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Peter Eisentraut 24 years ago
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  1. 1964
      doc/src/sgml/ecpg.sgml
  2. 486
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<!--
$Header: /cvsroot/pgsql/doc/src/sgml/ref/ecpg-ref.sgml,v 1.20 2002/07/28 15:22:20 petere Exp $
$Header: /cvsroot/pgsql/doc/src/sgml/ref/ecpg-ref.sgml,v 1.21 2002/10/21 18:04:05 petere Exp $
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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