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 | 
<a href="#id2972565" class="shortcut">Description</a></nobr></td></tr>
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<div class="refentry" lang="en">
<a name="glib-Warnings-and-Assertions"></a><div class="titlepage"></div>
<div class="refnamediv"><table width="100%"><tr>
<td valign="top">
<h2>
<a name="id2972332"></a><span class="refentrytitle">Message Output and Debugging Functions</span>
</h2>
<p>Message Output and Debugging Functions — functions to output messages and help debug applications.</p>
</td>
<td valign="top" align="right"></td>
</tr></table></div>
<div class="refsynopsisdiv">
<h2>Synopsis</h2>
<pre class="synopsis">
#include <glib.h>
void <a href="glib-Warnings-and-Assertions.html#g-print">g_print</a> (const <a href="glib-Basic-Types.html#gchar">gchar</a> *format,
...);
<a href="glib-Warnings-and-Assertions.html#GPrintFunc">GPrintFunc</a> <a href="glib-Warnings-and-Assertions.html#g-set-print-handler">g_set_print_handler</a> (<a href="glib-Warnings-and-Assertions.html#GPrintFunc">GPrintFunc</a> func);
void (<a href="glib-Warnings-and-Assertions.html#GPrintFunc">*GPrintFunc</a>) (const <a href="glib-Basic-Types.html#gchar">gchar</a> *string);
void <a href="glib-Warnings-and-Assertions.html#g-printerr">g_printerr</a> (const <a href="glib-Basic-Types.html#gchar">gchar</a> *format,
...);
<a href="glib-Warnings-and-Assertions.html#GPrintFunc">GPrintFunc</a> <a href="glib-Warnings-and-Assertions.html#g-set-printerr-handler">g_set_printerr_handler</a> (<a href="glib-Warnings-and-Assertions.html#GPrintFunc">GPrintFunc</a> func);
#define <a href="glib-Warnings-and-Assertions.html#g-return-if-fail">g_return_if_fail</a> (expr)
#define <a href="glib-Warnings-and-Assertions.html#g-return-val-if-fail">g_return_val_if_fail</a> (expr,val)
#define <a href="glib-Warnings-and-Assertions.html#g-return-if-reached">g_return_if_reached</a> ()
#define <a href="glib-Warnings-and-Assertions.html#g-return-val-if-reached">g_return_val_if_reached</a> (val)
#define <a href="glib-Warnings-and-Assertions.html#g-assert">g_assert</a> (expr)
#define <a href="glib-Warnings-and-Assertions.html#g-assert-not-reached">g_assert_not_reached</a> ()
void <a href="glib-Warnings-and-Assertions.html#g-on-error-query">g_on_error_query</a> (const <a href="glib-Basic-Types.html#gchar">gchar</a> *prg_name);
void <a href="glib-Warnings-and-Assertions.html#g-on-error-stack-trace">g_on_error_stack_trace</a> (const <a href="glib-Basic-Types.html#gchar">gchar</a> *prg_name);
#define <a href="glib-Warnings-and-Assertions.html#G-BREAKPOINT:CAPS">G_BREAKPOINT</a> ()
</pre>
</div>
<div class="refsect1" lang="en">
<a name="id2972565"></a><h2>Description</h2>
<p>
These functions provide support for outputting messages.
</p>
</div>
<div class="refsect1" lang="en">
<a name="id2972580"></a><h2>Details</h2>
<div class="refsect2" lang="en">
<a name="id2972590"></a><h3>
<a name="g-print"></a>g_print ()</h3>
<a class="indexterm" name="id2972603"></a><pre class="programlisting">void g_print (const <a href="glib-Basic-Types.html#gchar">gchar</a> *format,
...);</pre>
<p>
Outputs a formatted message via the print handler.
The default print handler simply outputs the message to stdout.
</p>
<p>
<a href="glib-Warnings-and-Assertions.html#g-print"><code class="function">g_print()</code></a> should not be used from within libraries for debugging messages,
since it may be redirected by applications to special purpose message
windows or even files.
Instead, libraries should use <a href="glib-Message-Logging.html#g-log"><code class="function">g_log()</code></a>, or the convenience functions
<a href="glib-Message-Logging.html#g-message"><code class="function">g_message()</code></a>, <a href="glib-Message-Logging.html#g-warning"><code class="function">g_warning()</code></a> and <a href="glib-Message-Logging.html#g-error"><code class="function">g_error()</code></a>.
</p>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td>
<span class="term"><em class="parameter"><code>format</code></em> :</span></td>
<td>the message format. See the <code class="function"><code class="function">printf()</code></code>
documentation.
</td>
</tr>
<tr>
<td>
<span class="term"><em class="parameter"><code>...</code></em> :</span></td>
<td>the parameters to insert into the format string.
</td>
</tr>
</tbody>
</table></div>
</div>
<hr>
<div class="refsect2" lang="en">
<a name="id2972744"></a><h3>
<a name="g-set-print-handler"></a>g_set_print_handler ()</h3>
<a class="indexterm" name="id2972757"></a><pre class="programlisting"><a href="glib-Warnings-and-Assertions.html#GPrintFunc">GPrintFunc</a> g_set_print_handler (<a href="glib-Warnings-and-Assertions.html#GPrintFunc">GPrintFunc</a> func);</pre>
<p>
Sets the print handler.
Any messages passed to <a href="glib-Warnings-and-Assertions.html#g-print"><code class="function">g_print()</code></a> will be output via the new handler.
The default handler simply outputs the message to stdout.
By providing your own handler you can redirect the output, to a GTK+
widget or a log file for example.
</p>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td>
<span class="term"><em class="parameter"><code>func</code></em> :</span></td>
<td>the new print handler.
</td>
</tr>
<tr>
<td>
<span class="term"><span class="emphasis"><em>Returns</em></span> :</span></td>
<td>the old print handler.
</td>
</tr>
</tbody>
</table></div>
</div>
<hr>
<div class="refsect2" lang="en">
<a name="id2972828"></a><h3>
<a name="GPrintFunc"></a>GPrintFunc ()</h3>
<a class="indexterm" name="id2972841"></a><pre class="programlisting">void (*GPrintFunc) (const <a href="glib-Basic-Types.html#gchar">gchar</a> *string);</pre>
<p>
Specifies the type of the print handler functions.
These are called with the complete formatted string to output.
</p>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody><tr>
<td>
<span class="term"><em class="parameter"><code>string</code></em> :</span></td>
<td>the message to be output.
</td>
</tr></tbody>
</table></div>
</div>
<hr>
<div class="refsect2" lang="en">
<a name="id2972889"></a><h3>
<a name="g-printerr"></a>g_printerr ()</h3>
<a class="indexterm" name="id2972902"></a><pre class="programlisting">void g_printerr (const <a href="glib-Basic-Types.html#gchar">gchar</a> *format,
...);</pre>
<p>
Outputs a formatted message via the error message handler.
The default handler simply outputs the message to stderr.
</p>
<p>
<a href="glib-Warnings-and-Assertions.html#g-printerr"><code class="function">g_printerr()</code></a> should not be used from within libraries. Instead <a href="glib-Message-Logging.html#g-log"><code class="function">g_log()</code></a> should
be used, or the convenience functions <a href="glib-Message-Logging.html#g-message"><code class="function">g_message()</code></a>, <a href="glib-Message-Logging.html#g-warning"><code class="function">g_warning()</code></a> and <a href="glib-Message-Logging.html#g-error"><code class="function">g_error()</code></a>.
</p>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td>
<span class="term"><em class="parameter"><code>format</code></em> :</span></td>
<td>the message format. See the <code class="function"><code class="function">printf()</code></code>
documentation.
</td>
</tr>
<tr>
<td>
<span class="term"><em class="parameter"><code>...</code></em> :</span></td>
<td>the parameters to insert into the format string.
</td>
</tr>
</tbody>
</table></div>
</div>
<hr>
<div class="refsect2" lang="en">
<a name="id2973035"></a><h3>
<a name="g-set-printerr-handler"></a>g_set_printerr_handler ()</h3>
<a class="indexterm" name="id2973048"></a><pre class="programlisting"><a href="glib-Warnings-and-Assertions.html#GPrintFunc">GPrintFunc</a> g_set_printerr_handler (<a href="glib-Warnings-and-Assertions.html#GPrintFunc">GPrintFunc</a> func);</pre>
<p>
Sets the handler for printing error messages.
Any messages passed to <a href="glib-Warnings-and-Assertions.html#g-printerr"><code class="function">g_printerr()</code></a> will be output via the new handler.
The default handler simply outputs the message to stderr.
By providing your own handler you can redirect the output, to a GTK+
widget or a log file for example.
</p>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td>
<span class="term"><em class="parameter"><code>func</code></em> :</span></td>
<td>the new error message handler.
</td>
</tr>
<tr>
<td>
<span class="term"><span class="emphasis"><em>Returns</em></span> :</span></td>
<td>the old error message handler.
</td>
</tr>
</tbody>
</table></div>
</div>
<hr>
<div class="refsect2" lang="en">
<a name="id2973121"></a><h3>
<a name="g-return-if-fail"></a>g_return_if_fail()</h3>
<a class="indexterm" name="id2973134"></a><pre class="programlisting">#define g_return_if_fail(expr)</pre>
<p>
Returns from the current function if the expression is not true.
If the expression evaluates to <a href="glib-Standard-Macros.html#FALSE:CAPS"><code class="literal">FALSE</code></a>, a critical message is logged and
the function returns. This can only be used in functions which do not return
a value.
</p>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody><tr>
<td>
<span class="term"><em class="parameter"><code>expr</code></em> :</span></td>
<td>the expression to check.
</td>
</tr></tbody>
</table></div>
</div>
<hr>
<div class="refsect2" lang="en">
<a name="id2973181"></a><h3>
<a name="g-return-val-if-fail"></a>g_return_val_if_fail()</h3>
<a class="indexterm" name="id2973194"></a><pre class="programlisting">#define g_return_val_if_fail(expr,val)</pre>
<p>
Returns from the current function, returning the value <em class="parameter"><code>val</code></em>, if the expression
is not true.
If the expression evaluates to <a href="glib-Standard-Macros.html#FALSE:CAPS"><code class="literal">FALSE</code></a>, a critical message is logged and
<em class="parameter"><code>val</code></em> is returned.
</p>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td>
<span class="term"><em class="parameter"><code>expr</code></em> :</span></td>
<td>the expression to check.
</td>
</tr>
<tr>
<td>
<span class="term"><em class="parameter"><code>val</code></em> :</span></td>
<td>the value to return from the current function if the expression is not
true.
</td>
</tr>
</tbody>
</table></div>
</div>
<hr>
<div class="refsect2" lang="en">
<a name="id2973266"></a><h3>
<a name="g-return-if-reached"></a>g_return_if_reached()</h3>
<a class="indexterm" name="id2973280"></a><pre class="programlisting">#define g_return_if_reached()</pre>
<p>
Logs a critical message and returns from the current function.
This can only be used in functions which do not return a value.
</p>
</div>
<hr>
<div class="refsect2" lang="en">
<a name="id2973297"></a><h3>
<a name="g-return-val-if-reached"></a>g_return_val_if_reached()</h3>
<a class="indexterm" name="id2973310"></a><pre class="programlisting">#define g_return_val_if_reached(val)</pre>
<p>
Logs a critical message and returns <em class="parameter"><code>val</code></em>.
</p>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody><tr>
<td>
<span class="term"><em class="parameter"><code>val</code></em> :</span></td>
<td>the value to return from the current function.
</td>
</tr></tbody>
</table></div>
</div>
<hr>
<div class="refsect2" lang="en">
<a name="id2973350"></a><h3>
<a name="g-assert"></a>g_assert()</h3>
<a class="indexterm" name="id2973362"></a><pre class="programlisting">#define g_assert(expr)</pre>
<p>
Debugging macro to terminate the application if the assertion fails.
If the assertion fails (i.e. the expression is not true), an error message
is logged and the application is terminated.
</p>
<p>
The macro can be turned off in final releases of code by defining
<span class="type">G_DISABLE_ASSERT</span> when compiling the application.
</p>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody><tr>
<td>
<span class="term"><em class="parameter"><code>expr</code></em> :</span></td>
<td>the expression to check.
</td>
</tr></tbody>
</table></div>
</div>
<hr>
<div class="refsect2" lang="en">
<a name="id2973414"></a><h3>
<a name="g-assert-not-reached"></a>g_assert_not_reached()</h3>
<a class="indexterm" name="id2973427"></a><pre class="programlisting">#define g_assert_not_reached()</pre>
<p>
Debugging macro to terminate the application if it is ever reached.
If it is reached, an error message is logged and the application is terminated.
</p>
<p>
The macro can be turned off in final releases of code by defining
<span class="type">G_DISABLE_ASSERT</span> when compiling the application.
</p>
</div>
<hr>
<div class="refsect2" lang="en">
<a name="id2973459"></a><h3>
<a name="g-on-error-query"></a>g_on_error_query ()</h3>
<a class="indexterm" name="id2973472"></a><pre class="programlisting">void g_on_error_query (const <a href="glib-Basic-Types.html#gchar">gchar</a> *prg_name);</pre>
<p>
Prompts the user with <code class="computeroutput">[E]xit, [H]alt, show [S]tack trace or [P]roceed</code>.
This function is intended to be used for debugging use only. The following
example shows how it can be used together with the <a href="glib-Message-Logging.html#g-log"><code class="function">g_log()</code></a> functions.
</p>
<div class="informalexample"><pre class="programlisting">
#include <glib.h>
static void
log_handler (const gchar *log_domain,
GLogLevelFlags log_level,
const gchar *message,
gpointer user_data)
{
g_log_default_handler (log_domain, log_level, message, user_data);
g_on_error_query (MY_PROGRAM_NAME);
}
int main (int argc, char *argv[])
{
g_log_set_handler (MY_LOG_DOMAIN,
G_LOG_LEVEL_WARNING |
G_LOG_LEVEL_ERROR |
G_LOG_LEVEL_CRITICAL,
log_handler,
NULL);
/* ... */
</pre></div>
<p>
If [E]xit is selected, the application terminates with a call to
<code class="function">_exit(0)</code>.
</p>
<p>
If [H]alt is selected, the application enters an infinite loop.
The infinite loop can only be stopped by killing the application,
or by setting <span class="type">glib_on_error_halt</span> to <a href="glib-Standard-Macros.html#FALSE:CAPS"><code class="literal">FALSE</code></a> (possibly via a debugger).
</p>
<p>
If [S]tack trace is selected, <a href="glib-Warnings-and-Assertions.html#g-on-error-stack-trace"><code class="function">g_on_error_stack_trace()</code></a> is called. This
invokes <span><strong class="command">gdb</strong></span>, which attaches to the current process and shows a stack trace.
The prompt is then shown again.
</p>
<p>
If [P]roceed is selected, the function returns.
</p>
<p>
This function may cause different actions on non-UNIX platforms.
</p>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody><tr>
<td>
<span class="term"><em class="parameter"><code>prg_name</code></em> :</span></td>
<td>the program name, needed by <span><strong class="command">gdb</strong></span> for the [S]tack trace option.
If <em class="parameter"><code>prg_name</code></em> is <a href="glib-Standard-Macros.html#NULL:CAPS"><code class="literal">NULL</code></a>, <a href="glib-Miscellaneous-Utility-Functions.html#g-get-prgname"><code class="function">g_get_prgname()</code></a> is called to get the program name
(which will work correctly if <a
href="../gdk/gdk-General.html#gdk-init"
><code class="function">gdk_init()</code></a> or <a
href="../gtk/gtk-General.html#gtk-init"
><code class="function">gtk_init()</code></a> has been called).
</td>
</tr></tbody>
</table></div>
</div>
<hr>
<div class="refsect2" lang="en">
<a name="id2973689"></a><h3>
<a name="g-on-error-stack-trace"></a>g_on_error_stack_trace ()</h3>
<a class="indexterm" name="id2973702"></a><pre class="programlisting">void g_on_error_stack_trace (const <a href="glib-Basic-Types.html#gchar">gchar</a> *prg_name);</pre>
<p>
Invokes <span><strong class="command">gdb</strong></span>, which attaches to the current process and shows a stack trace.
Called by <a href="glib-Warnings-and-Assertions.html#g-on-error-query"><code class="function">g_on_error_query()</code></a> when the [S]tack trace option is selected.
</p>
<p>
This function may cause different actions on non-UNIX platforms.
</p>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody><tr>
<td>
<span class="term"><em class="parameter"><code>prg_name</code></em> :</span></td>
<td>the program name, needed by <span><strong class="command">gdb</strong></span> for the [S]tack trace option.
If <em class="parameter"><code>prg_name</code></em> is <a href="glib-Standard-Macros.html#NULL:CAPS"><code class="literal">NULL</code></a>, <a href="glib-Miscellaneous-Utility-Functions.html#g-get-prgname"><code class="function">g_get_prgname()</code></a> is called to get the program name
(which will work correctly if <a
href="../gdk/gdk-General.html#gdk-init"
><code class="function">gdk_init()</code></a> or <a
href="../gtk/gtk-General.html#gtk-init"
><code class="function">gtk_init()</code></a> has been called).
</td>
</tr></tbody>
</table></div>
</div>
<hr>
<div class="refsect2" lang="en">
<a name="id2973826"></a><h3>
<a name="G-BREAKPOINT:CAPS"></a>G_BREAKPOINT()</h3>
<a class="indexterm" name="id2973839"></a><pre class="programlisting">#define G_BREAKPOINT()</pre>
<p>
Inserts a breakpoint instruction into the code (on x86 machines only).
</p>
</div>
</div>
</div>
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