<refentry id="glib-running" revision="17 Jan 2002"><refmeta><refentrytitle>Running GLib Applications</refentrytitle><manvolnum>3</manvolnum><refmiscinfo>GLib Library</refmiscinfo></refmeta><refnamediv><refname>Running GLib Applications</refname><refpurpose>How to run and debug your GLib application</refpurpose></refnamediv><refsect1><title>Running and debugging GLib Applications</title><refsect2><title>Environment variables</title><para> GLib inspects a few of environment variables in addition to standardvariables like <envar>LANG</envar>, <envar>PATH</envar> or <envar>HOME</envar>. </para><formalpara id="G_FILENAME_ENCODING">  <title><envar>G_FILENAME_ENCODING</envar></title>  <para>    This environment variable can be set to a comma-separated list of character    set names. GLib assumes that filenames are encoded in the first character     set from that list rather than in UTF-8. The special token "@locale" can be    used to specify the character set for the current locale.  </para></formalpara><formalpara id="G_BROKEN_FILENAMES">  <title><envar>G_BROKEN_FILENAMES</envar></title>  <para>    If this environment variable is set, GLib assumes that filenames are in     the locale encoding rather than in UTF-8. G_FILENAME_ENCODING takes    priority over G_BROKEN_FILENAMES.   </para></formalpara><formalpara id="G_MESSAGES_PREFIXED">  <title><envar>G_MESSAGES_PREFIXED</envar></title>  <para>    A list of log levels for which messages should be prefixed by the     program name and PID of the application. The default is to prefix    everything except <literal>G_LOG_LEVEL_MESSAGE</literal> and <literal>G_LOG_LEVEL_INFO</literal>.   </para></formalpara><formalpara id="G_DEBUG">  <title><envar>G_DEBUG</envar></title>  <para>    If GLib has been configured with <option>--enable-debug=yes</option>,    this variable can be set to a list of debug options, which cause GLib    to print out different types of debugging information.    <variablelist>      <varlistentry>        <term>fatal_warnings</term>        <listitem><para>Causes GLib to abort the program at the first call           to <link linkend="g-warning">g_warning</link>() or	   <link linkend="g-critical">g_critical</link>(). This option is            special in that it doesn't require GLib to be configured with            debugging support.</para>        </listitem>      </varlistentry>      <varlistentry>        <term>fatal_criticals</term>        <listitem><para>Causes GLib to abort the program at the first call           to <link linkend="g-critical">g_critical</link>(). This option is            special in that it doesn't require GLib to be configured with            debugging support.</para>        </listitem>      </varlistentry>      <varlistentry>        <term>gc-friendly</term>	<listitem>		<para>		  Newly allocated memory that isn't directly initialized, as well		  as memory being freed will be reset to 0. The point here is to		  allow memory checkers and similar programs that use bohem GC alike		  algorithms to produce more accurate results.		  This option is special in that it doesn't require GLib to be		  configured with debugging support.		</para>        </listitem>      </varlistentry>      <varlistentry>        <term>resident-modules</term>	<listitem>	  <para>	    All modules loaded by GModule will be made resident. This can be useful	    for tracking memory leaks in modules which are later unloaded; but it can	    also hide bugs where code is accessed after the module would have normally	    been unloaded.	    This option is special in that it doesn't require GLib to be 	    configured with debugging support.	  </para>        </listitem>      </varlistentry>      <varlistentry>        <term>bind-now-modules</term>	<listitem>	  <para>	    All modules loaded by GModule will bind their symbols at load time, even	    when the code uses %G_MODULE_BIND_LAZY.	    This option is special in that it doesn't require GLib to be 	    configured with debugging support.	  </para>        </listitem>      </varlistentry>    </variablelist>  </para></formalpara><formalpara id="G_SLICE">	<title><envar>G_SLICE</envar></title>	<para>	  This environment variable allows reconfiguration of the GSlice	  memory allocator.	  <variablelist>	    <varlistentry>	      <term>always-malloc</term>	      <listitem>		<para>		  This will cause all slices allocated through g_slice_alloc() and		  released by g_slice_free1() to be actually allocated via direct		  calls to g_malloc() and g_free().		  This is most useful for memory checkers and similar programs that		  use Bohem GC alike algorithms to produce more accurate results.		  It can also be in conjunction with debugging features of the system's		  malloc implementation such as glibc's MALLOC_CHECK_=2 to debug		  erroneous slice allocation code, allthough <literal>debug-blocks</literal>		  usually is a better suited debugging tool.		</para>	      </listitem>	    </varlistentry>	    <varlistentry>	      <term>debug-blocks</term>	      <listitem>		<para>		  Using this option (present since GLib-2.13) engages extra code		  which performs sanity checks on the released memory slices.		  Invalid slice adresses or slice sizes will be reported and lead to		  a program halt.		  This option is for debugging scenarios.		  In particular, client packages sporting their own test suite should		  <emphasis>always enable this option when running tests</emphasis>.		  Global slice validation is ensured by storing size and address information		  for each allocated chunk, and maintaining a global hash table of that data.		  That way, multi-thread scalability is given up, and memory consumption is		  increased. However, the resulting code usually performs acceptably well,		  possibly better than with comparable memory checking carried out using		  external tools. An example of a memory corruption scenario that cannot be		  reproduced with <literal>G_SLICE=always-malloc</literal>, but will be caught		  by <literal>G_SLICE=debug-blocks</literal> is as follows:		  <programlisting>		    void *slist = g_slist_alloc(); /* void* gives up type-safety */		    g_list_free (slist);           /* corruption: sizeof (GSList) != sizeof (GList) */		  </programlisting>		</para>	      </listitem>	    </varlistentry>	  </variablelist>	</para></formalpara><formalpara id="G_RANDOM_VERSION">  <title><envar>G_RANDOM_VERSION</envar></title>  <para>    If this environment variable is set to '2.0', the outdated    pseudo-random number seeding and generation algorithms from    GLib-2.0 are used instead of the new better ones. Use the GLib-2.0    algorithms only if you have sequences of numbers generated with    Glib-2.0 that you need to reproduce exactly.    </para></formalpara> <formalpara id="LIBCHARSET_ALIAS_DIR">  <title><envar>LIBCHARSET_ALIAS_DIR</envar></title>  <para>    Allows to specify a nonstandard location for the     <filename>charset.aliases</filename> file that is used by the    character set conversion routines. The default location is the     <replaceable>libdir</replaceable> specified at compilation time.  </para></formalpara> </refsect2><refsect2 id="setlocale"><title>Locale</title><para>A number of interfaces in GLib depend on the current locale in whichan application is running. Therefore, most GLib-using applications shouldcall <function>setlocale (LC_ALL, "")</function> to set up the current locale.</para><para>On Windows, in a C program there are several locale conceptsthat not necessarily are synchronized. On one hand, there is thesystem default ANSI code-page, which determines what encoding is usedfor file names handled by the C library's functions and the Win32API. (We are talking about the "narrow" functions here that takecharacter pointers, not the "wide" ones.)</para><para>On the other hand, there is the C library's current locale. Thecharacter set (code-page) used by that is not necessarily the same asthe system default ANSI code-page. Strings in this character set arereturned by functions like <function>strftime()</function>.</para></refsect2><refsect2><title>Traps and traces</title><para><indexterm><primary>g_trap_free_size</primary></indexterm><indexterm><primary>g_trap_realloc_size</primary></indexterm><indexterm><primary>g_trap_malloc_size</primary></indexterm>Some code portions contain trap variables that can be set during debugging time if GLib has been configured with <option>--enable-debug=yes</option>. Such traps lead to immediate code halts to examine the current program state and backtrace.</para><para>Currently, the following trap variables exist:<programlisting>static volatile gulong g_trap_free_size;static volatile gulong g_trap_realloc_size;static volatile gulong g_trap_malloc_size;</programlisting>If set to a size > 0, <link linkend="g-free">g_free</link>(), <link linkend="g-realloc">g_realloc</link>() and <link linkend="g-malloc">g_malloc</link>() will be intercepted if the size matches the size of the corresponding memory block. This will only work with <literal>g_mem_set_vtable (glib_mem_profiler_table)</literal> upon startup though, because memory profiling is required to match on the memory block sizes.</para><para>Note that many modern debuggers support conditional breakpoints, which achievepretty much the same. E.g. in gdb, you can do<programlisting>break g_malloccondition 1 n_bytes == 20</programlisting>to break only on g_malloc() calls where the size of the allocated memory blockis 20. </para></refsect2><refsect2><title>Memory statistics</title><para>g_mem_profile() will output a summary g_malloc() memory usage, if memoryprofiling has been enabled by calling <literal>g_mem_set_vtable (glib_mem_profiler_table)</literal> upon startup.</para><para>If GLib has been configured with <option>--enable-debug=yes</option>,then g_slice_debug_tree_statistics() can be called in a debugger to output details about the memory usage of the slice allocator.</para></refsect2></refsect1></refentry>