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$Header: /cvsroot/pgsql/doc/src/sgml/ecpg.sgml,v 1.37 2002/09/21 18:32:52 petere Exp $ $Header: /cvsroot/pgsql/doc/src/sgml/ecpg.sgml,v 1.38 2002/10/21 18:04:05 petere Exp $
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<chapter id="ecpg"> <chapter id="ecpg">
<docinfo> <title><application>ECPG</application> - Embedded <acronym>SQL</acronym> in C</title>
<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> <indexterm zone="ecpg"><primary>embedded SQL</primary><secondary>in C</secondary></indexterm>
<para> <para>
This describes the embedded <acronym>SQL</acronym> package for This chapter describes the embedded <acronym>SQL</acronym> package
<productname>PostgreSQL</productname>. It works with for <productname>PostgreSQL</productname>. It works with
<acronym>C</acronym> and <acronym>C++</acronym>. It was written by <acronym>C</acronym> and <acronym>C++</acronym>. It was written by
Linus Tolke (<email>linus@epact.se</email>) and Michael Meskes Linus Tolke (<email>linus@epact.se</email>) and Michael Meskes
(<email>meskes@debian.org</email>). The package is installed with the (<email>meskes@postgresql.org</email>).
<productname>PostgreSQL</> distribution, and carries a similar license.
</para> </para>
<sect1 id="ecpg-why"> <para>
<title>Why Embedded <acronym>SQL</acronym>?</title> 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>
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>
<para> <para>
Embedded <acronym>SQL</acronym> has advantages over other methods Embedded <acronym>SQL</acronym> has advantages over other methods
for handling <acronym>SQL</acronym> queries. It takes care of for handling <acronym>SQL</acronym> commands from C code. First, it
the tedious passing of information to and from variables in your takes care of the tedious passing of information to and from
<acronym>C</acronym> or <acronym>C++</acronym> program. Many variables in your <acronym>C</acronym> program. Secondly, embedded
<acronym>RDBMS</acronym> packages support this embedded language. 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>
<para> <para>
There is an ANSI standard describing how the embedded language As indicated, programs written for the embedded SQL interface are
should work. <application>ecpg</application> was designed to match normal C programs with special code inserted to perform
this standard as much as possible. It is possible to port embedded database-related actions. This special code always has the form
<acronym>SQL</acronym> programs written for other <programlisting>
<acronym>RDBMS</acronym> to <productname>PostgreSQL</productname>. 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>
The following sections explain all the embedded SQL statements.
</para> </para>
</sect1> </sect1>
<sect1 id="ecpg-concept"> <sect1 id="ecpg-connect">
<title>The Concept</title> <title>Connecting to the Database Server</title>
<para> <para>
You write your program in <acronym>C/C++</acronym> with special One connects to a database using the following statement:
<acronym>SQL</acronym> constructs. When declaring variables to be <programlisting>
used in <acronym>SQL</acronym> statements, you need to put them in a EXEC SQL CONNECT TO <replaceable>target</replaceable> <optional>AS <replaceable>connection-name</replaceable></optional> <optional>USER <replaceable>user-name</replaceable></optional>;
special <command>declare</> section. You use a special syntax for the </programlisting>
<acronym>SQL</acronym> queries. 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>
<para> <para>
Before compiling you run the file through the embedded There are also different ways to specify the user name:
<acronym>SQL</acronym> <acronym>C</acronym> preprocessor and it
converts the <acronym>SQL</acronym> statements you used to function <itemizedlist>
calls with the variables used as arguments. Both query input and <listitem>
result output variables are passed. <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>
<para> <para>
After compiling, you must link with a special library that contains The <replaceable>connection-name</replaceable> is used to handle
needed functions. These functions fetch information from the multiple connections in one program. It can be omitted if a
arguments, perform the <acronym>SQL</acronym> query using the program uses only one connection.
<filename>libpq</filename> interface, and put the result in the
arguments specified for output.
</para> </para>
</sect1> </sect1>
<sect1 id="ecpg-use"> <sect1 id="ecpg-disconnect">
<title>How To Use <application>ecpg</application></title> <title>Closing a Connection</title>
<para> <para>
This section describes how to use <application>ecpg</application>. 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> </para>
</sect1>
<sect2> <sect1 id="ecpg-commands">
<title>Preprocessor</title> <title>Running SQL Commands</title>
<para> <para>
The preprocessor is called <application>ecpg</application>. After Any SQL command can be run from within an embedded SQL application.
installation it resides in the <productname>PostgreSQL</productname> Below are some examples of how to do that.
<filename>bin/</filename> directory. </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>
</sect2>
<sect2>
<title>Library</title>
<para> <para>
The <application>ecpg</application> library is called Inserting rows:
<filename>libecpg.a</filename> or <filename>libecpg.so</filename>. <programlisting>
Additionally, the library uses the <filename>libpq</filename> EXEC SQL INSERT INTO foo (number, ascii) VALUES (9999, 'doodad');
library for communication to the EXEC SQL COMMIT;
<productname>PostgreSQL</productname> server. You will have to link </programlisting>
your program using <parameter>-lecpg -lpq</parameter>.
</para> </para>
<para> <para>
The library has some methods that are <quote>hidden</quote> but may prove Deleting rows:
useful. <programlisting>
EXEC SQL DELETE FROM foo WHERE number = 9999;
EXEC SQL COMMIT;
</programlisting>
</para>
<itemizedlist>
<listitem>
<para> <para>
<function>ECPGdebug(int <replaceable>on</replaceable>, FILE Singleton Select:
*<replaceable>stream</replaceable>)</function> turns on debug <programlisting>
logging if called with the first argument non-zero. Debug EXEC SQL SELECT foo INTO :FooBar FROM table1 WHERE ascii = 'doodad';
logging is done on <replaceable>stream</replaceable>. Most </programlisting>
<acronym>SQL</acronym> statement log their arguments and results.
</para> </para>
<para> <para>
The most important function , <function>ECPGdo</function>, logs Select using Cursors:
all <acronym>SQL</acronym> statements with both the expanded <programlisting>
string, i.e. the string with all the input variables inserted, EXEC SQL DECLARE foo_bar CURSOR FOR
and the result from the <productname>PostgreSQL</productname> SELECT number, ascii FROM foo
server. This can be very useful when searching for errors in ORDER BY ascii;
your <acronym>SQL</acronym> statements. EXEC SQL FETCH foo_bar INTO :FooBar, DooDad;
...
EXEC SQL CLOSE foo_bar;
EXEC SQL COMMIT;
</programlisting>
</para> </para>
</listitem>
<listitem>
<para> <para>
<function>ECPGstatus()</function> Updates:
This method returns TRUE if we are connected to a database and FALSE if not. <programlisting>
EXEC SQL UPDATE foo
SET ascii = 'foobar'
WHERE number = 9999;
EXEC SQL COMMIT;
</programlisting>
</para> </para>
</listitem>
</itemizedlist> <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>
</sect2>
<sect2> <para>
<title>Error handling</title> 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 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;
char foo[16], bar[16];
</programlisting>
</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>
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>
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>
<para> <para>
To detect errors from the <productname>PostgreSQL</productname> To use a properly declared C variable in an SQL statement, write
server, include a line like: <literal>:<replaceable>varname</></literal> where an expression is
expected. See the previous section for some examples.
</para>
</sect1>
<sect1 id="ecpg-errors">
<title>Error Handling</title>
<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> <programlisting>
exec sql include sqlca; EXEC SQL WHENEVER sqlerror sqlprint;
</programlisting> </programlisting>
in the include section of your file. This will define a <type>struct</> and or
a variable with the name <varname>sqlca</varname> as follows: <programlisting>
EXEC SQL WHENEVER not found sqlprint;
</programlisting>
This error handling remains enabled throughout the entire program.
</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>
<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> <programlisting>
struct sqlca struct sqlca
{ {
...@@ -172,6 +383,7 @@ struct sqlca ...@@ -172,6 +383,7 @@ struct sqlca
char sqlerrmc[70]; char sqlerrmc[70];
} sqlerrm; } sqlerrm;
char sqlerrp[8]; char sqlerrp[8];
long sqlerrd[6]; long sqlerrd[6];
/* 0: empty */ /* 0: empty */
/* 1: OID of processed tuple if applicable */ /* 1: OID of processed tuple if applicable */
...@@ -180,6 +392,7 @@ struct sqlca ...@@ -180,6 +392,7 @@ struct sqlca
/* 3: empty */ /* 3: empty */
/* 4: empty */ /* 4: empty */
/* 5: empty */ /* 5: empty */
char sqlwarn[8]; char sqlwarn[8];
/* 0: set to 'W' if at least one other is 'W' */ /* 0: set to 'W' if at least one other is 'W' */
/* 1: if 'W' at least one character string */ /* 1: if 'W' at least one character string */
...@@ -191,22 +404,24 @@ struct sqlca ...@@ -191,22 +404,24 @@ struct sqlca
/* 5: empty */ /* 5: empty */
/* 6: empty */ /* 6: empty */
/* 7: empty */ /* 7: empty */
char sqlext[8]; char sqlext[8];
} sqlca; } sqlca;
</programlisting> </programlisting>
(Many of the empty fields may be used in a future release.)
</para> </para>
<para> <para>
If an no error occurred in the last <acronym>SQL</acronym> statement. If no error occurred in the last <acronym>SQL</acronym> statement,
<parameter>sqlca.sqlcode</parameter> will be 0 (<symbol>ECPG_NO_ERROR</>). If <literal>sqlca.sqlcode</literal> will be 0
<parameter>sqlca.sqlcode</parameter> is less that zero, this is a (<symbol>ECPG_NO_ERROR</>). If <literal>sqlca.sqlcode</literal> is
serious error, like the database definition does not match the less that zero, this is a serious error, like the database
query. If it is greater than zero, it is a normal error like the definition does not match the query. If it is greater than zero, it
table did not contain the requested row. is a normal error like the table did not contain the requested row.
</para> </para>
<para> <para>
<parameter>sqlca.sqlerrm.sqlerrmc</parameter> will contain a string <literal>sqlca.sqlerrm.sqlerrmc</literal> will contain a string
that describes the error. The string ends with the line number in that describes the error. The string ends with the line number in
the source file. the source file.
</para> </para>
...@@ -219,8 +434,8 @@ struct sqlca ...@@ -219,8 +434,8 @@ struct sqlca
<term><computeroutput>-12, Out of memory in line %d.</computeroutput></term> <term><computeroutput>-12, Out of memory in line %d.</computeroutput></term>
<listitem> <listitem>
<para> <para>
Should not normally occur. This indicates your virtual memory is Should not normally occur. This indicates your virtual memory
exhausted. is exhausted.
</para> </para>
</listitem> </listitem>
</varlistentry> </varlistentry>
...@@ -241,10 +456,10 @@ struct sqlca ...@@ -241,10 +456,10 @@ struct sqlca
<term><computeroutput>-201 (ECPG_TOO_MANY_ARGUMENTS): Too many arguments line %d.</computeroutput></term> <term><computeroutput>-201 (ECPG_TOO_MANY_ARGUMENTS): Too many arguments line %d.</computeroutput></term>
<listitem> <listitem>
<para> <para>
This means that <productname>PostgreSQL</productname> has This means that the server has returned more arguments than we
returned more arguments than we have matching variables. have matching variables. Perhaps you have forgotten a couple
Perhaps you have forgotten a couple of the host variables in of the host variables in the <command>INTO
the <command>INTO :var1,:var2</command>-list. :var1,:var2</command> list.
</para> </para>
</listitem> </listitem>
</varlistentry> </varlistentry>
...@@ -253,11 +468,9 @@ struct sqlca ...@@ -253,11 +468,9 @@ struct sqlca
<term><computeroutput>-202 (ECPG_TOO_FEW_ARGUMENTS): Too few arguments line %d.</computeroutput></term> <term><computeroutput>-202 (ECPG_TOO_FEW_ARGUMENTS): Too few arguments line %d.</computeroutput></term>
<listitem> <listitem>
<para> <para>
This means that <productname>PostgreSQL</productname> has This means that the server has returned fewer arguments than we
returned fewer arguments than we have host variables. Perhaps have host variables. Perhaps you have too many host variables
you have too many host variables in the <command>INTO in the <command>INTO :var1,:var2</command> list. </para>
:var1,:var2</command>-list.
</para>
</listitem> </listitem>
</varlistentry> </varlistentry>
...@@ -291,8 +504,8 @@ struct sqlca ...@@ -291,8 +504,8 @@ struct sqlca
<para> <para>
This means the host variable is of type <type>unsigned This means the host variable is of type <type>unsigned
int</type> and the field in the int</type> and the field in the
<productname>PostgreSQL</productname> database is of another type <productname>PostgreSQL</productname> database is of another
and contains a value that cannot be interpreted as an type and contains a value that cannot be interpreted as an
<type>unsigned int</type>. The library uses <type>unsigned int</type>. The library uses
<function>strtoul()</function> for this conversion. <function>strtoul()</function> for this conversion.
</para> </para>
...@@ -327,8 +540,8 @@ struct sqlca ...@@ -327,8 +540,8 @@ struct sqlca
<term><computeroutput>-208 (ECPG_EMPTY): Empty query line %d.</computeroutput></term> <term><computeroutput>-208 (ECPG_EMPTY): Empty query line %d.</computeroutput></term>
<listitem> <listitem>
<para> <para>
<productname>PostgreSQL</productname> returned <symbol>PGRES_EMPTY_QUERY</symbol>, probably The query was empty. (This cannot normally happen in an
because the query indeed was empty. embedded SQL program, so it may point to an internal error.)
</para> </para>
</listitem> </listitem>
</varlistentry> </varlistentry>
...@@ -337,8 +550,8 @@ struct sqlca ...@@ -337,8 +550,8 @@ struct sqlca
<term><computeroutput>-209 (ECPG_MISSING_INDICATOR): NULL value without indicator in line %d.</computeroutput></term> <term><computeroutput>-209 (ECPG_MISSING_INDICATOR): NULL value without indicator in line %d.</computeroutput></term>
<listitem> <listitem>
<para> <para>
<productname>PostgreSQL</productname> returned <symbol>ECPG_MISSING_INDICATOR</symbol> A null value was returned and no null indicator variable was
because a NULL was returned and no NULL indicator variable was supplied. supplied.
</para> </para>
</listitem> </listitem>
</varlistentry> </varlistentry>
...@@ -347,9 +560,8 @@ struct sqlca ...@@ -347,9 +560,8 @@ struct sqlca
<term><computeroutput>-210 (ECPG_NO_ARRAY): Variable is not an array in line %d.</computeroutput></term> <term><computeroutput>-210 (ECPG_NO_ARRAY): Variable is not an array in line %d.</computeroutput></term>
<listitem> <listitem>
<para> <para>
<productname>PostgreSQL</productname> returned <symbol>ECPG_NO_ARRAY</symbol> An ordinary variable was used in a place that requires an
because an ordinary variable was used in a place that requires array.
an array.
</para> </para>
</listitem> </listitem>
</varlistentry> </varlistentry>
...@@ -358,9 +570,8 @@ struct sqlca ...@@ -358,9 +570,8 @@ struct sqlca
<term><computeroutput>-211 (ECPG_DATA_NOT_ARRAY): Data read from backend is not an array in line %d.</computeroutput></term> <term><computeroutput>-211 (ECPG_DATA_NOT_ARRAY): Data read from backend is not an array in line %d.</computeroutput></term>
<listitem> <listitem>
<para> <para>
<productname>PostgreSQL</productname> returned <symbol>ECPG_DATA_NOT_ARRAY</symbol> The database returned an ordinary variable in a place that
because the database returned an ordinary variable in a place requires array value.
that requires array value.
</para> </para>
</listitem> </listitem>
</varlistentry> </varlistentry>
...@@ -397,7 +608,8 @@ struct sqlca ...@@ -397,7 +608,8 @@ struct sqlca
<term><computeroutput>-240 (ECPG_UNKNOWN_DESCRIPTOR): Descriptor %s not found in line %d.</computeroutput></term> <term><computeroutput>-240 (ECPG_UNKNOWN_DESCRIPTOR): Descriptor %s not found in line %d.</computeroutput></term>
<listitem> <listitem>
<para> <para>
The descriptor specified was not found. The statement you are trying to use has not been prepared. The descriptor specified was not found. The statement you are
trying to use has not been prepared.
</para> </para>
</listitem> </listitem>
</varlistentry> </varlistentry>
...@@ -444,8 +656,8 @@ struct sqlca ...@@ -444,8 +656,8 @@ struct sqlca
<term><computeroutput>-400 (ECPG_PGSQL): Postgres error: %s line %d.</computeroutput></term> <term><computeroutput>-400 (ECPG_PGSQL): Postgres error: %s line %d.</computeroutput></term>
<listitem> <listitem>
<para> <para>
Some <productname>PostgreSQL</productname> error. Some <productname>PostgreSQL</productname> error. The message
The message contains the error message from the contains the error message from the
<productname>PostgreSQL</productname> backend. <productname>PostgreSQL</productname> backend.
</para> </para>
</listitem> </listitem>
...@@ -455,8 +667,8 @@ struct sqlca ...@@ -455,8 +667,8 @@ struct sqlca
<term><computeroutput>-401 (ECPG_TRANS): Error in transaction processing line %d.</computeroutput></term> <term><computeroutput>-401 (ECPG_TRANS): Error in transaction processing line %d.</computeroutput></term>
<listitem> <listitem>
<para> <para>
<productname>PostgreSQL</productname> signaled that we cannot start, <productname>PostgreSQL</productname> signaled that we cannot
commit or rollback the transaction. start, commit, or rollback the transaction.
</para> </para>
</listitem> </listitem>
</varlistentry> </varlistentry>
...@@ -474,40 +686,9 @@ struct sqlca ...@@ -474,40 +686,9 @@ struct sqlca
<term><computeroutput>100 (ECPG_NOT_FOUND): Data not found line %d.</computeroutput></term> <term><computeroutput>100 (ECPG_NOT_FOUND): Data not found line %d.</computeroutput></term>
<listitem> <listitem>
<para> <para>
This is a <quote>normal</quote> error that tells you that what you are querying cannot This is a <quote>normal</quote> error that tells you that what
be found or you are at the end of the cursor. you are querying cannot be found or you are at the end of the
</para> cursor.
</listitem>
</varlistentry>
</variablelist>
</para>
</sect2>
</sect1>
<sect1 id="ecpg-limitations">
<title>Limitations</title>
<para>
What will never be included and why it cannot be done:
<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>
This would require a total redesign of the
<productname>PostgreSQL</productname> access model and the
performance gain does not justify the effort.
</para> </para>
</listitem> </listitem>
</varlistentry> </varlistentry>
...@@ -515,350 +696,229 @@ struct sqlca ...@@ -515,350 +696,229 @@ struct sqlca
</para> </para>
</sect1> </sect1>
<sect1 id="ecpg-porting"> <sect1 id="ecpg-include">
<title>Porting From Other <acronym>RDBMS</acronym> Packages</title> <title>Including Files</title>
<para> <para>
The design of <application>ecpg</application> follows the SQL To include an external file into your embedded SQL program, use:
standard. Porting from a standard RDBMS should not be a problem. <programlisting>
Unfortunately there is no such thing as a standard RDBMS. Therefore EXEC SQL INCLUDE <replaceable>filename</replaceable>;
<application>ecpg</application> tries to understand syntax </programlisting>
extensions as long as they do not create conflicts with the The embedded SQL preprocessor will look for a file named
standard. <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>
<para> <para>
The following list shows all the known incompatibilities. If you Note that this is <emphasis>not</emphasis> the same as
find one not listed please notify the developers. Note, however, that <programlisting>
we list only incompatibilities from a precompiler of another RDBMS #include &lt;<replaceable>filename</replaceable>.h&gt;
to <application>ecpg</application> and not </programlisting>
<application>ecpg</application> features that these RDBMS do not because the file would not be subject to SQL command preprocessing.
support. Naturally, you can continue to use the C
<literal>#include</literal> directive to include other header
files.
</para> </para>
<note>
<para> <para>
<variablelist> The include file name is case-sensitive, even though the rest of
<varlistentry> the <literal>EXEC SQL INCLUDE</literal> command follows the normal
<term>Syntax of FETCH</term> SQL case-sensitivity rules.
<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>
</para> </para>
</note>
</sect1> </sect1>
<sect1 id="ecpg-develop"> <sect1 id="ecpg-process">
<title>For the Developer</title> <title>Processing Embedded SQL Programs</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>.
</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> <para>
Then the preprocessor reads through the file and writes output. Now that you have an idea how to form embedded SQL C programs, you
Normally it just echoes everything to the output. 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> </para>
<para> <para>
When it sees an <command>EXEC SQL</command> statement, it The preprocessor program is called <filename>ecpg</filename> and is
intervenes and changes it. The <command>EXEC SQL</command> included in a normal PostgreSQL installation. Embedded SQL
statement can be one of these: programs are typically named with an extension
<filename>.pgc</filename>. If you have a program file called
<variablelist> <filename>prog1.pgc</filename>, you can preprocess it by simply
<varlistentry> calling
<term>Declare sections</term>
<listitem>
<para>
<command>Declare</> sections begin with:
<programlisting>
exec sql begin declare section;
</programlisting>
and end with:
<programlisting> <programlisting>
exec sql end declare section; ecpg prog1.pgc
</programlisting> </programlisting>
In this section only variable declarations are allowed. Every This will create a file called <filename>prog1.c</filename>. If
variable declared within this section is stored in a list your input files do not follow the suggested naming pattern, you
of variables indexed by name together with its corresponding can specify the output file explicitly using the
type. <option>-o</option> option.
</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>
<para> <para>
The declaration is also echoed to the file to make it a normal The preprocessed file can be compiled normally, for example
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> <programlisting>
VARCHAR var[180]; cc -c prog1.c
</programlisting>
is converted into:
<programlisting>
struct varchar_var { int len; char arr[180]; } var;
</programlisting> </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> </para>
</listitem>
</varlistentry>
<varlistentry>
<term>Include statements</term>
<listitem>
<para> <para>
An include statement looks like: To link an embedded SQL program, you need to include the
<programlisting> <filename>libecpg</filename> library, like so:
exec sql include filename;
</programlisting>
Note that this is NOT the same as:
<programlisting> <programlisting>
#include &lt;filename.h&gt; cc -o myprog prog1.o prog2.o ... -lecpg
</programlisting> </programlisting>
Again, you might have to add an option like
<literal>-L/usr/local/pgsql/lib</literal> to that command line.
</para> </para>
<para> <para>
Instead the file specified is parsed by If you manage the build process of a larger project using
<application>ecpg</application> so the contents of the file are <application>make</application>, it may be convenient to include
included in the resulting C code. This way you are able to the following implicit rule to your makefiles:
specify EXEC SQL commands in an include file.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Connect statement</term>
<listitem>
<para>
A connect statement looks like:
<programlisting> <programlisting>
exec sql connect to <replaceable>connection target</replaceable>; ECPG = ecpg
%.c: %.pgc
$(ECPG) $<
</programlisting> </programlisting>
It creates a connection to the specified database.
</para> </para>
<para> <para>
The <replaceable>connection target</replaceable> can be specified in the The complete syntax of the <command>ecpg</command> command is
following ways: detailed in &cite-reference;.
<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>
</sect1>
<sect1 id="ecpg-library">
<title>Library Functions</title>
<para> <para>
There are also different ways to specify the user name: 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> <itemizedlist>
<listitem> <listitem>
<simpara> <para>
<literal><replaceable>userid</replaceable></literal> <function>ECPGdebug(int <replaceable>on</replaceable>, FILE
</simpara> *<replaceable>stream</replaceable>)</function> turns on debug
</listitem> logging if called with the first argument non-zero. Debug logging
is done on <replaceable>stream</replaceable>. Most
<listitem> <acronym>SQL</acronym> statement log their arguments and results.
<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>
<para> <para>
Finally, the <replaceable>userid</replaceable> and <replaceable>password</replaceable> may be a constant text, a The most important function, <function>ECPGdo</function>, logs
character variable, or a character string. 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> </para>
</listitem> </listitem>
</varlistentry>
<varlistentry>
<term>Disconnect statements</term>
<listitem> <listitem>
<para> <para>
A disconnect statement looks like: <function>ECPGstatus()</function> This method returns true if we
<programlisting> are connected to a database and false if not.
exec sql disconnect [<replaceable>connection target</replaceable>];
</programlisting>
It closes the connection to the specified database.
</para> </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>
</itemizedlist>
</sect1>
<listitem> <sect1 id="ecpg-porting">
<simpara> <title>Porting From Other <acronym>RDBMS</acronym> Packages</title>
<literal>default</literal>
</simpara>
</listitem>
<listitem> <para>
<simpara> The design of <application>ecpg</application> follows the SQL
<literal>current</literal> standard. Porting from a standard RDBMS should not be a problem.
</simpara> Unfortunately there is no such thing as a standard RDBMS. Therefore
</listitem> <application>ecpg</application> tries to understand syntax
extensions as long as they do not create conflicts with the
standard.
</para>
<listitem> <para>
<simpara> The following list shows all the known incompatibilities. If you
<literal>all</literal> find one not listed please notify the developers. Note, however,
</simpara> that we list only incompatibilities from a preprocessor of another
</listitem> RDBMS to <application>ecpg</application> and not
</itemizedlist> <application>ecpg</application> features that these RDBMS do not
support.
</para> </para>
</listitem>
</varlistentry>
<variablelist>
<varlistentry> <varlistentry>
<term>Open cursor statement</term> <term>Syntax of <command>FETCH</command></term>
<indexterm><primary>FETCH</><secondary>embedded SQL</></indexterm>
<listitem> <listitem>
<para> <para>
An open cursor statement looks like: The standard syntax for <command>FETCH</command> is:
<programlisting> <synopsis>
exec sql open <replaceable>cursor</replaceable>; FETCH <optional><replaceable>direction</></> <optional><replaceable>amount</></> IN|FROM <replaceable>cursor</replaceable>
</programlisting> </synopsis>
and is not copied to the output. Instead, the cursor's <indexterm><primary>Oracle</></>
<command>DECLARE</> command is used because it opens the cursor <application>Oracle</application>, however, does not use the
as well. keywords <literal>IN</literal> or <literal>FROM</literal>. This
feature cannot be added since it would create parsing conflicts.
</para> </para>
</listitem> </listitem>
</varlistentry> </varlistentry>
</variablelist>
</sect1>
<sect1 id="ecpg-develop">
<title>For the Developer</title>
<varlistentry>
<term>Commit statement</term>
<listitem>
<para> <para>
A commit statement looks like: This section explain how <application>ecpg</application> works
<programlisting> internally. This information can occasionally be useful to help
exec sql commit; users understand how to use <application>ecpg</application>.
</programlisting>
</para> </para>
</listitem>
</varlistentry>
<varlistentry> <sect2>
<term>Rollback statement</term> <title>The Preprocessor</title>
<listitem>
<para> <para>
A rollback statement looks like: The first four lines written by <command>ecpg</command> to the
<programlisting> output are fixed lines. Two are comments and two are include
exec sql rollback; lines necessary to interface to the library. Then the
</programlisting> preprocessor reads through the file and writes output. Normally
it just echoes everything to the output.
</para> </para>
</listitem>
</varlistentry>
<varlistentry>
<term>Other statements</term>
<listitem>
<para> <para>
Other <acronym>SQL</acronym> statements are used by When it sees an <command>EXEC SQL</command> statement, it
starting with <command>exec sql</command> and ending with intervenes and changes it. The command starts with <command>exec
<command>;</command>. Everything in between is treated as an sql</command> and ends with <command>;</command>. Everything in
<acronym>SQL</acronym> statement and parsed for variable between is treated as an <acronym>SQL</acronym> statement and
substitution. parsed for variable substitution.
</para> </para>
<para> <para>
Variable substitution occurs when a symbol starts with a colon Variable substitution occurs when a symbol starts with a colon
(<command>:</command>). The variable with that name is looked (<literal>:</literal>). The variable with that name is looked up
up among the variables that were previously declared within a among the variables that were previously declared within a
<command>declare</> section. Depending on whether the variable is <literal>EXEC SQL DECLARE</> section. Depending on whether the
being use for input or output, a pointer to the variable is variable is being use for input or output, a pointer to the
output to allow access by the function. variable is output to allow access by the function.
</para> </para>
<para> <para>
...@@ -904,13 +964,14 @@ exec sql rollback; ...@@ -904,13 +964,14 @@ exec sql rollback;
<listitem> <listitem>
<para> <para>
A pointer to the value of the indicator variable or a pointer to the pointer of the indicator variable. A pointer to the value of the indicator variable or a pointer
to the pointer of the indicator variable.
</para> </para>
</listitem> </listitem>
<listitem> <listitem>
<para> <para>
0. 0
</para> </para>
</listitem> </listitem>
...@@ -929,25 +990,28 @@ exec sql rollback; ...@@ -929,25 +990,28 @@ exec sql rollback;
</itemizedlist> </itemizedlist>
</para> </para>
</listitem> <para>
</varlistentry> Note that not all SQL commands are treated in this way. For
</variablelist> 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 because it opens the cursor as
well.
</para> </para>
</sect2>
<sect2>
<title>A Complete Example</title>
<para> <para>
Here is a complete example describing the output of the preprocessor of a Here is a complete example describing the output of the
file <filename>foo.pgc</filename>: preprocessor of a file <filename>foo.pgc</filename> (details may
change with each particular version of the preprocessor):
<programlisting> <programlisting>
exec sql begin declare section; EXEC SQL BEGIN DECLARE SECTION;
int index; int index;
int result; 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> </programlisting>
is translated into: is translated into:
<programlisting> <programlisting>
...@@ -964,7 +1028,7 @@ exec sql select res into :result from mytable where index = :index; ...@@ -964,7 +1028,7 @@ exec sql select res into :result from mytable where index = :index;
int result; int result;
/* exec sql end declare section */ /* 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_int,&amp;(index),1L,1L,sizeof(int),
ECPGt_NO_INDICATOR, NULL , 0L, 0L, 0L, ECPGt_EOIT, ECPGt_NO_INDICATOR, NULL , 0L, 0L, 0L, ECPGt_EOIT,
ECPGt_int,&amp;(result),1L,1L,sizeof(int), ECPGt_int,&amp;(result),1L,1L,sizeof(int),
...@@ -982,9 +1046,10 @@ ECPGdo(__LINE__, NULL, "select res from mytable where index = ? ", ...@@ -982,9 +1046,10 @@ ECPGdo(__LINE__, NULL, "select res from mytable where index = ? ",
<para> <para>
The most important function in the library is The most important function in the library is
<function>ECPGdo</function>. It takes a variable number of <function>ECPGdo</function>. It takes a variable number of
arguments. Hopefully there are no computers that limit the arguments. Hopefully there are no computers that limit the number
number of variables that can be accepted by a <function>varargs()</function> function. This of variables that can be accepted by a
can easily add up to 50 or so arguments. <function>varargs()</function> function. This can easily add up to
50 or so arguments.
</para> </para>
<para> <para>
...@@ -995,7 +1060,8 @@ ECPGdo(__LINE__, NULL, "select res from mytable where index = ? ", ...@@ -995,7 +1060,8 @@ ECPGdo(__LINE__, NULL, "select res from mytable where index = ? ",
<term>A line number</term> <term>A line number</term>
<listitem> <listitem>
<para> <para>
This is a line number of the original line; used in error messages only. This is a line number of the original line; used in error
messages only.
</para> </para>
</listitem> </listitem>
</varlistentry> </varlistentry>
...@@ -1017,8 +1083,8 @@ ECPGdo(__LINE__, NULL, "select res from mytable where index = ? ", ...@@ -1017,8 +1083,8 @@ ECPGdo(__LINE__, NULL, "select res from mytable where index = ? ",
<term>Input variables</term> <term>Input variables</term>
<listitem> <listitem>
<para> <para>
As described in the section about the preprocessor, every input variable As described in the section about the preprocessor, every
gets ten arguments. input variable gets ten arguments.
</para> </para>
</listitem> </listitem>
</varlistentry> </varlistentry>
...@@ -1027,7 +1093,8 @@ ECPGdo(__LINE__, NULL, "select res from mytable where index = ? ", ...@@ -1027,7 +1093,8 @@ ECPGdo(__LINE__, NULL, "select res from mytable where index = ? ",
<term><parameter>ECPGt_EOIT</></term> <term><parameter>ECPGt_EOIT</></term>
<listitem> <listitem>
<para> <para>
An <type>enum</> telling that there are no more input variables. An <type>enum</> telling that there are no more input
variables.
</para> </para>
</listitem> </listitem>
</varlistentry> </varlistentry>
...@@ -1036,8 +1103,9 @@ ECPGdo(__LINE__, NULL, "select res from mytable where index = ? ", ...@@ -1036,8 +1103,9 @@ ECPGdo(__LINE__, NULL, "select res from mytable where index = ? ",
<term>Output variables</term> <term>Output variables</term>
<listitem> <listitem>
<para> <para>
As described in the section about the preprocessor, every input variable As described in the section about the preprocessor, every
gets ten arguments. These variables are filled by the function. input variable gets ten arguments. These variables are filled
by the function.
</para> </para>
</listitem> </listitem>
</varlistentry> </varlistentry>
...@@ -1052,21 +1120,9 @@ ECPGdo(__LINE__, NULL, "select res from mytable where index = ? ", ...@@ -1052,21 +1120,9 @@ ECPGdo(__LINE__, NULL, "select res from mytable where index = ? ",
</varlistentry> </varlistentry>
</variablelist> </variablelist>
</para> </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> </sect2>
</sect1> </sect1>
</chapter> </chapter>
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<!-- <!--
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PostgreSQL documentation PostgreSQL documentation
--> -->
<refentry id="APP-ECPG"> <refentry id="APP-ECPG">
<refmeta> <refmeta>
<refentrytitle id="app-ecpg-title"><application>ecpg</application></refentrytitle> <refentrytitle><application>ecpg</application></refentrytitle>
<manvolnum>1</manvolnum> <manvolnum>1</manvolnum>
<refmiscinfo>Application</refmiscinfo> <refmiscinfo>Application</refmiscinfo>
</refmeta> </refmeta>
<refnamediv> <refnamediv>
<refname> <refname><application>ecpg</application></refname>
<application>ecpg</application> <refpurpose>embedded SQL C preprocessor</refpurpose>
</refname>
<refpurpose>
embedded SQL C preprocessor
</refpurpose>
</refnamediv> </refnamediv>
<refsynopsisdiv> <refsynopsisdiv>
<refsynopsisdivinfo>
<date>1999-07-20</date>
</refsynopsisdivinfo>
<cmdsynopsis> <cmdsynopsis>
<command>ecpg</command> <command>ecpg</command>
<arg choice="opt">-v</arg> <arg choice="opt" rep="repeat"><replaceable>option</replaceable></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="plain" rep="repeat"><replaceable>file</replaceable></arg> <arg choice="plain" rep="repeat"><replaceable>file</replaceable></arg>
</cmdsynopsis> </cmdsynopsis>
</refsynopsisdiv> </refsynopsisdiv>
<refsect1 id="APP-ECPG-description"> <refsect1 id="APP-ECPG-description">
<title>Description</title> <title>Description</title>
<para> <para>
<application>ecpg</application> <command>ecpg</command> is the embedded SQL preprocessor for C
is an embedded SQL preprocessor for the C language and the programs. It converts C programs with embedded SQL statements to
<productname>PostgreSQL</productname>. It normal C code by replacing the SQL invocations with special
enables development of C programs with embedded SQL code. function calls. The output files can then be processed with any C
compiler tool chain.
</para> </para>
<para> <para>
Linus Tolke (<email>linus@epact.se</email>) was the <command>ecpg</command> will convert each input file given on the
original author of <application>ecpg</application> (up to version 0.2). command line to the corresponding C output file. Input files
Michael Meskes (<email>meskes@debian.org</email>) preferrably have the extension <filename>.pgc</filename>, in which
is the current author and maintainer of <application>ecpg</application>. case the extension will be replaced by <filename>.c</filename> to
Thomas Good (<email>tomg@q8.nrnet.org</email>) determine the output file name. If the extension of the input file
is the author of the last revision of the <application>ecpg</application> man page, on which is not <filename>.pgc</filename>, then the output file name is
this document is based. 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>
<para>
This reference page does not describe the embedded SQL language.
See &cite-programmer; for that.
</para> </para>
</refsect1> </refsect1>
...@@ -59,338 +58,137 @@ PostgreSQL documentation ...@@ -59,338 +58,137 @@ PostgreSQL documentation
<title>Options</title> <title>Options</title>
<para> <para>
<application>ecpg</application> accepts the following command <command>ecpg</command> accepts the following command-line
line arguments: arguments:
<variablelist> <variablelist>
<varlistentry> <varlistentry>
<term>-v</term> <term><option>-c</option></term>
<listitem> <listitem>
<para> <para>
Print version information. Automatically generate C code from SQL code. Currently, this
works for <literal>EXEC SQL TYPE</literal>.
</para> </para>
</listitem> </listitem>
</varlistentry> </varlistentry>
<varlistentry> <varlistentry>
<term>-t</term> <term><option>-D <replaceable>symbol</replaceable></option></term>
<listitem> <listitem>
<para> <para>
Turn on auto-commit of transactions. In this mode, each query is Define a C preprocessor symbol.
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> </para>
</listitem> </listitem>
</varlistentry> </varlistentry>
<varlistentry> <varlistentry>
<term>-I <replaceable class="parameter">include-path</replaceable></term> <term><option>-I <replaceable class="parameter">directory</replaceable></option></term>
<listitem> <listitem>
<para> <para>
Specify an additional include path. Specify an additional include path, used to find files included
Defaults are <filename>.</filename> (current directory), via <literal>EXEC SQL INCLUDE</literal>. Defaults are
<filename>.</filename> (current directory),
<filename>/usr/local/include</filename>, the <filename>/usr/local/include</filename>, the
<productname>PostgreSQL</productname> include path which is <productname>PostgreSQL</productname> include directory which
defined at compile time (default: is defined at compile time (default:
<filename>/usr/local/pgsql/include</filename>), and <filename>/usr/local/pgsql/include</filename>), and
<filename>/usr/include</filename>. <filename>/usr/include</filename>, in that order.
</para> </para>
</listitem> </listitem>
</varlistentry> </varlistentry>
<varlistentry> <varlistentry>
<term>-o <replaceable>outfile</replaceable></term> <term><option>-o <replaceable>filename</replaceable></option></term>
<listitem> <listitem>
<para> <para>
Specifies that <application>ecpg</application> should write all its output to <replaceable>outfile</replaceable>. Specifies that <application>ecpg</application> should write all
If no such option is given the output is written to its output to the given <replaceable>filename</replaceable>.
<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> </para>
</listitem> </listitem>
</varlistentry> </varlistentry>
<varlistentry> <varlistentry>
<term><replaceable class="parameter">file</replaceable></term> <term><option>-t</option></term>
<listitem> <listitem>
<para> <para>
The files to be processed. 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> </para>
</listitem> </listitem>
</varlistentry> </varlistentry>
</variablelist>
</para>
</refsect1>
<refsect1>
<title>Exit Status</title>
<varlistentry>
<term><option>-v</option></term>
<listitem>
<para> <para>
<application>ecpg</application> returns 0 to the shell on Print additional information including the version and the
successful completion, non-zero for errors. include path.
</para> </para>
</refsect1> </listitem>
</varlistentry>
<refsect1>
<title>Usage</title>
<refsect2 id="APP-ECPG-preprocessing">
<title>Preprocessing for Compilation</title>
<varlistentry>
<term><option>---help</option></term>
<listitem>
<para> <para>
An embedded SQL source file must be preprocessed before Show a brief summary of the command usage, then exit.
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>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--version</option></term>
<listitem>
<para> <para>
You may want to redirect the preprocessor output to a log file. Output version information, then exit.
</para> </para>
</refsect2> </listitem>
</varlistentry>
<refsect2 id="APP-ECPG-compiling"> </variablelist>
<title>Compiling and Linking</title>
<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:
<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> </para>
</refsect2>
</refsect1> </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"> <refsect1>
<title>Variable Declaration</title> <title>Notes</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> <para>
Create Table: When compiling the preprocessed C code files, the compiler needs to
be able to find the <application>ECPG</> header files in the
<programlisting> PostgreSQL include directory. Therefore, one might have to use the
EXEC SQL CREATE TABLE foo (number int4, ascii char(16)); <option>-I</> option when invoking the compiler (e.g.,
EXEC SQL CREATE UNIQUE index num1 on foo(number); <literal>-I/usr/local/pgsql/include</literal>).
EXEC SQL COMMIT;
</programlisting>
</para> </para>
<para> <para>
Insert: Programs using C code with embedded SQL have to be linked against
the <filename>libecpg</filename> library, for example using the
<programlisting> flags <literal>-L/usr/local/pgsql/lib -lecpg</literal>.
EXEC SQL INSERT INTO foo (number, ascii) VALUES (9999, 'doodad');
EXEC SQL COMMIT;
</programlisting>
</para> </para>
<para> <para>
Delete: The value of either of these directories that is appropriate for
the installation can be found out using <xref
<programlisting> linkend="app-pgconfig">.
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>
</refsect1>
<para>
Select using Cursors:
<programlisting> <refsect1>
EXEC SQL DECLARE foo_bar CURSOR FOR <title>Examples</title>
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> <para>
Updates: 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> <programlisting>
EXEC SQL UPDATE foo ecpg prog1.pgc
SET ascii = 'foobar' cc -I/usr/local/pgsql/include -c prog1.c
WHERE number = 9999; cc -o prog1 prog1.o -L/usr/local/pgsql/lib -lecpg
EXEC SQL COMMIT;
</programlisting> </programlisting>
</para> </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> </refsect1>
...@@ -399,7 +197,7 @@ EXEC SQL COMMIT; ...@@ -399,7 +197,7 @@ EXEC SQL COMMIT;
<para> <para>
<citetitle>PostgreSQL Programmer's Guide</citetitle> for a more <citetitle>PostgreSQL Programmer's Guide</citetitle> for a more
detailed description of the embedded SQL interface. detailed description of the embedded SQL interface
</para> </para>
</refsect1> </refsect1>
......
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