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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>34.12. Notice Processing</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><link rel="prev" href="libpq-misc.html" title="34.11. Miscellaneous Functions" /><link rel="next" href="libpq-events.html" title="34.13. Event System" /></head><body><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">34.12. Notice Processing</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="libpq-misc.html" title="34.11. Miscellaneous Functions">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="libpq.html" title="Chapter 34. libpq - C Library">Up</a></td><th width="60%" align="center">Chapter 34. <span xmlns="http://www.w3.org/1999/xhtml" class="application">libpq</span> - C Library</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 11.5 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="libpq-events.html" title="34.13. Event System">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="LIBPQ-NOTICE-PROCESSING"><div class="titlepage"><div><div><h2 class="title" style="clear: both">34.12. Notice Processing</h2></div></div></div><a id="id-1.7.3.19.2" class="indexterm"></a><p>
Notice and warning messages generated by the server are not returned
by the query execution functions, since they do not imply failure of
the query. Instead they are passed to a notice handling function, and
execution continues normally after the handler returns. The default
notice handling function prints the message on
<code class="filename">stderr</code>, but the application can override this
behavior by supplying its own handling function.
</p><p>
For historical reasons, there are two levels of notice handling, called
the notice receiver and notice processor. The default behavior is for
the notice receiver to format the notice and pass a string to the notice
processor for printing. However, an application that chooses to provide
its own notice receiver will typically ignore the notice processor
layer and just do all the work in the notice receiver.
</p><p>
The function <code class="function">PQsetNoticeReceiver</code>
<a id="id-1.7.3.19.5.2" class="indexterm"></a>
<a id="id-1.7.3.19.5.3" class="indexterm"></a> sets or
examines the current notice receiver for a connection object.
Similarly, <code class="function">PQsetNoticeProcessor</code>
<a id="id-1.7.3.19.5.5" class="indexterm"></a>
<a id="id-1.7.3.19.5.6" class="indexterm"></a> sets or
examines the current notice processor.
</p><pre class="synopsis">
typedef void (*PQnoticeReceiver) (void *arg, const PGresult *res);
PQnoticeReceiver
PQsetNoticeReceiver(PGconn *conn,
PQnoticeReceiver proc,
void *arg);
typedef void (*PQnoticeProcessor) (void *arg, const char *message);
PQnoticeProcessor
PQsetNoticeProcessor(PGconn *conn,
PQnoticeProcessor proc,
void *arg);
</pre><p>
Each of these functions returns the previous notice receiver or
processor function pointer, and sets the new value. If you supply a
null function pointer, no action is taken, but the current pointer is
returned.
</p><p>
When a notice or warning message is received from the server, or
generated internally by <span class="application">libpq</span>, the notice
receiver function is called. It is passed the message in the form of
a <code class="symbol">PGRES_NONFATAL_ERROR</code>
<code class="structname">PGresult</code>. (This allows the receiver to extract
individual fields using <code class="function">PQresultErrorField</code>, or obtain a
complete preformatted message using <code class="function">PQresultErrorMessage</code>
or <code class="function">PQresultVerboseErrorMessage</code>.) The same
void pointer passed to <code class="function">PQsetNoticeReceiver</code> is also
passed. (This pointer can be used to access application-specific state
if needed.)
</p><p>
The default notice receiver simply extracts the message (using
<code class="function">PQresultErrorMessage</code>) and passes it to the notice
processor.
</p><p>
The notice processor is responsible for handling a notice or warning
message given in text form. It is passed the string text of the message
(including a trailing newline), plus a void pointer that is the same
one passed to <code class="function">PQsetNoticeProcessor</code>. (This pointer
can be used to access application-specific state if needed.)
</p><p>
The default notice processor is simply:
</p><pre class="programlisting">
static void
defaultNoticeProcessor(void *arg, const char *message)
{
fprintf(stderr, "%s", message);
}
</pre><p>
</p><p>
Once you have set a notice receiver or processor, you should expect
that that function could be called as long as either the
<code class="structname">PGconn</code> object or <code class="structname">PGresult</code> objects made
from it exist. At creation of a <code class="structname">PGresult</code>, the
<code class="structname">PGconn</code>'s current notice handling pointers are copied
into the <code class="structname">PGresult</code> for possible use by functions like
<code class="function">PQgetvalue</code>.
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