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<chapter id="ecpg">
<docinfo>
<authorgroup>
<author>
<firstname>Linus</firstname>
<surname>Tolke</surname>
</author>
<author>
<firstname>Michael</firstname>
<surname>Meskes</surname>
</author>
</authorgroup>
<copyright>
<year>1996-1997</year>
<holder>Linus Tolke</holder>
</copyright>
<copyright>
<year>1998</year>
<holder>Michael Meskes</holder>
</copyright>
<date>Transcribed 1998-02-12</date>
</docinfo>
<title><application>ecpg</application> - Embedded <acronym>SQL</acronym>
in <acronym>C</acronym></title>
<indexterm zone="ecpg"><primary>embedded SQL</primary><secondary>in C</secondary></indexterm>
<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>
<para>
This chapter describes the embedded <acronym>SQL</acronym> package
for <productname>PostgreSQL</productname>. It works with
<acronym>C</acronym> and <acronym>C++</acronym>. It was written by
Linus Tolke (<email>linus@epact.se</email>) and Michael Meskes
(<email>meskes@postgresql.org</email>).
</para>
<para>
Admittedly, 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>
This describes the embedded <acronym>SQL</acronym> package for
<productname>PostgreSQL</productname>. It works with
<acronym>C</acronym> and <acronym>C++</acronym>. It was written by
Linus Tolke (<email>linus@epact.se</email>) and Michael Meskes
(<email>meskes@debian.org</email>). The package is installed with the
<productname>PostgreSQL</> distribution, and carries a similar license.
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 to the embedded SQL preprocessor, which converts it
to an ordinary C program, and afterwards it can be processed by a C
compilation tool chain.
</para>
<sect1 id="ecpg-why">
<title>Why Embedded <acronym>SQL</acronym>?</title>
<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. Secondly, embedded
SQL in C is defined in the SQL standard and supported by many other
SQL databases. The 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
<acronym>RDBMS</acronym> to <productname>PostgreSQL</productname>
with relative ease.
</para>
<para>
Embedded <acronym>SQL</acronym> has advantages over other methods
for handling <acronym>SQL</acronym> queries. It takes care of
the tedious passing of information to and from variables in your
<acronym>C</acronym> or <acronym>C++</acronym> program. Many
<acronym>RDBMS</acronym> packages support this embedded language.
</para>
<para>
As indicated, programs written for the embedded SQL 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 may appear in the
global context or within a function. Embedded SQL statements
follow the case-sensitivity rules of normal SQL code, and not those
of C.
</para>
<para>
There is an ANSI standard describing how the embedded language
should work. <application>ecpg</application> was designed to match
this standard as much as possible. It is possible to port embedded
<acronym>SQL</acronym> programs written for other
<acronym>RDBMS</acronym> to <productname>PostgreSQL</productname>.
</para>
</sect1>
<para>
The following sections explain all the embedded SQL statements.
</para>
</sect1>
<sect1 id="ecpg-concept">
<title>The Concept</title>
<sect1 id="ecpg-connect">
<title>Connecting to the Database Server</title>
<para>
You write your program in <acronym>C/C++</acronym> with special
<acronym>SQL</acronym> constructs. When declaring variables to be
used in <acronym>SQL</acronym> statements, you need to put them in a
special <command>declare</> section. You use a special syntax for the
<acronym>SQL</acronym> queries.
</para>
<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>
<literal><replaceable>character variable</replaceable></literal>
</simpara>
</listitem>
<listitem>
<simpara>
<literal><replaceable>character string</replaceable></literal>
</simpara>
</listitem>
<listitem>
<simpara>
<literal>DEFAULT</literal>
</simpara>
</listitem>
</itemizedlist>
</para>
<para>
Before compiling you run the file through the embedded
<acronym>SQL</acronym> <acronym>C</acronym> preprocessor and it
converts the <acronym>SQL</acronym> statements you used to function
calls with the variables used as arguments. Both query input and
result output variables are passed.
</para>
<para>
There are also different ways to specify the user name:
<itemizedlist>
<listitem>
<simpara>
<literal><replaceable>userid</replaceable></literal>
</simpara>
</listitem>
<listitem>
<simpara>
<literal><replaceable>userid</replaceable>/<replaceable>password</replaceable></literal>
</simpara>
</listitem>
<listitem>
<simpara>
<literal><replaceable>userid</replaceable> IDENTIFIED BY <replaceable>password</replaceable></literal>
</simpara>
</listitem>
<listitem>
<simpara>
<literal><replaceable>userid</replaceable> USING <replaceable>password</replaceable></literal>
</simpara>
</listitem>
</itemizedlist>
The <replaceable>userid</replaceable> and
<replaceable>password</replaceable> may be a constant text, a
character variable, or a character string.
</para>
<para>
After compiling, you must link with a special library that contains
needed functions. These functions fetch information from the
arguments, perform the <acronym>SQL</acronym> query using the
<filename>libpq</filename> interface, and put the result in the
arguments specified for output.
</para>
</sect1>
<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.
</para>
</sect1>
<sect1 id="ecpg-use">
<title>How To Use <application>ecpg</application></title>
<sect1 id="ecpg-disconnect">
<title>Closing a Connection</title>
<para>
This section describes how to use <application>ecpg</application>.
</para>
<para>
To close a connection, use the following statement:
<programlisting>
EXEC SQL DISCONNECT [<replaceable>connection</replaceable>];
</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>
</para>
</sect1>
<sect2>
<title>Preprocessor</title>
<sect1 id="ecpg-commands">
<title>Running SQL Commands</title>
<para>
The preprocessor is called <application>ecpg</application>. After
installation it resides in the <productname>PostgreSQL</productname>
<filename>bin/</filename> directory.
</para>
</sect2>
<sect2>
<title>Library</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>
The <application>ecpg</application> library is called
<filename>libecpg.a</filename> or <filename>libecpg.so</filename>.
Additionally, the library uses the <filename>libpq</filename>
library for communication to the
<productname>PostgreSQL</productname> server. You will have to link
your program using <parameter>-lecpg -lpq</parameter>.
</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>
The library has some methods that are <quote>hidden</quote> but may prove
useful.
<para>
Inserting rows:
<programlisting>
EXEC SQL INSERT INTO foo (number, ascii) VALUES (9999, 'doodad');
EXEC SQL COMMIT;
</programlisting>
</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>. Most
<acronym>SQL</acronym> statement log their arguments and results.
</para>
<para>
Deleting rows:
<programlisting>
EXEC SQL DELETE FROM foo WHERE number = 9999;
EXEC SQL COMMIT;
</programlisting>
</para>
<para>
The most important function , <function>ECPGdo</function>, logs
all <acronym>SQL</acronym> statements with both the expanded
string, i.e. the string with all the input variables inserted,
and the result from the <productname>PostgreSQL</productname>
server. This can be very useful when searching for errors in
your <acronym>SQL</acronym> statements.
</para>
</listitem>
<para>
Singleton Select:
<programlisting>
EXEC SQL SELECT foo INTO :FooBar FROM table1 WHERE ascii = 'doodad';
</programlisting>
</para>
<listitem>
<para>
<function>ECPGstatus()</function>
This method returns TRUE if we are connected to a database and FALSE if not.
</para>
</listitem>
</itemizedlist>
</para>
</sect2>
<para>
Select using Cursors:
<programlisting>
EXEC SQL DECLARE foo_bar CURSOR FOR
SELECT number, ascii FROM foo
ORDER BY ascii;
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>
<sect2>
<title>Error handling</title>
<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 the next
section.
</para>
<para>
To detect errors from the <productname>PostgreSQL</productname>
server, include a line like:
<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 (as known from
other interfaces) 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
query 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-variables">
<title>Passing Data</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 a specially marked section, so the embedded
SQL preprocessor is made aware of them.
</para>
<para>
This section starts with
<programlisting>
exec sql include sqlca;
EXEC SQL BEGIN DECLARE SECTION;
</programlisting>
in the include section of your file. This will define a <type>struct</> and
a variable with the name <varname>sqlca</varname> as follows:
and ends with
<programlisting>
struct sqlca
{
char sqlcaid[8];
long sqlabc;
long sqlcode;
struct
{
int sqlerrml;
char sqlerrmc[70];
} sqlerrm;
char sqlerrp[8];
long sqlerrd[6];
/* 0: empty */
/* 1: OID of processed tuple if applicable */
/* 2: number of rows processed in an INSERT, UPDATE */
/* or DELETE statement */
/* 3: empty */
/* 4: empty */
/* 5: empty */
char sqlwarn[8];
/* 0: set to 'W' if at least one other is 'W' */
/* 1: if 'W' at least one character string */
/* value was truncated when it was */
/* stored into a host variable. */
/* 2: empty */
/* 3: empty */
/* 4: empty */
/* 5: empty */
/* 6: empty */
/* 7: empty */
char sqlext[8];
} sqlca;
EXEC SQL END DECLARE SECTION;
</programlisting>
</para>
Between those lines, there must be normal C variable declarations, such as
<programlisting>
int x;
char foo[16], bar[16];
</programlisting>
</para>
<para>
If an no error occurred in the last <acronym>SQL</acronym> statement.
<parameter>sqlca.sqlcode</parameter> will be 0 (<symbol>ECPG_NO_ERROR</>). If
<parameter>sqlca.sqlcode</parameter> is less that zero, this is a
serious error, like the database definition does not match the
query. If it is greater than zero, it is a normal error like the
table did not contain the requested row.
</para>
<para>
The declarations are also echoed to the output file as a normal C
variables, so there's no need to declare them again. Variables
that are not intended to be used with SQL commands can be declared
normally outside these special sections.
</para>
<para>
<parameter>sqlca.sqlerrm.sqlerrmc</parameter> will contain a string
that describes the error. The string ends with the line number in
the source file.
</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>
<para>
These are the errors that can occur:
<para>
The special types <type>VARCHAR</type> and <type>VARCHAR2</type>
are 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>
<variablelist>
<varlistentry>
<term><computeroutput>-12, Out of memory in line %d.</computeroutput></term>
<listitem>
<para>
Should not normally occur. This indicates your virtual memory is
exhausted.
</para>
</listitem>
</varlistentry>
<para>
To use a properly declared C variable in an SQL statement, write
<literal>:<replaceable>varname</></literal> where an expression is
expected. See the previous section for some examples.
</para>
</sect1>
<varlistentry>
<term><computeroutput>-200 (ECPG_UNSUPPORTED): Unsupported type %s on line %d.</computeroutput></term>
<listitem>
<para>
Should not normally occur. This 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.
</para>
</listitem>
</varlistentry>
<sect1 id="ecpg-errors">
<title>Error Handling</title>
<varlistentry>
<term><computeroutput>-201 (ECPG_TOO_MANY_ARGUMENTS): Too many arguments line %d.</computeroutput></term>
<listitem>
<para>
This means that <productname>PostgreSQL</productname> has
returned more arguments than we have matching variables.
Perhaps you have forgotten a couple of the host variables in
the <command>INTO :var1,:var2</command>-list.
</para>
</listitem>
</varlistentry>
<para>
The embedded SQL interface provides a simplistic and a complex way
to handle exceptional conditions in a program. The first method
causes a message to printed automatically when a certain condition
occurs. For example:
<programlisting>
EXEC SQL WHENEVER sqlerror sqlprint;
</programlisting>
or
<programlisting>
EXEC SQL WHENEVER not found sqlprint;
</programlisting>
This error handling remains enabled throughout the entire program.
</para>
<varlistentry>
<term><computeroutput>-202 (ECPG_TOO_FEW_ARGUMENTS): Too few arguments line %d.</computeroutput></term>
<listitem>
<para>
This means that <productname>PostgreSQL</productname> has
returned fewer arguments than we have host variables. Perhaps
you have too many host variables in the <command>INTO
:var1,:var2</command>-list.
</para>
</listitem>
</varlistentry>
<note>
<para>
This is <emphasis>not</emphasis> an exhaustive example of usage
for the <command>EXEC SQL WHENEVER</command> statement. Further
examples of usage may be found in SQL manuals (e.g.,
<citetitle>The LAN TIMES Guide to SQL</> by Groff and Weinberg).
</para>
</note>
<varlistentry>
<term><computeroutput>-203 (ECPG_TOO_MANY_MATCHES): Too many matches line %d.</computeroutput></term>
<listitem>
<para>
This means the query has returned several rows but the
variables specified are not arrays. The
<command>SELECT</command> command was not unique.
</para>
</listitem>
</varlistentry>
<para>
For a more powerful error handling, the embedded SQL interface
provides a <type>struct</> and a variable with the name
<varname>sqlca</varname> as follows:
<programlisting>
struct sqlca
{
char sqlcaid[8];
long sqlabc;
long sqlcode;
struct
{
int sqlerrml;
char sqlerrmc[70];
} sqlerrm;
char sqlerrp[8];
long sqlerrd[6];
/* 0: empty */
/* 1: OID of processed tuple if applicable */
/* 2: number of rows processed in an INSERT, UPDATE */
/* or DELETE statement */
/* 3: empty */
/* 4: empty */
/* 5: empty */
char sqlwarn[8];
/* 0: set to 'W' if at least one other is 'W' */
/* 1: if 'W' at least one character string */
/* value was truncated when it was */
/* stored into a host variable. */
/* 2: empty */
/* 3: empty */
/* 4: empty */
/* 5: empty */
/* 6: empty */
/* 7: empty */
char sqlext[8];
} sqlca;
</programlisting>
(Many of the empty fields may be used in a future release.)
</para>
<varlistentry>
<term><computeroutput>-204 (ECPG_INT_FORMAT): Not correctly formatted int type: %s line %d.</computeroutput></term>
<listitem>
<para>
This means the host variable is of type <type>int</type> and
the field in the <productname>PostgreSQL</productname> database
is of another type and contains a value that cannot be
interpreted as an <type>int</type>. The library uses
<function>strtol()</function> for this conversion.
</para>
</listitem>
</varlistentry>
<para>
If no error occurred in the last <acronym>SQL</acronym> statement,
<literal>sqlca.sqlcode</literal> will be 0
(<symbol>ECPG_NO_ERROR</>). If <literal>sqlca.sqlcode</literal> is
less that zero, this is a serious error, like the database
definition does not match the query. If it is greater than zero, it
is a normal error like the table did not contain the requested row.
</para>
<varlistentry>
<term><computeroutput>-205 (ECPG_UINT_FORMAT): Not correctly formatted unsigned type: %s line %d.</computeroutput></term>
<listitem>
<para>
This means the host variable is of type <type>unsigned
int</type> and the field in the
<productname>PostgreSQL</productname> database is of another type
and contains a value that cannot be interpreted as an
<type>unsigned int</type>. The library uses
<function>strtoul()</function> for this conversion.
</para>
</listitem>
</varlistentry>
<para>
<literal>sqlca.sqlerrm.sqlerrmc</literal> will contain a string
that describes the error. The string ends with the line number in
the source file.
</para>
<varlistentry>
<term><computeroutput>-206 (ECPG_FLOAT_FORMAT): Not correctly formatted floating-point type: %s line %d.</computeroutput></term>
<listitem>
<para>
This means the host variable is of type <type>float</type> and
the field in the <productname>PostgreSQL</productname> 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.
</para>
</listitem>
</varlistentry>
<para>
These are the errors that can occur:
<variablelist>
<varlistentry>
<term><computeroutput>-12, Out of memory in line %d.</computeroutput></term>
<listitem>
<para>
Should not normally occur. This indicates your virtual memory
is exhausted.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><computeroutput>-200 (ECPG_UNSUPPORTED): Unsupported type %s on line %d.</computeroutput></term>
<listitem>
<para>
Should not normally occur. This 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.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><computeroutput>-201 (ECPG_TOO_MANY_ARGUMENTS): Too many arguments line %d.</computeroutput></term>
<listitem>
<para>
This means that the server has returned more arguments than we
have matching variables. Perhaps you have forgotten a couple
of the host variables in the <command>INTO
:var1,:var2</command> list.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><computeroutput>-202 (ECPG_TOO_FEW_ARGUMENTS): Too few arguments line %d.</computeroutput></term>
<listitem>
<para>
This means that the server has returned fewer arguments than we
have host variables. Perhaps you have too many host variables
in the <command>INTO :var1,:var2</command> list. </para>
</listitem>
</varlistentry>
<varlistentry>
<term><computeroutput>-203 (ECPG_TOO_MANY_MATCHES): Too many matches line %d.</computeroutput></term>
<listitem>
<para>
This means the query has returned several rows but the
variables specified are not arrays. The
<command>SELECT</command> command was not unique.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><computeroutput>-204 (ECPG_INT_FORMAT): Not correctly formatted int type: %s line %d.</computeroutput></term>
<listitem>
<para>
This means the host variable is of type <type>int</type> and
the field in the <productname>PostgreSQL</productname> database
is of another type and contains a value that cannot be
interpreted as an <type>int</type>. The library uses
<function>strtol()</function> for this conversion.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><computeroutput>-205 (ECPG_UINT_FORMAT): Not correctly formatted unsigned type: %s line %d.</computeroutput></term>
<listitem>
<para>
This means the host variable is of type <type>unsigned
int</type> and the field in the
<productname>PostgreSQL</productname> database is of another
type and contains a value that cannot be interpreted as an
<type>unsigned int</type>. The library uses
<function>strtoul()</function> for this conversion.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><computeroutput>-206 (ECPG_FLOAT_FORMAT): Not correctly formatted floating-point type: %s line %d.</computeroutput></term>
<listitem>
<para>
This means the host variable is of type <type>float</type> and
the field in the <productname>PostgreSQL</productname> 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.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><computeroutput>-207 (ECPG_CONVERT_BOOL): Unable to convert %s to bool on line %d.</computeroutput></term>
<listitem>
<para>
This means the host variable is of type <type>bool</type> and
the field in the <productname>PostgreSQL</productname> database
is neither <literal>'t'</> nor <literal>'f'</>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><computeroutput>-208 (ECPG_EMPTY): Empty query line %d.</computeroutput></term>
<listitem>
<para>
The query was empty. (This cannot normally happen in an
embedded SQL program, so it may point to an internal error.)
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><computeroutput>-209 (ECPG_MISSING_INDICATOR): NULL value without indicator in line %d.</computeroutput></term>
<listitem>
<para>
A null value was returned and no null indicator variable was
supplied.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><computeroutput>-210 (ECPG_NO_ARRAY): Variable is not an array in line %d.</computeroutput></term>
<listitem>
<para>
An ordinary variable was used in a place that requires an
array.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><computeroutput>-211 (ECPG_DATA_NOT_ARRAY): Data read from backend is not an array in line %d.</computeroutput></term>
<listitem>
<para>
The database returned an ordinary variable in a place that
requires array value.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><computeroutput>-220 (ECPG_NO_CONN): No such connection %s in line %d.</computeroutput></term>
<listitem>
<para>
The program tried to access a connection that does not exist.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><computeroutput>-221 (ECPG_NOT_CONN): Not connected in line %d.</computeroutput></term>
<listitem>
<para>
The program tried to access a connection that does exist but is
not open.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><computeroutput>-230 (ECPG_INVALID_STMT): Invalid statement name %s in line %d.</computeroutput></term>
<listitem>
<para>
The statement you are trying to use has not been prepared.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><computeroutput>-240 (ECPG_UNKNOWN_DESCRIPTOR): Descriptor %s not found in line %d.</computeroutput></term>
<listitem>
<para>
The descriptor specified was not found. The statement you are
trying to use has not been prepared.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><computeroutput>-241 (ECPG_INVALID_DESCRIPTOR_INDEX): Descriptor index out of range in line %d.</computeroutput></term>
<listitem>
<para>
The descriptor index specified was out of range.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><computeroutput>-242 (ECPG_UNKNOWN_DESCRIPTOR_ITEM): Descriptor %s not found in line %d.</computeroutput></term>
<listitem>
<para>
The descriptor specified was not found. The statement you are trying to use has not been prepared.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><computeroutput>-243 (ECPG_VAR_NOT_NUMERIC): Variable is not a numeric type in line %d.</computeroutput></term>
<listitem>
<para>
The database returned a numeric value and the variable was not
numeric.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><computeroutput>-244 (ECPG_VAR_NOT_CHAR): Variable is not a character type in line %d.</computeroutput></term>
<listitem>
<para>
The database returned a non-numeric value and the variable was
numeric.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><computeroutput>-400 (ECPG_PGSQL): Postgres error: %s line %d.</computeroutput></term>
<listitem>
<para>
Some <productname>PostgreSQL</productname> error. The message
contains the error message from the
<productname>PostgreSQL</productname> backend.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><computeroutput>-401 (ECPG_TRANS): Error in transaction processing line %d.</computeroutput></term>
<listitem>
<para>
<productname>PostgreSQL</productname> signaled that we cannot
start, commit, or rollback the transaction.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><computeroutput>-402 (ECPG_CONNECT): Could not connect to database %s in line %d.</computeroutput></term>
<listitem>
<para>
The connect to the database did not work.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><computeroutput>100 (ECPG_NOT_FOUND): Data not found line %d.</computeroutput></term>
<listitem>
<para>
This is a <quote>normal</quote> error that tells you that what
you are querying cannot be found or you are at the end of the
cursor.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</sect1>
<varlistentry>
<term><computeroutput>-207 (ECPG_CONVERT_BOOL): Unable to convert %s to bool on line %d.</computeroutput></term>
<listitem>
<para>
This means the host variable is of type <type>bool</type> and
the field in the <productname>PostgreSQL</productname> database
is neither <literal>'t'</> nor <literal>'f'</>.
</para>
</listitem>
</varlistentry>
<sect1 id="ecpg-include">
<title>Including Files</title>
<varlistentry>
<term><computeroutput>-208 (ECPG_EMPTY): Empty query line %d.</computeroutput></term>
<listitem>
<para>
<productname>PostgreSQL</productname> returned <symbol>PGRES_EMPTY_QUERY</symbol>, probably
because the query indeed was empty.
</para>
</listitem>
</varlistentry>
<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>
<varlistentry>
<term><computeroutput>-209 (ECPG_MISSING_INDICATOR): NULL value without indicator in line %d.</computeroutput></term>
<listitem>
<para>
<productname>PostgreSQL</productname> returned <symbol>ECPG_MISSING_INDICATOR</symbol>
because a NULL was returned and no NULL indicator variable was supplied.
</para>
</listitem>
</varlistentry>
<para>
Note that this is <emphasis>not</emphasis> the same as
<programlisting>
#include &lt;<replaceable>filename</replaceable>.h&gt;
</programlisting>
because the 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>
<varlistentry>
<term><computeroutput>-210 (ECPG_NO_ARRAY): Variable is not an array in line %d.</computeroutput></term>
<listitem>
<para>
<productname>PostgreSQL</productname> returned <symbol>ECPG_NO_ARRAY</symbol>
because an ordinary variable was used in a place that requires
an array.
</para>
</listitem>
</varlistentry>
<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>
</sect1>
<varlistentry>
<term><computeroutput>-211 (ECPG_DATA_NOT_ARRAY): Data read from backend is not an array in line %d.</computeroutput></term>
<listitem>
<para>
<productname>PostgreSQL</productname> returned <symbol>ECPG_DATA_NOT_ARRAY</symbol>
because the database returned an ordinary variable in a place
that requires array value.
</para>
</listitem>
</varlistentry>
<sect1 id="ecpg-process">
<title>Processing Embedded SQL Programs</title>
<varlistentry>
<term><computeroutput>-220 (ECPG_NO_CONN): No such connection %s in line %d.</computeroutput></term>
<listitem>
<para>
The program tried to access a connection that does not exist.
</para>
</listitem>
</varlistentry>
<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> query using
the <application>libpq</application> interface, and put the result
in the arguments specified for output.
</para>
<varlistentry>
<term><computeroutput>-221 (ECPG_NOT_CONN): Not connected in line %d.</computeroutput></term>
<listitem>
<para>
The program tried to access a connection that does exist but is
not open.
</para>
</listitem>
</varlistentry>
<para>
The preprocessor program is called <filename>ecpg</filename> and is
included in a normal 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>
<varlistentry>
<term><computeroutput>-230 (ECPG_INVALID_STMT): Invalid statement name %s in line %d.</computeroutput></term>
<listitem>
<para>
The statement you are trying to use has not been prepared.
</para>
</listitem>
</varlistentry>
<para>
The preprocessed file can be compiled normally, for example
<programlisting>
cc -c prog1.c
</programlisting>
The generated C source files include headers files from the
PostgreSQL installation, so if you installed 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>
<varlistentry>
<term><computeroutput>-240 (ECPG_UNKNOWN_DESCRIPTOR): Descriptor %s not found in line %d.</computeroutput></term>
<listitem>
<para>
The descriptor specified was not found. The statement you are trying to use has not been prepared.
</para>
</listitem>
</varlistentry>
<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>
<varlistentry>
<term><computeroutput>-241 (ECPG_INVALID_DESCRIPTOR_INDEX): Descriptor index out of range in line %d.</computeroutput></term>
<listitem>
<para>
The descriptor index specified was out of range.
</para>
</listitem>
</varlistentry>
<para>
If you manage the build process of a larger project using
<application>make</application>, it may be convenient to include
the following implicit rule to your makefiles:
<programlisting>
ECPG = ecpg
<varlistentry>
<term><computeroutput>-242 (ECPG_UNKNOWN_DESCRIPTOR_ITEM): Descriptor %s not found in line %d.</computeroutput></term>
<listitem>
<para>
The descriptor specified was not found. The statement you are trying to use has not been prepared.
</para>
</listitem>
</varlistentry>
%.c: %.pgc
$(ECPG) $<
</programlisting>
</para>
<varlistentry>
<term><computeroutput>-243 (ECPG_VAR_NOT_NUMERIC): Variable is not a numeric type in line %d.</computeroutput></term>
<listitem>
<para>
The database returned a numeric value and the variable was not
numeric.
</para>
</listitem>
</varlistentry>
<para>
The complete syntax of the <command>ecpg</command> command is
detailed in &cite-reference;.
</para>
</sect1>
<varlistentry>
<term><computeroutput>-244 (ECPG_VAR_NOT_CHAR): Variable is not a character type in line %d.</computeroutput></term>
<listitem>
<para>
The database returned a non-numeric value and the variable was
numeric.
</para>
</listitem>
</varlistentry>
<sect1 id="ecpg-library">
<title>Library Functions</title>
<varlistentry>
<term><computeroutput>-400 (ECPG_PGSQL): Postgres error: %s line %d.</computeroutput></term>
<listitem>
<para>
Some <productname>PostgreSQL</productname> error.
The message contains the error message from the
<productname>PostgreSQL</productname> backend.
</para>
</listitem>
</varlistentry>
<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>
<varlistentry>
<term><computeroutput>-401 (ECPG_TRANS): Error in transaction processing line %d.</computeroutput></term>
<listitem>
<para>
<productname>PostgreSQL</productname> signaled that we cannot start,
commit or rollback the transaction.
</para>
</listitem>
</varlistentry>
<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>. Most
<acronym>SQL</acronym> statement log their arguments and results.
</para>
<varlistentry>
<term><computeroutput>-402 (ECPG_CONNECT): Could not connect to database %s in line %d.</computeroutput></term>
<listitem>
<para>
The connect to the database did not work.
</para>
</listitem>
</varlistentry>
<para>
The most important function, <function>ECPGdo</function>, logs
all <acronym>SQL</acronym> statements with both the expanded
string, i.e. the string with all the input variables inserted,
and the result from the <productname>PostgreSQL</productname>
server. This can be very useful when searching for errors in your
<acronym>SQL</acronym> statements.
</para>
</listitem>
<varlistentry>
<term><computeroutput>100 (ECPG_NOT_FOUND): Data not found line %d.</computeroutput></term>
<listitem>
<para>
This is a <quote>normal</quote> error that tells you that what you are querying cannot
be found or you are at the end of the cursor.
</para>
</listitem>
</varlistentry>
</variablelist>
<listitem>
<para>
<function>ECPGstatus()</function> This method returns true if we
are connected to a database and false if not.
</para>
</sect2>
</sect1>
</listitem>
</itemizedlist>
</sect1>
<sect1 id="ecpg-limitations">
<title>Limitations</title>
<sect1 id="ecpg-porting">
<title>Porting From Other <acronym>RDBMS</acronym> Packages</title>
<para>
What will never be included and why it cannot be done:
<para>
The design of <application>ecpg</application> follows the SQL
standard. Porting from a standard RDBMS should not be a problem.
Unfortunately there is no such thing as a standard RDBMS. Therefore
<application>ecpg</application> tries to understand syntax
extensions as long as they do not create conflicts with the
standard.
</para>
<variablelist>
<varlistentry>
<term>Oracle's single tasking</term>
<listitem>
<para>
Oracle version 7.0 on <systemitem class="osname">AIX</> 3 uses OS-supported locks in shared
memory that allow an application designer to link an application
in a <quote>single tasking</quote> way. Instead of starting one client
process per application process, both the database part and the
application part run in the same process. In later versions of
Oracle this is no longer supported.
</para>
<para>
The following list shows all the known incompatibilities. If you
find one not listed please notify the developers. Note, however,
that we list only incompatibilities from a preprocessor of another
RDBMS to <application>ecpg</application> and not
<application>ecpg</application> features that these RDBMS do not
support.
</para>
<para>
This would require a total redesign of the
<productname>PostgreSQL</productname> access model and the
performance gain does not justify the effort.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</sect1>
<variablelist>
<varlistentry>
<term>Syntax of <command>FETCH</command></term>
<indexterm><primary>FETCH</><secondary>embedded SQL</></indexterm>
<listitem>
<para>
The standard syntax for <command>FETCH</command> is:
<synopsis>
FETCH <optional><replaceable>direction</></> <optional><replaceable>amount</></> IN|FROM <replaceable>cursor</replaceable>
</synopsis>
<indexterm><primary>Oracle</></>
<application>Oracle</application>, however, does not use the
keywords <literal>IN</literal> or <literal>FROM</literal>. This
feature cannot be added since it would create parsing conflicts.
</para>
</listitem>
</varlistentry>
</variablelist>
</sect1>
<sect1 id="ecpg-develop">
<title>For the Developer</title>
<para>
This section explain how <application>ecpg</application> works
internally. This information can occasionally be useful to help
users understand how to use <application>ecpg</application>.
</para>
<sect1 id="ecpg-porting">
<title>Porting From Other <acronym>RDBMS</acronym> Packages</title>
<sect2>
<title>The Preprocessor</title>
<para>
The design of <application>ecpg</application> follows the SQL
standard. Porting from a standard RDBMS should not be a problem.
Unfortunately there is no such thing as a standard RDBMS. Therefore
<application>ecpg</application> tries to understand syntax
extensions as long as they do not create conflicts with the
standard.
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>
The following list shows all the known incompatibilities. If you
find one not listed please notify the developers. Note, however, that
we list only incompatibilities from a precompiler of another RDBMS
to <application>ecpg</application> and not
<application>ecpg</application> features that these RDBMS do not
support.
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>
<variablelist>
<varlistentry>
<term>Syntax of FETCH</term>
<indexterm><primary>FETCH</><secondary>embedded SQL</></indexterm>
<listitem>
<para>
The standard syntax for FETCH is:
</para>
<para>
FETCH [direction] [amount] IN|FROM <replaceable>cursor</replaceable>.
</para>
<para>
<indexterm><primary>Oracle</></>
<application>Oracle</application>, however, does not use the keywords IN
or FROM. This feature cannot be added since it would create parsing
conflicts.
</para>
</listitem>
</varlistentry>
</variablelist>
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. Depending on whether the
variable is being use for input or output, a pointer to the
variable is output to allow access by the function.
</para>
</sect1>
<sect1 id="ecpg-develop">
<title>For the Developer</title>
<para>
This section explain how <application>ecpg</application>
works internally. It contains valuable information to help users
understand how to use <application>ecpg</application>.
For every variable that is part of the <acronym>SQL</acronym>
query, the function gets other arguments:
<itemizedlist>
<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 value of the indicator variable or a pointer
to the pointer of the indicator variable.
</para>
</listitem>
<listitem>
<para>
0
</para>
</listitem>
<listitem>
<para>
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>
</itemizedlist>
</para>
<sect2>
<title>The Preprocessor</title>
<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.
</para>
<para>
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>EXEC SQL</command>
statement can be one of these:
<variablelist>
<varlistentry>
<term>Declare sections</term>
<listitem>
<para>
<command>Declare</> sections begin with:
<programlisting>
exec sql begin declare section;
</programlisting>
and end with:
<programlisting>
exec sql end declare section;
</programlisting>
In this section only variable declarations are allowed. Every
variable declared within this section is stored in a list
of variables indexed by name together with its corresponding
type.
</para>
<para>
In particular the definition of a structure or union also must
be listed inside a <command>declare</> section. Otherwise
<application>ecpg</application> cannot handle these types since
it does not know the definition.
</para>
<para>
The declaration is also echoed to the file to make it a normal
C variable.
</para>
<para>
The special types <type>VARCHAR</type> and
<type>VARCHAR2</type> are 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>
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Include statements</term>
<listitem>
<para>
An include statement looks like:
<programlisting>
exec sql include filename;
</programlisting>
Note that this is NOT the same as:
<programlisting>
#include &lt;filename.h&gt;
</programlisting>
</para>
<para>
Instead the file specified is parsed by
<application>ecpg</application> so the contents of the file are
included in the resulting C code. This way you are able to
specify EXEC SQL commands in an include file.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Connect statement</term>
<listitem>
<para>
A connect statement looks like:
<programlisting>
exec sql connect to <replaceable>connection target</replaceable>;
</programlisting>
It creates a connection to the specified database.
</para>
<para>
The <replaceable>connection target</replaceable> can be specified in the
following ways:
<itemizedlist>
<listitem>
<simpara>
<literal>dbname[@server][:port][as <replaceable>connection
name</replaceable>][user <replaceable>user name</replaceable>]</literal>
</simpara>
</listitem>
<listitem>
<simpara>
<literal>tcp:postgresql://server[:port][/dbname][as
<replaceable>connection name</replaceable>][user <replaceable>user name</replaceable>]</literal>
</simpara>
</listitem>
<listitem>
<simpara>
<literal>unix:postgresql://server[:port][/dbname][as
<replaceable>connection name</replaceable>][user <replaceable>user name</replaceable>]</literal>
</simpara>
</listitem>
<listitem>
<simpara>
<literal><replaceable>character variable</replaceable>[as
<replaceable>connection name</replaceable>][user <replaceable>user name</replaceable>]</literal>
</simpara>
</listitem>
<listitem>
<simpara>
<literal><replaceable>character string</replaceable>[as
<replaceable>connection name</replaceable>][<replaceable>user</replaceable>]</literal>
</simpara>
</listitem>
<listitem>
<simpara>
<literal>default</literal>
</simpara>
</listitem>
<listitem>
<simpara>
<literal>user</literal>
</simpara>
</listitem>
</itemizedlist>
</para>
<para>
There are also different ways to specify the user name:
<itemizedlist>
<listitem>
<simpara>
<literal><replaceable>userid</replaceable></literal>
</simpara>
</listitem>
<listitem>
<simpara>
<literal><replaceable>userid</replaceable>/<replaceable>password</replaceable></literal>
</simpara>
</listitem>
<listitem>
<simpara>
<literal><replaceable>userid</replaceable> identified by <replaceable>password</replaceable></literal>
</simpara>
</listitem>
<listitem>
<simpara>
<literal><replaceable>userid</replaceable> using <replaceable>password</replaceable></literal>
</simpara>
</listitem>
</itemizedlist>
</para>
<para>
Finally, the <replaceable>userid</replaceable> and <replaceable>password</replaceable> may be a constant text, a
character variable, or a character string.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Disconnect statements</term>
<listitem>
<para>
A disconnect statement looks like:
<programlisting>
exec sql disconnect [<replaceable>connection target</replaceable>];
</programlisting>
It closes the connection to the specified database.
</para>
<para>
The <replaceable>connection target</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>
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Open cursor statement</term>
<listitem>
<para>
An open cursor statement looks like:
<programlisting>
exec sql open <replaceable>cursor</replaceable>;
</programlisting>
and is not copied to the output. Instead, the cursor's
<command>DECLARE</> command is used because it opens the cursor
as well.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Commit statement</term>
<listitem>
<para>
A commit statement looks like:
<programlisting>
exec sql commit;
</programlisting>
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Rollback statement</term>
<listitem>
<para>
A rollback statement looks like:
<para>
Note that not all SQL commands are treated in this way. For
instance, an open cursor statement like
<programlisting>
exec sql rollback;
EXEC SQL OPEN <replaceable>cursor</replaceable>;
</programlisting>
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Other statements</term>
<listitem>
<para>
Other <acronym>SQL</acronym> statements are used by
starting with <command>exec sql</command> and ending 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
(<command>:</command>). The variable with that name is looked
up among the variables that were previously declared within a
<command>declare</> section. Depending on whether the variable is
being use for input or output, a pointer to the variable is
output to allow access by the function.
</para>
<para>
For every variable that is part of the <acronym>SQL</acronym>
query, the function gets other arguments:
<itemizedlist>
<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 value of the indicator variable or a pointer to the pointer of the indicator variable.
</para>
</listitem>
<listitem>
<para>
0.
</para>
</listitem>
<listitem>
<para>
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>
</itemizedlist>
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</sect2>
<sect2>
<title>A Complete Example</title>
is not copied to the output. Instead, the cursor's
<command>DECLARE</> command is used because it opens the cursor as
well.
</para>
<para>
Here is a complete example describing the output of the preprocessor of a
file <filename>foo.pgc</filename>:
<para>
Here is a complete example describing the output of the
preprocessor of a file <filename>foo.pgc</filename> (details may
change with each particular version of the preprocessor):
<programlisting>
exec sql begin declare section;
EXEC SQL BEGIN DECLARE SECTION;
int index;
int result;
exec sql end declare section;
EXEC SQL END DECLARE SECTION;
...
exec sql select res into :result from mytable where index = :index;
EXEC SQL SELECT res INTO :result FROM mytable WHERE index = :index;
</programlisting>
is translated into:
is translated into:
<programlisting>
/* Processed by ecpg (2.6.0) */
/* These two include files are added by the preprocessor */
......@@ -964,109 +1028,101 @@ exec sql select res into :result from mytable where index = :index;
int result;
/* exec sql end declare section */
...
ECPGdo(__LINE__, NULL, "select res from mytable where index = ? ",
ECPGdo(__LINE__, NULL, "SELECT res FROM mytable WHERE index = ? ",
ECPGt_int,&amp;(index),1L,1L,sizeof(int),
ECPGt_NO_INDICATOR, NULL , 0L, 0L, 0L, ECPGt_EOIT,
ECPGt_int,&amp;(result),1L,1L,sizeof(int),
ECPGt_NO_INDICATOR, NULL , 0L, 0L, 0L, ECPGt_EORT);
#line 147 "foo.pgc"
</programlisting>
(The indentation in this manual is added for readability and not
something the preprocessor does.)
</para>
</sect2>
(The indentation in this manual is added for readability and not
something the preprocessor does.)
</para>
</sect2>
<sect2>
<title>The Library</title>
<sect2>
<title>The Library</title>
<para>
The most important function in the library is
<function>ECPGdo</function>. It takes a variable number of
arguments. Hopefully there are no computers that limit the
number of variables that can be accepted by a <function>varargs()</function> function. This
can easily add up to 50 or so arguments.
</para>
<para>
The most important function in the library is
<function>ECPGdo</function>. It takes a variable number of
arguments. Hopefully there are no computers that limit the number
of variables that can be accepted by a
<function>varargs()</function> function. This can easily add up to
50 or so arguments.
</para>
<para>
The arguments are:
<para>
The arguments are:
<variablelist>
<varlistentry>
<term>A line number</term>
<listitem>
<para>
This is a line number of the original line; used in error messages only.
</para>
</listitem>
</varlistentry>
<variablelist>
<varlistentry>
<term>A line number</term>
<listitem>
<para>
This is a 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> query 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
query. Where the variables should go the string contains
<literal>?</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>A string</term>
<listitem>
<para>
This is the <acronym>SQL</acronym> query 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
query. Where the variables should go the string contains
<literal>?</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Input variables</term>
<listitem>
<para>
As described in the section about the preprocessor, every input variable
gets ten arguments.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Input variables</term>
<listitem>
<para>
As described in the section about the preprocessor, every
input variable gets ten arguments.
</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><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>
As described in the section about the preprocessor, every input variable
gets ten arguments. These variables are filled by the function.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Output variables</term>
<listitem>
<para>
As described in the section about the preprocessor, every
input variable gets ten arguments. 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>
In the default mode, queries are committed only when <command>exec
sql commit</command> is issued. <application>Ecpg</application>
also supports auto-commit of transactions via the
<option>-t</option> command-line option or via the <literal>exec
sql set autocommit to on</literal> statement. In
<literal>autocommit</literal> mode, each query 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>
</sect2>
</sect1>
</chapter>
<para>
An <type>enum</> telling that there are no more variables.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</sect2>
</sect1>
</chapter>
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PostgreSQL documentation
-->
<refentry id="APP-ECPG">
<refmeta>
<refentrytitle id="app-ecpg-title"><application>ecpg</application></refentrytitle>
<refentrytitle><application>ecpg</application></refentrytitle>
<manvolnum>1</manvolnum>
<refmiscinfo>Application</refmiscinfo>
</refmeta>
<refnamediv>
<refname>
<application>ecpg</application>
</refname>
<refpurpose>
embedded SQL C preprocessor
</refpurpose>
<refname><application>ecpg</application></refname>
<refpurpose>embedded SQL C preprocessor</refpurpose>
</refnamediv>
<refsynopsisdiv>
<refsynopsisdivinfo>
<date>1999-07-20</date>
</refsynopsisdivinfo>
<cmdsynopsis>
<command>ecpg</command>
<arg choice="opt">-v</arg>
<arg choice="opt">-t</arg>
<arg choice="opt">-I <replaceable>include-path</replaceable></arg>
<arg choice="opt">-o <replaceable>outfile</replaceable></arg>
<arg choice="opt" rep="repeat"><replaceable>option</replaceable></arg>
<arg choice="plain" rep="repeat"><replaceable>file</replaceable></arg>
</cmdsynopsis>
</refsynopsisdiv>
<refsect1 id="APP-ECPG-description">
<title>Description</title>
<para>
<application>ecpg</application>
is an embedded SQL preprocessor for the C language and the
<productname>PostgreSQL</productname>. It
enables development of C programs with embedded SQL code.
<command>ecpg</command> is the embedded SQL preprocessor for C
programs. It converts C programs with embedded SQL statements to
normal C code by replacing the SQL invocations with special
function calls. The output files can then be processed with any C
compiler tool chain.
</para>
<para>
Linus Tolke (<email>linus@epact.se</email>) was the
original author of <application>ecpg</application> (up to version 0.2).
Michael Meskes (<email>meskes@debian.org</email>)
is the current author and maintainer of <application>ecpg</application>.
Thomas Good (<email>tomg@q8.nrnet.org</email>)
is the author of the last revision of the <application>ecpg</application> man page, on which
this document is based.
<command>ecpg</command> will convert each input file given on the
command line to the corresponding C output file. Input files
preferrably have the extension <filename>.pgc</filename>, in which
case the extension will be replaced by <filename>.c</filename> to
determine the output file name. If the extension of the input file
is not <filename>.pgc</filename>, then the output file name is
computed by appending <literal>.c</literal> to the full file name.
The output file name can also be overridden using the
<option>-o</option> option.
</para>
</refsect1>
<refsect1>
<title>Options</title>
<para>
<application>ecpg</application> accepts the following command
line arguments:
<variablelist>
<varlistentry>
<term>-v</term>
<listitem>
<para>
Print version information.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>-t</term>
<listitem>
<para>
Turn on auto-commit of transactions. In this mode, each query is
automatically committed unless it is inside an explicit
transaction block. In the default mode, queries are committed
only when <command>exec sql commit</command> is issued.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>-I <replaceable class="parameter">include-path</replaceable></term>
<listitem>
<para>
Specify an additional include path.
Defaults are <filename>.</filename> (current directory),
<filename>/usr/local/include</filename>, the
<productname>PostgreSQL</productname> include path which is
defined at compile time (default:
<filename>/usr/local/pgsql/include</filename>), and
<filename>/usr/include</filename>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>-o <replaceable>outfile</replaceable></term>
<listitem>
<para>
Specifies that <application>ecpg</application> should write all its output to <replaceable>outfile</replaceable>.
If no such option is given the output is written to
<filename><replaceable>name</replaceable>.c</filename>,
assuming the input file was
named <filename><replaceable>name</replaceable>.pgc</filename>.
If the input file does have the expected
<literal>.pgc</literal> suffix, then the output file will have
<literal>.pgc</literal> appended to the input file name.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="parameter">file</replaceable></term>
<listitem>
<para>
The files to be processed.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
<para>
This reference page does not describe the embedded SQL language.
See &cite-programmer; for that.
</para>
</refsect1>
<refsect1>
<title>Exit Status</title>
<title>Options</title>
<para>
<application>ecpg</application> returns 0 to the shell on
successful completion, non-zero for errors.
<command>ecpg</command> accepts the following command-line
arguments:
<variablelist>
<varlistentry>
<term><option>-c</option></term>
<listitem>
<para>
Automatically generate C code from SQL code. Currently, this
works for <literal>EXEC SQL TYPE</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-D <replaceable>symbol</replaceable></option></term>
<listitem>
<para>
Define a C preprocessor symbol.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-I <replaceable class="parameter">directory</replaceable></option></term>
<listitem>
<para>
Specify an additional include path, used to find files included
via <literal>EXEC SQL INCLUDE</literal>. Defaults are
<filename>.</filename> (current directory),
<filename>/usr/local/include</filename>, the
<productname>PostgreSQL</productname> include directory which
is defined at compile time (default:
<filename>/usr/local/pgsql/include</filename>), and
<filename>/usr/include</filename>, in that order.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-o <replaceable>filename</replaceable></option></term>
<listitem>
<para>
Specifies that <application>ecpg</application> should write all
its output to the given <replaceable>filename</replaceable>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-t</option></term>
<listitem>
<para>
Turn on autocommit of transactions. In this mode, each query is
automatically committed unless it is inside an explicit
transaction block. In the default mode, queries are committed
only when <command>EXEC SQL COMMIT</command> is issued.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-v</option></term>
<listitem>
<para>
Print additional information including the version and the
include path.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>---help</option></term>
<listitem>
<para>
Show a brief summary of the command usage, then exit.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--version</option></term>
<listitem>
<para>
Output version information, then exit.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</refsect1>
<refsect1>
<title>Usage</title>
<refsect2 id="APP-ECPG-preprocessing">
<title>Preprocessing for Compilation</title>
<para>
An embedded SQL source file must be preprocessed before
compilation:
<synopsis>
ecpg [ -d ] [ -o <replaceable>file</replaceable> ] <replaceable>file</replaceable>.pgc
</synopsis>
where the optional <option>-d</option> flag turns on debugging.
The <literal>.pgc</literal> extension is an
arbitrary means of denoting <application>ecpg</application> source.
</para>
<para>
You may want to redirect the preprocessor output to a log file.
</para>
</refsect2>
<title>Notes</title>
<refsect2 id="APP-ECPG-compiling">
<title>Compiling and Linking</title>
<para>
When compiling the preprocessed C code files, the compiler needs to
be able to find the <application>ECPG</> header files in the
PostgreSQL include directory. Therefore, one might have to use the
<option>-I</> option when invoking the compiler (e.g.,
<literal>-I/usr/local/pgsql/include</literal>).
</para>
<para>
Assuming the <productname>PostgreSQL</productname> binaries are in
<filename>/usr/local/pgsql</filename>, you will need to compile
and link your preprocessed source file:
<para>
Programs using C code with embedded SQL have to be linked against
the <filename>libecpg</filename> library, for example using the
flags <literal>-L/usr/local/pgsql/lib -lecpg</literal>.
</para>
<synopsis>
gcc -g -I /usr/local/pgsql/include [ -o <replaceable>file</replaceable> ] <replaceable>file</replaceable>.c -L /usr/local/pgsql/lib -lecpg -lpq
</synopsis>
</para>
</refsect2>
<para>
The value of either of these directories that is appropriate for
the installation can be found out using <xref
linkend="app-pgconfig">.
</para>
</refsect1>
<refsect1 id="APP-ECPG-grammar">
<title>Grammar</title>
<refsect2 id="APP-ECPG-library">
<title>Libraries</title>
<para>
The preprocessor will prepend two directives to the source:
<programlisting>
#include &lt;ecpgtype.h&gt;
#include &lt;ecpglib.h&gt;
</programlisting>
</para>
</refsect2>
<refsect2 id="APP-ecpg-declaration">
<title>Variable Declaration</title>
<para>
Variables declared within <application>ecpg</application> source code must be prepended with:
<programlisting>
EXEC SQL BEGIN DECLARE SECTION;
</programlisting>
</para>
<para>
Similarly, variable declaration sections must terminate with:
<programlisting>
EXEC SQL END DECLARE SECTION;
</programlisting>
<note>
<para>
Prior to version 2.1.0, each variable had to be declared
on a separate line. As of version 2.1.0 multiple variables may
be declared on a single line:
<programlisting>
char foo[16], bar[16];
</programlisting>
</para>
</note>
</para>
</refsect2>
<refsect2 id="APP-ECPG-errors">
<title>Error Handling</title>
<para>
The SQL communication area is defined with:
<programlisting>
EXEC SQL INCLUDE sqlca;
</programlisting>
</para>
<note>
<para>
The <literal>sqlca</literal> is in lowercase.
While SQL convention may be
followed, i.e., using uppercase to separate embedded SQL
from C statements, <literal>sqlca</literal> (which includes the <filename>sqlca.h</>
header file) <emphasis>must</> be lowercase. This is because the
EXEC SQL prefix indicates that this inclusion will be parsed by
<application>ecpg</application>.
<application>ecpg</application> observes case sensitivity
(<filename>SQLCA.h</> will not be found).
<command>EXEC SQL INCLUDE</command>
can be used to include other header files
as long as case sensitivity is observed.
</para>
</note>
<para>
The <literal>sqlprint</literal> command is used with the <literal>EXEC SQL WHENEVER</literal>
statement to turn on error handling throughout the
program:
<programlisting>
EXEC SQL WHENEVER sqlerror sqlprint;
</programlisting>
and
<programlisting>
EXEC SQL WHENEVER not found sqlprint;
</programlisting>
</para>
<note>
<para>
This is <emphasis>not</emphasis> an exhaustive example of usage for
the <command>EXEC SQL WHENEVER</command> statement.
Further examples of usage may
be found in SQL manuals (e.g., <citetitle>The LAN TIMES Guide to SQL</> by
Groff and Weinberg).
</para>
</note>
</refsect2>
<refsect2 id="APP-ECPG-connecting">
<title>Connecting to the Database Server</title>
<para>
One connects to a database using the following:
<programlisting>
EXEC SQL CONNECT TO <replaceable>dbname</replaceable>;
</programlisting>
where the database name is not quoted. Prior to version 2.1.0, the
database name was required to be inside single quotes.
</para>
<para>
Specifying a server and port name in the connect statement is also
possible. The syntax is:
<synopsis>
<replaceable>dbname</replaceable>[@<replaceable>server</replaceable>][:<replaceable>port</replaceable>]
</synopsis>
or
<synopsis>
&lt;tcp|unix&gt;:postgresql://<replaceable>server</replaceable>[:<replaceable>port</replaceable>][/<replaceable>dbname</replaceable>][?<replaceable>options</replaceable>]
</synopsis>
</para>
</refsect2>
<refsect2 id="APP-ECPG-queries">
<title>Queries</title>
<para>
In general, SQL queries acceptable to other applications such as
<application>psql</application> can be embedded into your C
code. Here are some examples of how to do that.
</para>
<para>
Create Table:
<programlisting>
EXEC SQL CREATE TABLE foo (number int4, ascii char(16));
EXEC SQL CREATE UNIQUE index num1 on foo(number);
EXEC SQL COMMIT;
</programlisting>
</para>
<para>
Insert:
<programlisting>
EXEC SQL INSERT INTO foo (number, ascii) VALUES (9999, 'doodad');
EXEC SQL COMMIT;
</programlisting>
</para>
<para>
Delete:
<programlisting>
EXEC SQL DELETE FROM foo WHERE number = 9999;
EXEC SQL COMMIT;
</programlisting>
</para>
<para>
Singleton 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 FETCH foo_bar INTO :FooBar, DooDad;
...
EXEC SQL CLOSE foo_bar;
EXEC SQL COMMIT;
</programlisting>
</para>
<refsect1>
<title>Examples</title>
<para>
Updates:
<para>
If you have an embedded SQL C source file named
<filename>prog1.pgc</filename>, you can create an executable
program using the following sequence of commands:
<programlisting>
EXEC SQL UPDATE foo
SET ascii = 'foobar'
WHERE number = 9999;
EXEC SQL COMMIT;
ecpg prog1.pgc
cc -I/usr/local/pgsql/include -c prog1.c
cc -o prog1 prog1.o -L/usr/local/pgsql/lib -lecpg
</programlisting>
</para>
</refsect2>
</refsect1>
<refsect1 id="APP-ECPG-notes">
<title>Notes</title>
<para>
The complete structure definition MUST be listed
inside the declare section.
</para>
<para>
See the <filename>TODO</filename> file in the source for some more
missing features.
</para>
</refsect1>
......@@ -399,7 +197,7 @@ EXEC SQL COMMIT;
<para>
<citetitle>PostgreSQL Programmer's Guide</citetitle> for a more
detailed description of the embedded SQL interface.
detailed description of the embedded SQL interface
</para>
</refsect1>
......
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