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<chapter id="extend">

<title>Extending <acronym>SQL</acronym></title>

&xoper;

&xindex;

<sect1 id="extend-how">

<title>Using C++ for Extensibility</title>

<indexterm zone="extend-Cpp">

<primary>C++</primary>

</indexterm>

<para>

It is possible to use a compiler in C++ mode to build

<productname>PostgreSQL</productname> extensions; you must simply

follow the standard methods for dynamically linking to C executables:

<itemizedlist>

<listitem>

<para>

Use <literal>extern C</> linkage for all functions that must

be accessible by <function>dlopen()</>. This is also necessary

for any functions that might be passed as pointers between

the backend and C++ code.

</para>

</listitem>

<listitem>

<para>

Use <function>malloc()</> to allocate any memory that might be

freed by the backend C code (don't pass <function>new()</>-allocated

memory).

</para>

</listitem>

<listitem>

<para>

Use <function>free()</> to free memory allocated by the backend

C code (do not use <function>delete()</> for such cases).

</para>

</listitem>

<listitem>

<para>

Prevent exceptions from propagating into the C code (use a

catch-all block at the top level of all <literal>extern C</>

functions).

</para>

</listitem>

</itemizedlist>

</para>

</sect1>

</chapter>