>
     <varlistentry>
      <term><function>decadd</></term>
      <listitem>
       <para>
        Add two decimal type values.
<synopsis>
int decadd(decimal *arg1, decimal *arg2, decimal *sum);
</synopsis>
        The function receives a pointer to the first operand of type decimal
        (<literal>arg1</>), a pointer to the second operand of type decimal
        (<literal>arg2</>) and a pointer to a value of type decimal that will
        contain the sum (<literal>sum</>). On success, the function returns 0.
        ECPG_INFORMIX_NUM_OVERFLOW is returned in case of overflow and 
        ECPG_INFORMIX_NUM_UNDERFLOW in case of underflow. -1 is returned for
        other failures and errno is set to the respective errno number of the
        pgtypeslib.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><function>deccmp</></term>
      <listitem>
       <para>
        Compare two variables of type decimal.
<synopsis>
int deccmp(decimal *arg1, decimal *arg2);
</synopsis>
        The function receives a pointer to the first decimal value
        (<literal>arg1</>), a pointer to the second decimal value
        (<literal>arg2</>) and returns an integer value that indicates which is
        the bigger value.
        <itemizedlist>
         <listitem>
          <para>
           1, if the value that <literal>arg1</> points to is bigger than the
           value that <literal>var2</> points to
          </para>
         </listitem>
         <listitem>
          <para>
           -1, if the value that <literal>arg1</> points to is smaller than the
           value that <literal>arg2</> points to </para>
         </listitem>
         <listitem>
          <para>
           0, if the value that <literal>arg1</> points to and the value that
           <literal>arg2</> points to are equal
          </para>
         </listitem>
        </itemizedlist>
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><function>deccopy</></term>
      <listitem>
       <para>
        Copy a decimal value.
<synopsis>
void deccopy(decimal *src, decimal *target);
</synopsis>
        The function receives a pointer to the decimal value that should be
        copied as the first argument (<literal>src</>) and a pointer to the
        target structure of type decimal (<literal>target</>) as the second
        argument.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><function>deccvasc</></term>
      <listitem>
       <para>
        Convert a value from its ASCII representation into a decimal type.
<synopsis>
int deccvasc(char *cp, int len, decimal *np);
</synopsis>
        The function receives a pointer to string that contains the string
        representation of the number to be converted (<literal>cp</>) as well
        as its length <literal>len</>. <literal>np</> is a pointer to the
        decimal value that saves the result of the operation.
       </para>
       <para>
        Valid formats are for example:
         <literal>-2</literal>,
         <literal>.794</literal>,
         <literal>+3.44</literal>,
         <literal>592.49E07</literal> or
         <literal>-32.84e-4</literal>.
       </para>
       <para>
        The function returns 0 on success. If overflow or underflow occurred,
        <literal>ECPG_INFORMIX_NUM_OVERFLOW</> or
        <literal>ECPG_INFORMIX_NUM_UNDERFLOW</> is returned. If the ASCII
        representation could not be parsed,
        <literal>ECPG_INFORMIX_BAD_NUMERIC</> is returned or
        <literal>ECPG_INFORMIX_BAD_EXPONENT</> if this problem occurred while
        parsing the exponent.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><function>deccvdbl</></term>
      <listitem>
       <para>
        Convert a value of type double to a value of type decimal.
<synopsis>
int deccvdbl(double dbl, decimal *np);
</synopsis>
        The function receives the variable of type double that should be
        converted as its first argument (<literal>dbl</>). As the second
        argument (<literal>np</>), the function receives a pointer to the
        decimal variable that should hold the result of the operation.
       </para>
       <para>
        The function returns 0 on success and a negative value if the
        conversion failed.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><function>deccvint</></term>
      <listitem>
       <para>
        Convert a value of type int to a value of type decimal.
<synopsis>
int deccvint(int in, decimal *np);
</synopsis>
        The function receives the variable of type int that should be
        converted as its first argument (<literal>in</>). As the second
        argument (<literal>np</>), the function receives a pointer to the
        decimal variable that should hold the result of the operation.
       </para>
       <para>
        The function returns 0 on success and a negative value if the
        conversion failed.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><function>deccvlong</></term>
      <listitem>
       <para>
        Convert a value of type long to a value of type decimal.
<synopsis>
int deccvlong(long lng, decimal *np);
</synopsis>
        The function receives the variable of type long that should be
        converted as its first argument (<literal>lng</>). As the second
        argument (<literal>np</>), the function receives a pointer to the
        decimal variable that should hold the result of the operation.
       </para>
       <para>
        The function returns 0 on success and a negative value if the
        conversion failed.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><function>decdiv</></term>
      <listitem>
       <para>
        Divide two variables of type decimal.
<synopsis>
int decdiv(decimal *n1, decimal *n2, decimal *result);
</synopsis>
        The function receives pointers to the variables that are the first
        (<literal>n1</>) and the second (<literal>n2</>) operands and
        calculates <literal>n1</>/<literal>n2</>. <literal>result</> is a
        pointer to the variable that should hold the result of the operation.
       </para>
       <para>
        On success, 0 is returned and a negative value if the division fails.
        If overflow or underflow occurred, the function returns
        <literal>ECPG_INFORMIX_NUM_OVERFLOW</> or
        <literal>ECPG_INFORMIX_NUM_UNDERFLOW</> respectively. If an attempt to
        divide by zero is observed, the function returns
        <literal>ECPG_INFORMIX_DIVIDE_ZERO</literal>.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><function>decmul</></term>
      <listitem>
       <para>
        Multiply two decimal values.
<synopsis>
int decmul(decimal *n1, decimal *n2, decimal *result);
</synopsis>
        The function receives pointers to the variables that are the first
        (<literal>n1</>) and the second (<literal>n2</>) operands and
        calculates <literal>n1</>*<literal>n2</>. <literal>result</> is a
        pointer to the variable that should hold the result of the operation.
       </para>
       <para>
        On success, 0 is returned and a negative value if the multiplication
        fails. If overflow or underflow occurred, the function returns
        <literal>ECPG_INFORMIX_NUM_OVERFLOW</> or
        <literal>ECPG_INFORMIX_NUM_UNDERFLOW</> respectively.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><function>decsub</></term>
      <listitem>
       <para>
        Subtract one decimal value from another.
<synopsis>
int decsub(decimal *n1, decimal *n2, decimal *result);
</synopsis>
        The function receives pointers to the variables that are the first
        (<literal>n1</>) and the second (<literal>n2</>) operands and
        calculates <literal>n1</>-<literal>n2</>. <literal>result</> is a
        pointer to the variable that should hold the result of the operation.
       </para>
       <para>
        On success, 0 is returned and a negative value if the subtraction
        fails. If overflow or underflow occurred, the function returns
        <literal>ECPG_INFORMIX_NUM_OVERFLOW</> or
        <literal>ECPG_INFORMIX_NUM_UNDERFLOW</> respectively.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><function>dectoasc</></term>
      <listitem>
       <para>
        Convert a variable of type decimal to its ASCII representation in a C
        char* string.
<synopsis>
int dectoasc(decimal *np, char *cp, int len, int right)
</synopsis>
        The function receives a pointer to a variable of type decimal
        (<literal>np</>) that it converts to its textual representation.
        <literal>cp</> is the buffer that should hold the result of the
        operation. The parameter <literal>right</> specifies, how many digits
        right of the decimal point should be included in the output. The result
        will be rounded to this number of decimal digits. Setting
        <literal>right</> to -1 indicates that all available decimal digits
        should be included in the output. If the length of the output buffer,
        which is indicated by <literal>len</> is not sufficient to hold the
        textual representation including the trailing NUL character, only a
        single <literal>*</> character is stored in the result and -1 is
        returned.
       </para>
       <para>
        The function returns either -1 if the buffer <literal>cp</> was too
        small or <literal>ECPG_INFORMIX_OUT_OF_MEMORY</> if memory was
        exhausted. 
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><function>dectodbl</></term>
      <listitem>
       <para>
        Convert a variable of type decimal to a double.
<synopsis>
int dectodbl(decimal *np, double *dblp);
</synopsis>
        The function receives a pointer to the decimal value to convert
        (<literal>np</>) and a pointer to the double variable that
        should hold the result of the operation (<literal>dblp</>).
       </para>
       <para>
        On success, 0 is returned and a negative value if the conversion
        failed.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><function>dectoint</></term>
      <listitem>
       <para>
        Convert a variable to type decimal to an integer.
<synopsis>
int dectoint(decimal *np, int *ip);
</synopsis>
        The function receives a pointer to the decimal value to convert
        (<literal>np</>) and a pointer to the integer variable that
        should hold the result of the operation (<literal>ip</>).
       </para>
       <para>
        On success, 0 is returned and a negative value if the conversion
        failed. If an overflow occurred, <literal>ECPG_INFORMIX_NUM_OVERFLOW</>
        is returned.
       </para>
       <para>
        Note that the ecpg implementation differs from the <productname>Informix</productname>
        implementation. <productname>Informix</productname> limits an integer to the range from -32767 to
        32767, while the limits in the ecpg implementation depend on the
        architecture (<literal>-INT_MAX .. INT_MAX</>).
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><function>dectolong</></term>
      <listitem>
       <para>
        Convert a variable to type decimal to a long integer.
<synopsis>
int dectolong(decimal *np, long *lngp);
</synopsis>
        The function receives a pointer to the decimal value to convert
        (<literal>np</>) and a pointer to the long variable that
        should hold the result of the operation (<literal>lngp</>).
       </para>
       <para>
        On success, 0 is returned and a negative value if the conversion
        failed. If an overflow occurred, <literal>ECPG_INFORMIX_NUM_OVERFLOW</>
        is returned.
       </para>
       <para>
        Note that the ecpg implementation differs from the <productname>Informix</productname>
        implementation. <productname>Informix</productname> limits a long integer to the range from
        -2,147,483,647 to 2,147,483,647, while the limits in the ecpg
        implementation depend on the architecture (<literal>-LONG_MAX ..
        LONG_MAX</>).
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><function>rdatestr</></term>
      <listitem>
       <para>
        Converts a date to a C char* string.
<synopsis>
int rdatestr(date d, char *str);
</synopsis>
        The function receives two arguments, the first one is the date to
        convert (<literal>d</> and the second one is a pointer to the target
        string. The output format is always <literal>yyyy-mm-dd</>, so you need
        to allocate at least 11 bytes (including the NUL-terminator) for the
        string.
       </para>
       <para>
        The function returns 0 on success and a negative value in case of
        error.
       </para>
       <para>
        Note that ecpg's implementation differs from the <productname>Informix</productname>
        implementation. In <productname>Informix</productname> the format can be influenced by setting
        environment variables. In ecpg however, you cannot change the output
        format.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><function>rstrdate</></term>
      <listitem>
       <para>
        Parse the textual representation of a date.
<synopsis>
int rstrdate(char *str, date *d);
</synopsis>
        The function receives the textual representation of the date to convert
        (<literal>str</>) and a pointer to a variable of type date
        (<literal>d</>). This function does not allow you to specify a format
        mask. It uses the default format mask of <productname>Informix</productname> which is
        <literal>mm/dd/yyyy</>. Internally, this function is implemented by
        means of <function>rdefmtdate</>. Therefore, <function>rstrdate</> is
        not faster and if you have the choice you should opt for
        <function>rdefmtdate</> which allows you to specify the format mask
        explicitly.
       </para>
       <para>
        The function returns the same values as <function>rdefmtdate</>.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><function>rtoday</></term>
      <listitem>
       <para>
        Get the current date.
<synopsis>
void rtoday(date *d);
</synopsis>
        The function receives a pointer to a date variable (<literal>d</>)
        that it sets to the current date.
       </para>
       <para>
        Internally this function uses the <xref linkend="PGTYPESdatetoday">
        function.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><function>rjulmdy</></term>
      <listitem>
       <para>
        Extract the values for the day, the month and the year from a variable
        of type date.
<synopsis>
int rjulmdy(date d, short mdy[3]);
</synopsis>
        The function receives the date <literal>d</> and a pointer to an array
        of 3 short integer values <literal>mdy</>. The variable name indicates
        the sequential order: <literal>mdy[0]</> will be set to contain the
        number of the month, <literal>mdy[1]</> will be set to the value of the
        day and <literal>mdy[2]</> will contain the year.
       </para>
       <para>
        The function always returns 0 at the moment.
       </para>
       <para>
        Internally the function uses the <xref linkend="PGTYPESdatejulmdy">
        function.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><function>rdefmtdate</></term>
      <listitem>
       <para>
        Use a format mask to convert a character string to a value of type
        date.
<synopsis>
int rdefmtdate(date *d, char *fmt, char *str);
</synopsis>
        The function receives a pointer to the date value that should hold the
        result of the operation (<literal>d</>), the format mask to use for
        parsing the date (<literal>fmt</>) and the C char* string containing
        the textual representation of the date (<literal>str</>). The textual
        representation is expected to match the format mask. However you do not
        need to have a 1:1 mapping of the string to the format mask. The
        function only analyzes the sequential order and looks for the literals
        <literal>yy</literal> or <literal>yyyy</literal> that indicate the
        position of the year, <literal>mm</literal> to indicate the position of
        the month and <literal>dd</literal> to indicate the position of the
        day.
       </para>
       <para>
        The function returns the following values:
        <itemizedlist>
         <listitem>
          <para>
           0 - The function terminated successfully.
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>ECPG_INFORMIX_ENOSHORTDATE</> - The date does not contain
           delimiters between day, month and year. In this case the input
           string must be exactly 6 or 8 bytes long but isn't.
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>ECPG_INFORMIX_ENOTDMY</> - The format string did not
           correctly indicate the sequential order of year, month and day.
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>ECPG_INFORMIX_BAD_DAY</> - The input string does not
           contain a valid day.
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>ECPG_INFORMIX_BAD_MONTH</> - The input string does not
           contain a valid month.
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>ECPG_INFORMIX_BAD_YEAR</> - The input string does not
           contain a valid year.
          </para>
         </listitem>
        </itemizedlist>
       </para>
       <para>
        Internally this function is implemented to use the <xref
        linkend="PGTYPESdatedefmtasc"> function. See the reference there for a
        table of example input.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><function>rfmtdate</></term>
      <listitem>
       <para>
        Convert a variable of type date to its textual representation using a
        format mask.
<synopsis>
int rfmtdate(date d, char *fmt, char *str);
</synopsis>
        The function receives the date to convert (<literal>d</>), the format
        mask (<literal>fmt</>) and the string that will hold the textual
        representation of the date (<literal>str</>).
       </para>
       <para>
        On success, 0 is returned and a negative value if an error occurred.
       </para>
       <para>
        Internally this function uses the <xref linkend="PGTYPESdatefmtasc">
        function, see the reference there for examples.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><function>rmdyjul</></term>
      <listitem>
       <para>
        Create a date value from an array of 3 short integers that specify the
        day, the month and the year of the date.
<synopsis>
int rmdyjul(short mdy[3], date *d);
</synopsis>
        The function receives the array of the 3 short integers
        (<literal>mdy</>) and a pointer to a variable of type date that should
        hold the result of the operation.
       </para>
       <para>
        Currently the function returns always 0.
       </para>
       <para>
        Internally the function is implemented to use the function <xref
        linkend="PGTYPESdatemdyjul">.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><function>rdayofweek</></term>
      <listitem>
       <para>
        Return a number representing the day of the week for a date value.
<synopsis>
int rdayofweek(date d);
</synopsis>
        The function receives the date variable <literal>d</> as its only
        argument and returns an integer that indicates the day of the week for
        this date.
        <itemizedlist>
         <listitem>
          <para>
           0 - Sunday
          </para>
         </listitem>
         <listitem>
          <para>
           1 - Monday
          </para>
         </listitem>
         <listitem>
          <para>
           2 - Tuesday
          </para>
         </listitem>
         <listitem>
          <para>
           3 - Wednesday
          </para>
         </listitem>
         <listitem>
          <para>
           4 - Thursday
          </para>
         </listitem>
         <listitem>
          <para>
           5 - Friday
          </para>
         </listitem>
         <listitem>
          <para>
           6 - Saturday
          </para>
         </listitem>
        </itemizedlist>
       </para>
       <para>
        Internally the function is implemented to use the function <xref
        linkend="PGTYPESdatedayofweek">.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><function>dtcurrent</></term>
      <listitem>
       <para>
        Retrieve the current timestamp.
<synopsis>
void dtcurrent(timestamp *ts);
</synopsis>
        The function retrieves the current timestamp and saves it into the
        timestamp variable that <literal>ts</> points to.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><function>dtcvasc</></term>
      <listitem>
       <para>
        Parses a timestamp from its textual representation
        into a timestamp variable.
<synopsis>
int dtcvasc(char *str, timestamp *ts);
</synopsis>
        The function receives the string to parse (<literal>str</>) and a
        pointer to the timestamp variable that should hold the result of the
        operation (<literal>ts</>).
       </para>
       <para>
        The function returns 0 on success and a negative value in case of
        error.
       </para>
       <para>
        Internally this function uses the <xref
        linkend="PGTYPEStimestampfromasc"> function. See the reference there
        for a table with example inputs.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><function>dtcvfmtasc</></term>
      <listitem>
       <para>
        Parses a timestamp from its textual representation
        using a format mask into a timestamp variable.
<synopsis>
dtcvfmtasc(char *inbuf, char *fmtstr, timestamp *dtvalue)
</synopsis>
        The function receives the string to parse (<literal>inbuf</>), the
        format mask to use (<literal>fmtstr</>) and a pointer to the timestamp
        variable that should hold the result of the operation (<literal>ts</>).
       </para>
       <para>
        This functions is implemented by means of the <xref
        linkend="PGTYPEStimestampdefmtasc">. See the documentation
        there for a list of format specifiers that can be used.
       </para>
       <para>
        The function returns 0 on success and a negative value in case of
        error.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><function>dtsub</></term>
      <listitem>
       <para>
        Subtract one timestamp from another and return a variable of type
        interval.
<synopsis>
int dtsub(timestamp *ts1, timestamp *ts2, interval *iv);
</synopsis>
        The function will subtract the timestamp variable that <literal>ts2</>
        points to from the timestamp variable that <literal>ts1</> points to
        and will store the result in the interval variable that <literal>iv</>
        points to.
       </para>
       <para>
        Upon success, the function returns 0 and a negative value if an
        error occurred.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><function>dttoasc</></term>
      <listitem>
       <para>
        Convert a timestamp variable to a C char* string.
<synopsis>
int dttoasc(timestamp *ts, char *output);
</synopsis>
        The function receives a pointer to the timestamp variable to convert
        (<literal>ts</>) and the string that should hold the result of the
        operation <literal>output</>). It converts <literal>ts</> to its
        textual representation according to the SQL standard, which is
        be <literal>YYYY-MM-DD HH:MM:SS</literal>.
       </para>
       <para>
        Upon success, the function returns 0 and a negative value if an
        error occurred.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><function>dttofmtasc</></term>
      <listitem>
       <para>
        Convert a timestamp variable to a C char* using a format mask.
<synopsis>
int dttofmtasc(timestamp *ts, char *output, int str_len, char *fmtstr);
</synopsis>
        The function receives a pointer to the timestamp to convert as its
        first argument (<literal>ts</>), a pointer to the output buffer
        (<literal>output</>), the maximal length that has been allocated for
        the output buffer (<literal>str_len</literal>) and the format mask to
        use for the conversion (<literal>fmtstr</literal>).
       </para>
       <para>
        Upon success, the function returns 0 and a negative value if an
        error occurred.
       </para>
       <para>
        Internally, this function uses the <xref
        linkend="PGTYPEStimestampfmtasc"> function. See the reference there for
        information on what format mask specifiers can be used.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><function>intoasc</></term>
      <listitem>
       <para>
        Convert an interval variable to a C char* string.
<synopsis>
int intoasc(interval *i, char *str);
</synopsis>
        The function receives a pointer to the interval variable to convert
        (<literal>i</>) and the string that should hold the result of the
        operation <literal>str</>). It converts <literal>i</> to its
        textual representation according to the SQL standard, which is
        be <literal>YYYY-MM-DD HH:MM:SS</literal>.
       </para>
       <para>
        Upon success, the function returns 0 and a negative value if an
        error occurred.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><function>rfmtlong</></term>
      <listitem>
       <para>
        Convert a long integer value to its textual representation using a
        format mask.
<synopsis>
int rfmtlong(long lng_val, char *fmt, char *outbuf);
</synopsis>
        The function receives the long value <literal>lng_val</>, the format
        mask <literal>fmt</> and a pointer to the output buffer
        <literal>outbuf</>. It converts the long value according to the format
        mask to its textual representation.
       </para>
       <para>
        The format mask can be composed of the following format specifying
        characters:
        <itemizedlist>
         <listitem>
          <para>
           <literal>*</literal> (asterisk) - if this position would be blank
           otherwise, fill it with an asterisk.
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>&amp;</literal> (ampersand) - if this position would be
           blank otherwise, fill it with a zero.
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>#</literal> - turn leading zeroes into blanks.
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>&lt;</literal> - left-justify the number in the string.
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>,</literal> (comma) - group numbers of four or more digits
           into groups of three digits separated by a comma.
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>.</literal> (period) - this character separates the
           whole-number part of the number from the fractional part.
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>-</literal> (minus) - the minus sign appears if the number
           is a negative value.
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>+</literal> (plus) - the plus sign appears if the number is
           a positive value.
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>(</literal> - this replaces the minus sign in front of the
           negative number. The minus sign will not appear.
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>)</literal> - this character replaces the minus and is
           printed behind the negative value.
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>$</literal> - the currency symbol.
          </para>
         </listitem>
        </itemizedlist>
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><function>rupshift</></term>
      <listitem>
       <para>
        Convert a string to upper case.
<synopsis>
void rupshift(char *str);
</synopsis>
        The function receives a pointer to the string and transforms every
        lower case character to upper case.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><function>byleng</></term>
      <listitem>
       <para>
        Return the number of characters in a string without counting trailing
        blanks.
<synopsis>
int byleng(char *str, int len);
</synopsis>
        The function expects a fixed-length string as its first argument
        (<literal>str</>) and its length as its second argument
        (<literal>len</>). It returns the number of significant characters,
        that is the length of the string without trailing blanks.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><function>ldchar</></term>
      <listitem>
       <para>
        Copy a fixed-length string into a null-terminated string.
<synopsis>
void ldchar(char *src, int len, char *dest);
</synopsis>
        The function receives the fixed-length string to copy
        (<literal>src</>), its length (<literal>len</>) and a pointer to the
        destination memory (<literal>dest</>). Note that you need to reserve at
        least <literal>len+1</> bytes for the string that <literal>dest</>
        points to. The function copies at most <literal>len</> bytes to the new
        location (less if the source string has trailing blanks) and adds the
        null-terminator.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><function>rgetmsg</></term>
      <listitem>
       <para>
<synopsis>
int rgetmsg(int msgnum, char *s, int maxsize);
</synopsis>
        This function exists but is not implemented at the moment!
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><function>rtypalign</></term>
      <listitem>
       <para>
<synopsis>
int rtypalign(int offset, int type);
</synopsis>
        This function exists but is not implemented at the moment!
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><function>rtypmsize</></term>
      <listitem>
       <para>
<synopsis>
int rtypmsize(int type, int len);
</synopsis>
        This function exists but is not implemented at the moment!
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><function>rtypwidth</></term>
      <listitem>
       <para>
<synopsis>
int rtypwidth(int sqltype, int sqllen);
</synopsis>
        This function exists but is not implemented at the moment!
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="rsetnull">
      <term><function>rsetnull</></term>
      <listitem>
       <para>
        Set a variable to NULL.
<synopsis>
int rsetnull(int t, char *ptr);
</synopsis>
        The function receives an integer that indicates the type of the
        variable and a pointer to the variable itself that is casted to a C
        char* pointer.
       </para>
       <para>
        The following types exist:
        <itemizedlist>
         <listitem>
          <para>
           <literal>CCHARTYPE</literal> - For a variable of type <type>char</type> or <type>char*</type>
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>CSHORTTYPE</literal> - For a variable of type <type>short int</type>
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>CINTTYPE</literal> - For a variable of type <type>int</type>
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>CBOOLTYPE</literal> - For a variable of type <type>boolean</type>
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>CFLOATTYPE</literal> - For a variable of type <type>float</type>
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>CLONGTYPE</literal> - For a variable of type <type>long</type>
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>CDOUBLETYPE</literal> - For a variable of type <type>double</type>
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>CDECIMALTYPE</literal> - For a variable of type <type>decimal</type>
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>CDATETYPE</literal> - For a variable of type <type>date</type>
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>CDTIMETYPE</literal> - For a variable of type <type>timestamp</type>
          </para>
         </listitem>
        </itemizedlist>
       </para>

       <para>
        Here is an example of a call to this function:
<programlisting><![CDATA[
$char c[] = "abc       ";
$short s = 17;
$int i = -74874;

rsetnull(CCHARTYPE, (char *) c);
rsetnull(CSHORTTYPE, (char *) &s);
rsetnull(CINTTYPE, (char *) &i);
]]>
</programlisting>
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><function>risnull</></term>
      <listitem>
       <para>
        Test if a variable is NULL.
<synopsis>
int risnull(int t, char *ptr);
</synopsis>
        The function receives the type of the variable to test (<literal>t</>)
        as well a pointer to this variable (<literal>ptr</>). Note that the
        latter needs to be casted to a char*. See the function <xref
        linkend="rsetnull"> for a list of possible variable types.
       </para>
       <para>
        Here is an example of how to use this function:
<programlisting><![CDATA[
$char c[] = "abc       ";
$short s = 17;
$int i = -74874;

risnull(CCHARTYPE, (char *) c);
risnull(CSHORTTYPE, (char *) &s);
risnull(CINTTYPE, (char *) &i);
]]>
</programlisting>
       </para>
      </listitem>
     </varlistentry>
    </variablelist>
   </para>
  </sect2>

  <sect2>
   <title>Additional constants</title>
   <para>
    Note that all constants here describe errors and all of them are defined
    to represent negative values. In the descriptions of the different
    constants you can also find the value that the constants represent in the
    current implementation. However you should not rely on this number. You can
    however rely on the fact all of them are defined to represent negative
    values.
    <variablelist>
     <varlistentry>
      <term><literal>ECPG_INFORMIX_NUM_OVERFLOW</></term>
      <listitem>
       <para>
        Functions return this value if an overflow occurred in a
        calculation. Internally it is defined to -1200 (the <productname>Informix</productname>
        definition).
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>ECPG_INFORMIX_NUM_UNDERFLOW</></term>
      <listitem>
       <para>
        Functions return this value if an underflow occurred in a calculation.
        Internally it is defined to -1201 (the <productname>Informix</productname> definition).
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>ECPG_INFORMIX_DIVIDE_ZERO</></term>
      <listitem>
       <para>
        Functions return this value if an attempt to divide by zero is
        observed. Internally it is defined to -1202 (the <productname>Informix</productname> definition).
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>ECPG_INFORMIX_BAD_YEAR</></term>
      <listitem>
       <para>
        Functions return this value if a bad value for a year was found while
        parsing a date. Internally it is defined to -1204 (the <productname>Informix</productname>
        definition).
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>ECPG_INFORMIX_BAD_MONTH</></term>
      <listitem>
       <para>
        Functions return this value if a bad value for a month was found while
        parsing a date. Internally it is defined to -1205 (the <productname>Informix</productname>
        definition).
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>ECPG_INFORMIX_BAD_DAY</></term>
      <listitem>
       <para>
        Functions return this value if a bad value for a day was found while
        parsing a date. Internally it is defined to -1206 (the <productname>Informix</productname>
        definition).
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>ECPG_INFORMIX_ENOSHORTDATE</></term>
      <listitem>
       <para>
        Functions return this value if a parsing routine needs a short date
        representation but did not get the date string in the right length.
        Internally it is defined to -1209 (the <productname>Informix</productname> definition).
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>ECPG_INFORMIX_DATE_CONVERT</></term>
      <listitem>
       <para>
        Functions return this value if Internally it is defined to -1210 (the
        <productname>Informix</productname> definition).
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>ECPG_INFORMIX_OUT_OF_MEMORY</></term>
      <listitem>
       <para>
        Functions return this value if Internally it is defined to -1211 (the
        <productname>Informix</productname> definition).
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>ECPG_INFORMIX_ENOTDMY</></term>
      <listitem>
       <para>
        Functions return this value if a parsing routine was supposed to get a
        format mask (like <literal>mmddyy</>) but not all fields were listed
        correctly. Internally it is defined to -1212 (the <productname>Informix</productname> definition).
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>ECPG_INFORMIX_BAD_NUMERIC</></term>
      <listitem>
       <para>
        Functions return this value either if a parsing routine cannot parse
        the textual representation for a numeric value because it contains
        errors or if a routine cannot complete a calculation involving numeric
        variables because at least one of the numeric variables is invalid.
        Internally it is defined to -1213 (the <productname>Informix</productname> definition).
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>ECPG_INFORMIX_BAD_EXPONENT</></term>
      <listitem>
       <para>
        Functions return this value if Internally it is defined to -1216 (the
        <productname>Informix</productname> definition).
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>ECPG_INFORMIX_BAD_DATE</></term>
      <listitem>
       <para>
        Functions return this value if Internally it is defined to -1218 (the
        <productname>Informix</productname> definition).
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>ECPG_INFORMIX_EXTRA_CHARS</></term>
      <listitem>
       <para>
        Functions return this value if Internally it is defined to -1264 (the
        <productname>Informix</productname> definition).
       </para>
      </listitem>
     </varlistentry>
    </variablelist>
   </para>
  </sect2>
 </sect1>

 <sect1 id="ecpg-errors">
  <title>Error Handling</title>

  <para>
   This section describes how you can handle exceptional conditions
   and warnings in an embedded SQL program.  There are several
   nonexclusive facilities for this.
  </para>

  <sect2>
   <title>Setting Callbacks</title>

   <para>
    One simple method to catch errors and warnings is to set a
    specific action to be executed whenever a particular condition
    occurs.  In general:
<programlisting>
EXEC SQL WHENEVER <replaceable>condition</replaceable> <replaceable>action</replaceable>;
</programlisting>
   </para>

   <para>
    <replaceable>condition</replaceable> can be one of the following:

    <variablelist>
     <varlistentry>
      <term><literal>SQLERROR</literal></term>
      <listitem>
       <para>
        The specified action is called whenever an error occurs during
        the execution of an SQL statement.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>SQLWARNING</literal></term>
      <listitem>
       <para>
        The specified action is called whenever a warning occurs
        during the execution of an SQL statement.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>NOT FOUND</literal></term>
      <listitem>
       <para>
        The specified action is called whenever an SQL statement
        retrieves or affects zero rows.  (This condition is not an
        error, but you might be interested in handling it specially.)
       </para>
      </listitem>
     </varlistentry>
    </variablelist>
   </para>

   <para>
    <replaceable>action</replaceable> can be one of the following:

    <variablelist>
     <varlistentry>
      <term><literal>CONTINUE</literal></term>
      <listitem>
       <para>
        This effectively means that the condition is ignored.  This is
        the default.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>GOTO <replaceable>label</replaceable></literal></term>
      <term><literal>GO TO <replaceable>label</replaceable></literal></term>
      <listitem>
       <para>
        Jump to the specified label (using a C <literal>goto</literal>
        statement).
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>SQLPRINT</literal></term>
      <listitem>
       <para>
        Print a message to standard error.  This is useful for simple
        programs or during prototyping.  The details of the message
        cannot be configured.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>STOP</literal></term>
      <listitem>
       <para>
        Call <literal>exit(1)</literal>, which will terminate the
        program.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>DO BREAK</literal></term>
      <listitem>
       <para>
        Execute the C statement <literal>break</literal>.  This should
        only be used in loops or <literal>switch</literal> statements.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>CALL <replaceable>name</replaceable> (<replaceable>args</replaceable>)</literal></term>
      <term><literal>DO <replaceable>name</replaceable> (<replaceable>args</replaceable>)</literal></term>
      <listitem>
       <para>
        Call the specified C functions with the specified arguments.
       </para>
      </listitem>
     </varlistentry>
    </variablelist>

    The SQL standard only provides for the actions
    <literal>CONTINUE</literal> and <literal>GOTO</literal> (and
    <literal>GO TO</literal>).
   </para>

   <para>
    Here is an example that you might want to use in a simple program.
    It prints a simple message when a warning occurs and aborts the
    program when an error happens:
<programlisting>
EXEC SQL WHENEVER SQLWARNING SQLPRINT;
EXEC SQL WHENEVER SQLERROR STOP;
</programlisting>
   </para>

   <para>
    The statement <literal>EXEC SQL WHENEVER</literal> is a directive
    of the SQL preprocessor, not a C statement.  The error or warning
    actions that it sets apply to all embedded SQL statements that
    appear below the point where the handler is set, unless a
    different action was set for the same condition between the first
    <literal>EXEC SQL WHENEVER</literal> and the SQL statement causing
    the condition, regardless of the flow of control in the C program.
    So neither of the two following C program excerpts will have the
    desired effect:
<programlisting>
/*
 * WRONG
 */
int main(int argc, char *argv[])
{
    ...
    if (verbose) {
        EXEC SQL WHENEVER SQLWARNING SQLPRINT;
    }
    ...
    EXEC SQL SELECT ...;
    ...
}
</programlisting>

<programlisting>
/*
 * WRONG
 */
int main(int argc, char *argv[])
{
    ...
    set_error_handler();
    ...
    EXEC SQL SELECT ...;
    ...
}

static void set_error_handler(void)
{
    EXEC SQL WHENEVER SQLERROR STOP;
}
</programlisting>
   </para>
  </sect2>

  <sect2>
   <title>sqlca</title>

   <para>
    For more powerful error handling, the embedded SQL interface
    provides a global variable with the name <varname>sqlca</varname>
    that has the following structure:
<programlisting>
struct
{
    char sqlcaid[8];
    long sqlabc;
    long sqlcode;
    struct
    {
        int sqlerrml;
        char sqlerrmc[SQLERRMC_LEN];
    } sqlerrm;
    char sqlerrp[8];
    long sqlerrd[6];
    char sqlwarn[8];
    char sqlstate[5];
} sqlca;
</programlisting>
    (In a multithreaded program, every thread automatically gets its
    own copy of <varname>sqlca</varname>.  This works similarly to the
    handling of the standard C global variable
    <varname>errno</varname>.)
   </para>

   <para>
    <varname>sqlca</varname> covers both warnings and errors.  If
    multiple warnings or errors occur during the execution of a
    statement, then <varname>sqlca</varname> will only contain
    information about the last one.
   </para>

   <para>
    If no error occurred in the last <acronym>SQL</acronym> statement,
    <literal>sqlca.sqlcode</literal> will be 0 and
    <literal>sqlca.sqlstate</literal> will be
    <literal>"00000"</literal>.  If a warning or error occurred, then
    <literal>sqlca.sqlcode</literal> will be negative and
    <literal>sqlca.sqlstate</literal> will be different from
    <literal>"00000"</literal>.  A positive
    <literal>sqlca.sqlcode</literal> indicates a harmless condition,
    such as that the last query returned zero rows.
    <literal>sqlcode</literal> and <literal>sqlstate</literal> are two
    different error code schemes; details appear below.
   </para>

   <para>
    If the last SQL statement was successful, then
    <literal>sqlca.sqlerrd[1]</literal> contains the OID of the
    processed row, if applicable, and
    <literal>sqlca.sqlerrd[2]</literal> contains the number of
    processed or returned rows, if applicable to the command.
   </para>

   <para>
    In case of an error or warning,
    <literal>sqlca.sqlerrm.sqlerrmc</literal> will contain a string
    that describes the error.  The field
    <literal>sqlca.sqlerrm.sqlerrml</literal> contains the length of
    the error message that is stored in
    <literal>sqlca.sqlerrm.sqlerrmc</literal> (the result of
    <function>strlen()</function>, not really interesting for a C
    programmer).  Note that some messages are too long to fit in the
    fixed-size <literal>sqlerrmc</literal> array; they will be truncated.
   </para>

   <para>
    In case of a warning, <literal>sqlca.sqlwarn[2]</literal> is set
    to <literal>W</literal>.  (In all other cases, it is set to
    something different from <literal>W</literal>.)  If
    <literal>sqlca.sqlwarn[1]</literal> is set to
    <literal>W</literal>, then a value was truncated when it was
    stored in a host variable.  <literal>sqlca.sqlwarn[0]</literal> is
    set to <literal>W</literal> if any of the other elements are set
    to indicate a warning.
   </para>

   <para>
    The fields <structfield>sqlcaid</structfield>,
    <structfield>sqlcabc</structfield>,
    <structfield>sqlerrp</structfield>, and the remaining elements of
    <structfield>sqlerrd</structfield> and
    <structfield>sqlwarn</structfield> currently contain no useful
    information.
   </para>

   <para>
    The structure <varname>sqlca</varname> is not defined in the SQL
    standard, but is implemented in several other SQL database
    systems.  The definitions are similar at the core, but if you want
    to write portable applications, then you should investigate the
    different implementations carefully.
   </para>
  </sect2>

  <sect2>
   <title><literal>SQLSTATE</literal> vs <literal>SQLCODE</literal></title>

   <para>
    The fields <literal>sqlca.sqlstate</literal> and
    <literal>sqlca.sqlcode</literal> are two different schemes that
    provide error codes.  Both are derived from the SQL standard, but
    <literal>SQLCODE</literal> has been marked deprecated in the SQL-92
    edition of the standard and has been dropped in later editions.
    Therefore, new applications are strongly encouraged to use
    <literal>SQLSTATE</literal>.
   </para>

   <para>
    <literal>SQLSTATE</literal> is a five-character array.  The five
    characters contain digits or upper-case letters that represent
    codes of various error and warning conditions.
    <literal>SQLSTATE</literal> has a hierarchical scheme: the first
    two characters indicate the general class of the condition, the
    last three characters indicate a subclass of the general
    condition.  A successful state is indicated by the code
    <literal>00000</literal>.  The <literal>SQLSTATE</literal> codes are for
    the most part defined in the SQL standard.  The
    <productname>PostgreSQL</productname> server natively supports
    <literal>SQLSTATE</literal> error codes; therefore a high degree
    of consistency can be achieved by using this error code scheme
    throughout all applications.  For further information see
    <xref linkend="errcodes-appendix">.
   </para>

   <para>
    <literal>SQLCODE</literal>, the deprecated error code scheme, is a
    simple integer.  A value of 0 indicates success, a positive value
    indicates success with additional information, a negative value
    indicates an error.  The SQL standard only defines the positive
    value +100, which indicates that the last command returned or
    affected zero rows, and no specific negative values.  Therefore,
    this scheme can only achieve poor portability and does not have a
    hierarchical code assignment.  Historically, the embedded SQL
    processor for <productname>PostgreSQL</productname> has assigned
    some specific <literal>SQLCODE</literal> values for its use, which
    are listed below with their numeric value and their symbolic name.
    Remember that these are not portable to other SQL implementations.
    To simplify the porting of applications to the
    <literal>SQLSTATE</literal> scheme, the corresponding
    <literal>SQLSTATE</literal> is also listed.  There is, however, no
    one-to-one or one-to-many mapping between the two schemes (indeed
    it is many-to-many), so you should consult the global
    <literal>SQLSTATE</literal> listing in <xref linkend="errcodes-appendix">
    in each case.
   </para>

   <para>
    These are the assigned <literal>SQLCODE</literal> values:

    <variablelist>
     <varlistentry>
      <term>-12 (<symbol>ECPG_OUT_OF_MEMORY</symbol>)</term>
      <listitem>
       <para>
        Indicates that your virtual memory is exhausted. (SQLSTATE
        YE001)
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term>-200 (<symbol>ECPG_UNSUPPORTED</symbol>)</term>
     <listitem>
      <para>
       Indicates the preprocessor has generated something that the
       library does not know about.  Perhaps you are running
       incompatible versions of the preprocessor and the
       library. (SQLSTATE YE002)
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term>-201 (<symbol>ECPG_TOO_MANY_ARGUMENTS</symbol>)</term>
     <listitem>
      <para>
       This means that the command specified more host variables than
       the command expected.  (SQLSTATE 07001 or 07002)
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term>-202 (<symbol>ECPG_TOO_FEW_ARGUMENTS</symbol>)</term>
     <listitem>
      <para>
       This means that the command specified fewer host variables than
       the command expected.  (SQLSTATE 07001 or 07002)
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term>-203 (<symbol>ECPG_TOO_MANY_MATCHES</symbol>)</term>
     <listitem>
      <para>
       This means a query has returned multiple rows but the statement
       was only prepared to store one result row (for example, because
       the specified variables are not arrays).  (SQLSTATE 21000)
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term>-204 (<symbol>ECPG_INT_FORMAT</symbol>)</term>
     <listitem>
      <para>
       The host variable is of type <type>int</type> and the datum in
       the database is of a different type and contains a value that
       cannot be interpreted as an <type>int</type>.  The library uses
       <function>strtol()</function> for this conversion.  (SQLSTATE
       42804)
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term>-205 (<symbol>ECPG_UINT_FORMAT</symbol>)</term>
     <listitem>
      <para>
       The host variable is of type <type>unsigned int</type> and the
       datum in the database is of a different type and contains a
       value that cannot be interpreted as an <type>unsigned
       int</type>.  The library uses <function>strtoul()</function>
       for this conversion.  (SQLSTATE 42804)
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term>-206 (<symbol>ECPG_FLOAT_FORMAT</symbol>)</term>
     <listitem>
      <para>
       The host variable is of type <type>float</type> and the datum
       in the database is of another type and contains a value that
       cannot be interpreted as a <type>float</type>.  The library
       uses <function>strtod()</function> for this conversion.
       (SQLSTATE 42804)
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term>-207 (<symbol>ECPG_CONVERT_BOOL</symbol>)</term>
     <listitem>
      <para>
       This means the host variable is of type <type>bool</type> and
       the datum in the database is neither <literal>'t'</> nor
       <literal>'f'</>.  (SQLSTATE 42804)
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term>-208 (<symbol>ECPG_EMPTY</symbol>)</term>
     <listitem>
      <para>
       The statement sent to the <productname>PostgreSQL</productname>
       server was empty.  (This cannot normally happen in an embedded
       SQL program, so it might point to an internal error.)  (SQLSTATE
       YE002)
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term>-209 (<symbol>ECPG_MISSING_INDICATOR</symbol>)</term>
     <listitem>
      <para>
       A null value was returned and no null indicator variable was
       supplied.  (SQLSTATE 22002)
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term>-210 (<symbol>ECPG_NO_ARRAY</symbol>)</term>
     <listitem>
      <para>
       An ordinary variable was used in a place that requires an
       array.  (SQLSTATE 42804)
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term>-211 (<symbol>ECPG_DATA_NOT_ARRAY</symbol>)</term>
     <listitem>
      <para>
       The database returned an ordinary variable in a place that
       requires array value.  (SQLSTATE 42804)
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term>-220 (<symbol>ECPG_NO_CONN</symbol>)</term>
     <listitem>
      <para>
       The program tried to access a connection that does not exist.
       (SQLSTATE 08003)
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term>-221 (<symbol>ECPG_NOT_CONN</symbol>)</term>
     <listitem>
      <para>
       The program tried to access a connection that does exist but is
       not open.  (This is an internal error.)  (SQLSTATE YE002)
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term>-230 (<symbol>ECPG_INVALID_STMT</symbol>)</term>
     <listitem>
      <para>
       The statement you are trying to use has not been prepared.
       (SQLSTATE 26000)
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term>-240 (<symbol>ECPG_UNKNOWN_DESCRIPTOR</symbol>)</term>
     <listitem>
      <para>
       The descriptor specified was not found.  The statement you are
       trying to use has not been prepared.  (SQLSTATE 33000)
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term>-241 (<symbol>ECPG_INVALID_DESCRIPTOR_INDEX</symbol>)</term>
     <listitem>
      <para>
       The descriptor index specified was out of range.  (SQLSTATE
       07009)
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term>-242 (<symbol>ECPG_UNKNOWN_DESCRIPTOR_ITEM</symbol>)</term>
     <listitem>
      <para>
       An invalid descriptor item was requested.  (This is an internal
       error.)  (SQLSTATE YE002)
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term>-243 (<symbol>ECPG_VAR_NOT_NUMERIC</symbol>)</term>
     <listitem>
      <para>
       During the execution of a dynamic statement, the database
       returned a numeric value and the host variable was not numeric.
       (SQLSTATE 07006)
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term>-244 (<symbol>ECPG_VAR_NOT_CHAR</symbol>)</term>
     <listitem>
      <para>
       During the execution of a dynamic statement, the database
       returned a non-numeric value and the host variable was numeric.
       (SQLSTATE 07006)
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term>-400 (<symbol>ECPG_PGSQL</symbol>)</term>
     <listitem>
      <para>
       Some error caused by the <productname>PostgreSQL</productname>
       server.  The message contains the error message from the
       <productname>PostgreSQL</productname> server.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term>-401 (<symbol>ECPG_TRANS</symbol>)</term>
     <listitem>
      <para>
       The <productname>PostgreSQL</productname> server signaled that
       we cannot start, commit, or rollback the transaction.
       (SQLSTATE 08007)
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term>-402 (<symbol>ECPG_CONNECT</symbol>)</term>
     <listitem>
      <para>
       The connection attempt to the database did not succeed.
       (SQLSTATE 08001)
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term>100 (<symbol>ECPG_NOT_FOUND</symbol>)</term>
     <listitem>
      <para>
       This is a harmless condition indicating that the last command
       retrieved or processed zero rows, or that you are at the end of
       the cursor.  (SQLSTATE 02000)
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>
  </sect2>
 </sect1>

 <sect1 id="ecpg-preproc">
  <title>Preprocessor directives</title>

  <sect2>
   <title>Including files</title>

   <para>
    To include an external file into your embedded SQL program, use:
<programlisting>
EXEC SQL INCLUDE <replaceable>filename</replaceable>;
</programlisting>
    The embedded SQL preprocessor will look for a file named
    <literal><replaceable>filename</replaceable>.h</literal>,
    preprocess it, and include it in the resulting C output.  Thus,
    embedded SQL statements in the included file are handled correctly.
   </para>

   <para>
    Note that this is <emphasis>not</emphasis> the same as:
<programlisting>
#include &lt;<replaceable>filename</replaceable>.h&gt;
</programlisting>
    because this file would not be subject to SQL command preprocessing.
    Naturally, you can continue to use the C
    <literal>#include</literal> directive to include other header
    files.
   </para>

   <note>
    <para>
     The include file name is case-sensitive, even though the rest of
     the <literal>EXEC SQL INCLUDE</literal> command follows the normal
     SQL case-sensitivity rules.
    </para>
   </note>
  </sect2>

  <sect2>
   <title>The #define and #undef directives</title>
   <para>
    Similar to the directive <literal>#define</literal> that is known from C,
    embedded SQL has a similar concept:
<programlisting>
EXEC SQL DEFINE <replaceable>name</>;
EXEC SQL DEFINE <replaceable>name</> <replaceable>value</>;
</programlisting>
    So you can define a name:
<programlisting>
EXEC SQL DEFINE HAVE_FEATURE;
</programlisting>
    And you can also define constants:
<programlisting>
EXEC SQL DEFINE MYNUMBER 12;
EXEC SQL DEFINE MYSTRING 'abc';
</programlisting>
    Use <literal>undef</> to remove a previous definition:
<programlisting>
EXEC SQL UNDEF MYNUMBER;
</programlisting>
   </para>

   <para>
    Of course you can continue to use the C versions <literal>#define</literal>
    and <literal>#undef</literal> in your embedded SQL program. The difference
    is where your defined values get evaluated. If you use <literal>EXEC SQL
    DEFINE</> then the ecpg preprocessor evaluates the defines and substitutes
    the values. For example if you write:
<programlisting>
EXEC SQL DEFINE MYNUMBER 12;
...
EXEC SQL UPDATE Tbl SET col = MYNUMBER;
</programlisting>
    then ecpg will already do the substitution and your C compiler will never
    see any name or identifier <literal>MYNUMBER</>. Note that you cannot use
    <literal>#define</literal> for a constant that you are going to use in an
    embedded SQL query because in this case the embedded SQL precompiler is not
    able to see this declaration.
   </para>
  </sect2>

  <sect2>
   <title>ifdef, ifndef, else, elif and endif directives</title>
   <para>
   You can use the following directives to compile code sections conditionally:

   <variablelist>
    <varlistentry>
     <term><literal>EXEC SQL ifdef <replaceable>name</>;</literal></term>
     <listitem>
     <para>
      Checks a <replaceable>name</> and processes subsequent lines if
      <replaceable>name</> has been created with <literal>EXEC SQL define
      <replaceable>name</></literal>.
     </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><literal>EXEC SQL ifndef <replaceable>name</>;</literal></term>
     <listitem>
     <para>
      Checks a <replaceable>name</> and processes subsequent lines if
      <replaceable>name</> has <emphasis>not</emphasis> been created with
      <literal>EXEC SQL define <replaceable>name</></literal>.
     </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><literal>EXEC SQL else;</literal></term>
     <listitem>
     <para>
      Starts processing an alternative section to a section introduced by
      either <literal>EXEC SQL ifdef <replaceable>name</></literal> or
      <literal>EXEC SQL ifndef <replaceable>name</></literal>.
     </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><literal>EXEC SQL elif <replaceable>name</>;</literal></term>
     <listitem>
     <para>
      Checks <replaceable>name</> and starts an alternative section if
      <replaceable>name</> has been created with <literal>EXEC SQL define
      <replaceable>name</></literal>.
     </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><literal>EXEC SQL endif;</literal></term>
     <listitem>
     <para>
      Ends an alternative section.
     </para>
     </listitem>
    </varlistentry>
   </variablelist>
   </para>

   <para>
    Example:
<programlisting>
   exec sql ifndef TZVAR;
   exec sql SET TIMEZONE TO 'GMT';
   exec sql elif TZNAME;
   exec sql SET TIMEZONE TO TZNAME;
   exec sql else;
   exec sql SET TIMEZONE TO TZVAR;
   exec sql endif;
</programlisting>
   </para>

  </sect2>
 </sect1>
 
  <sect1 id="ecpg-process">
  <title>Processing Embedded SQL Programs</title>

  <para>
   Now that you have an idea how to form embedded SQL C programs, you
   probably want to know how to compile them.  Before compiling you
   run the file through the embedded <acronym>SQL</acronym>
   <acronym>C</acronym> preprocessor, which converts the
   <acronym>SQL</acronym> statements you used to special function
   calls.  After compiling, you must link with a special library that
   contains the needed functions. These functions fetch information
   from the arguments, perform the <acronym>SQL</acronym> command using
   the <application>libpq</application> interface, and put the result
   in the arguments specified for output.
  </para>

  <para>
   The preprocessor program is called <filename>ecpg</filename> and is
   included in a normal <productname>PostgreSQL</> installation.
   Embedded SQL programs are typically named with an extension
   <filename>.pgc</filename>.  If you have a program file called
   <filename>prog1.pgc</filename>, you can preprocess it by simply
   calling:
<programlisting>
ecpg prog1.pgc
</programlisting>
   This will create a file called <filename>prog1.c</filename>.  If
   your input files do not follow the suggested naming pattern, you
   can specify the output file explicitly using the
   <option>-o</option> option.
  </para>

  <para>
   The preprocessed file can be compiled normally, for example:
<programlisting>
cc -c prog1.c
</programlisting>
   The generated C source files include header files from the
   <productname>PostgreSQL</> installation, so if you installed
   <productname>PostgreSQL</> in a location that is not searched by
   default, you have to add an option such as
   <literal>-I/usr/local/pgsql/include</literal> to the compilation
   command line.
  </para>

  <para>
   To link an embedded SQL program, you need to include the
   <filename>libecpg</filename> library, like so:
<programlisting>
cc -o myprog prog1.o prog2.o ... -lecpg
</programlisting>
   Again, you might have to add an option like
   <literal>-L/usr/local/pgsql/lib</literal> to that command line.
  </para>

  <para>
   If you manage the build process of a larger project using
   <application>make</application>, it might be convenient to include
   the following implicit rule to your makefiles:
<programlisting>
ECPG = ecpg

%.c: %.pgc
        $(ECPG) $&lt;
</programlisting>
  </para>

  <para>
   The complete syntax of the <command>ecpg</command> command is
   detailed in <xref linkend="app-ecpg">.
  </para>

  <para>
   The <application>ecpg</application> library is thread-safe by
   default.  However, you might need to use some threading
   command-line options to compile your client code.
  </para>
 </sect1>

 <sect1 id="ecpg-library">
  <title>Library Functions</title>

  <para>
   The <filename>libecpg</filename> library primarily contains
   <quote>hidden</quote> functions that are used to implement the
   functionality expressed by the embedded SQL commands.  But there
   are some functions that can usefully be called directly.  Note that
   this makes your code unportable.
  </para>

  <itemizedlist>
   <listitem>
    <para>
     <function>ECPGdebug(int <replaceable>on</replaceable>, FILE
     *<replaceable>stream</replaceable>)</function> turns on debug
     logging if called with the first argument non-zero. Debug logging
     is done on <replaceable>stream</replaceable>.  The log contains
     all <acronym>SQL</acronym> statements with all the input
     variables inserted, and the results from the
     <productname>PostgreSQL</productname> server. This can be very
     useful when searching for errors in your <acronym>SQL</acronym>
     statements.
    </para>
    <note>
    <para>
    On Windows, if the <application>ecpg</> libraries and an application are
    compiled with different flags, this function call will crash the 
    application because the internal representation of the 
    <literal>FILE</> pointers differ.  Specifically,
    multithreaded/single-threaded, release/debug, and static/dynamic 
    flags should be the same for the library and all applications using
    that library.
    </para>
    </note>
   </listitem>

   <listitem>
     <para>
       <function>ECPGget_PGconn(const char *<replaceable>connection_name</replaceable>)
       </function> returns the library database connection handle identified by the given name.
       If <replaceable>connection_name</replaceable> is set to <literal>NULL</literal>, the current
       connection handle is returned. If no connection handle can be identified, the function returns 
       <literal>NULL</literal>. The returned connection handle can be used to call any other functions
       from <application>libpq</application>, if necessary.
     </para>
     <note>
     <para>
       It is a bad idea to manipulate database connection handles made from <application>ecpg</application> directly
       with <application>libpq</application> routines.
     </para>
     </note>
   </listitem>

   <listitem>
     <para>
       <function>ECPGtransactionStatus(const char *<replaceable>connection_name</replaceable>)</function>
       returns the current transaction status of the given connection identified by <replaceable>connection_name</replaceable>.
       See <xref linkend="libpq-status"> and libpq's <function>PQtransactionStatus()</function> for details about the returned status codes.
     </para>
   </listitem>

   <listitem>
    <para>
     <function>ECPGstatus(int <replaceable>lineno</replaceable>,
     const char* <replaceable>connection_name</replaceable>)</function>
     returns true if you are connected to a database and false if not.
     <replaceable>connection_name</replaceable> can be <literal>NULL</> 
     if a single connection is being used.
    </para>
   </listitem>
  </itemizedlist>
 </sect1>

 <sect1 id="ecpg-develop">
  <title>Internals</title>

  <para>
   This section explains how <application>ECPG</application> works
   internally. This information can occasionally be useful to help
   users understand how to use <application>ECPG</application>.
  </para>

   <para>
    The first four lines written by <command>ecpg</command> to the
    output are fixed lines.  Two are comments and two are include
    lines necessary to interface to the library.  Then the
    preprocessor reads through the file and writes output.  Normally
    it just echoes everything to the output.
   </para>

   <para>
    When it sees an <command>EXEC SQL</command> statement, it
    intervenes and changes it. The command starts with <command>EXEC
    SQL</command> and ends with <command>;</command>. Everything in
    between is treated as an <acronym>SQL</acronym> statement and
    parsed for variable substitution.
   </para>

   <para>
    Variable substitution occurs when a symbol starts with a colon
    (<literal>:</literal>). The variable with that name is looked up
    among the variables that were previously declared within a
    <literal>EXEC SQL DECLARE</> section.
   </para>

   <para>
    The most important function in the library is
    <function>ECPGdo</function>, which takes care of executing most
    commands. It takes a variable number of arguments. This can easily
    add up to 50 or so arguments, and we hope this will not be a
    problem on any platform.
   </para>

   <para>
    The arguments are:

    <variablelist>
     <varlistentry>
      <term>A line number</term>
      <listitem>
       <para>
        This is the line number of the original line; used in error
        messages only.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term>A string</term>
      <listitem>
       <para>
        This is the <acronym>SQL</acronym> command that is to be issued.
        It is modified by the input variables, i.e., the variables that
        where not known at compile time but are to be entered in the
        command. Where the variables should go the string contains
        <literal>?</literal>.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term>Input variables</term>
      <listitem>
       <para>
        Every input variable causes ten arguments to be created.  (See below.)
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><parameter>ECPGt_EOIT</></term>
      <listitem>
       <para>
        An <type>enum</> telling that there are no more input
        variables.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term>Output variables</term>
      <listitem>
       <para>
        Every output variable causes ten arguments to be created.
        (See below.)  These variables are filled by the function.
       </para>
      </listitem>
     </varlistentry>

      <varlistentry>
       <term><parameter>ECPGt_EORT</></term>
       <listitem>
       <para>
        An <type>enum</> telling that there are no more variables.
       </para>
      </listitem>
     </varlistentry>
    </variablelist>
   </para>

   <para>
    For every variable that is part of the <acronym>SQL</acronym>
    command, the function gets ten arguments:

    <orderedlist>
     <listitem>
      <para>
       The type as a special symbol.
      </para>
     </listitem>

     <listitem>
      <para> 
       A pointer to the value or a pointer to the pointer.
      </para>
     </listitem>

     <listitem>
      <para>
       The size of the variable if it is a <type>char</type> or <type>varchar</type>.
      </para>
     </listitem>

     <listitem>
      <para>
       The number of elements in the array (for array fetches).
      </para>
     </listitem>

     <listitem>
      <para>
       The offset to the next element in the array (for array fetches).
      </para>
     </listitem>

     <listitem>
      <para>
       The type of the indicator variable as a special symbol.
      </para>
     </listitem>

     <listitem>
      <para>
       A pointer to the indicator variable.
      </para>
     </listitem>

     <listitem>
      <para>
       0
      </para>
     </listitem>

     <listitem>
      <para>
       The number of elements in the indicator array (for array fetches).
      </para>
     </listitem>

     <listitem>
      <para>
       The offset to the next element in the indicator array (for
       array fetches).
      </para>
     </listitem>
    </orderedlist>
   </para>

   <para>
    Note that not all SQL commands are treated in this way.  For
    instance, an open cursor statement like:
<programlisting>
EXEC SQL OPEN <replaceable>cursor</replaceable>;
</programlisting>
    is not copied to the output. Instead, the cursor's
    <command>DECLARE</> command is used at the position of the <command>OPEN</> command
    because it indeed opens the cursor.
   </para>

   <para>
    Here is a complete example describing the output of the
    preprocessor of a file <filename>foo.pgc</filename> (details might
    change with each particular version of the preprocessor):
<programlisting>
EXEC SQL BEGIN DECLARE SECTION;
int index;
int result;
EXEC SQL END DECLARE SECTION;
...
EXEC SQL SELECT res INTO :result FROM mytable WHERE index = :index;
</programlisting>
    is translated into:
<programlisting><![CDATA[
/* Processed by ecpg (2.6.0) */
/* These two include files are added by the preprocessor */
#include <ecpgtype.h>;
#include <ecpglib.h>;

/* exec sql begin declare section */

#line 1 "foo.pgc"

 int index;
 int result;
/* exec sql end declare section */
...
ECPGdo(__LINE__, NULL, "SELECT res FROM mytable WHERE index = ?     ",
        ECPGt_int,&(index),1L,1L,sizeof(int),
        ECPGt_NO_INDICATOR, NULL , 0L, 0L, 0L, ECPGt_EOIT,
        ECPGt_int,&(result),1L,1L,sizeof(int),
        ECPGt_NO_INDICATOR, NULL , 0L, 0L, 0L, ECPGt_EORT);
#line 147 "foo.pgc"
]]>
</programlisting>
    (The indentation here is added for readability and not
    something the preprocessor does.)
   </para>
 </sect1>
</chapter>
