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<h2><span class="refentrytitle">Common Questions</span></h2>
<p>Common Questions —
Find answers to common questions in the GTK+ manual
</p>
</td>
<td class="gallery_image" valign="top" align="right"></td>
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<div class="refsect1">
<a name="id-1.2.5.3"></a><h2>Questions and Answers</h2>
<p>
This is an "index" of the reference manual organized by common "How do
I..." questions. If you aren't sure which documentation to read for
the question you have, this list is a good place to start.
</p>
<div class="qandaset">
<a name="id-1.2.5.3.3"></a><table border="0" style="width: 100%;">
<colgroup>
<col align="left" width="1%">
<col>
</colgroup>
<tbody>
<tr class="qandadiv"><td align="left" valign="top" colspan="2"><h5 class="title">
<a name="id-1.2.5.3.3.1"></a>1. General</h5></td></tr>
<tr class="question">
<td align="left" valign="top">
<a name="id-1.2.5.3.3.1.2"></a><a name="id-1.2.5.3.3.1.2.1"></a><p><b>1.1.</b></p>
</td>
<td align="left" valign="top"><p>
How do I get started with GTK+?
</p></td>
</tr>
<tr class="answer">
<td align="left" valign="top"></td>
<td align="left" valign="top"><p>
The GTK+ <a class="ulink" href="https://www.gtk.org" target="_top">website</a> offers some
<a class="ulink" href="https://www.gtk.org/documentation.php" target="_top">tutorials</a> and other
documentation (most of it about GTK+ 2.x, but mostly still applicable).
More documentation ranging from whitepapers to online books can be found at
the <a class="ulink" href="https://developer.gnome.org" target="_top">GNOME developer's site</a>.
After studying these materials you should be well prepared to come back to
this reference manual for details.
</p></td>
</tr>
<tr class="question">
<td align="left" valign="top">
<a name="id-1.2.5.3.3.1.3"></a><a name="id-1.2.5.3.3.1.3.1"></a><p><b>1.2.</b></p>
</td>
<td align="left" valign="top"><p>
Where can I get help with GTK+, submit a bug report, or make a feature
request?
</p></td>
</tr>
<tr class="answer">
<td align="left" valign="top"></td>
<td align="left" valign="top"><p>
See the <a class="link" href="gtk-resources.html" title="Mailing lists and bug reports">documentation on this topic</a>.
</p></td>
</tr>
<tr class="question">
<td align="left" valign="top">
<a name="id-1.2.5.3.3.1.4"></a><a name="id-1.2.5.3.3.1.4.1"></a><p><b>1.3.</b></p>
</td>
<td align="left" valign="top"><p>How do I port from one GTK+
version to another?</p></td>
</tr>
<tr class="answer">
<td align="left" valign="top"></td>
<td align="left" valign="top">
<p>
See <a class="xref" href="gtk-migrating-2-to-3.html" title="Migrating from GTK+ 2.x to GTK+ 3"><i>Migrating from GTK+ 2.x to GTK+ 3</i></a>.
You may also find useful information in the documentation for
specific widgets and functions.
</p>
<p>
If you have a question not covered in the manual, feel free to
ask on the mailing lists and please <a class="ulink" href="https://bugzilla.gnome.org" target="_top">file a bug report</a> against the
documentation.
</p>
</td>
</tr>
<tr class="question">
<td align="left" valign="top">
<a name="id-1.2.5.3.3.1.5"></a><a name="id-1.2.5.3.3.1.5.1"></a><p><b>1.4.</b></p>
</td>
<td align="left" valign="top"><p>
How does memory management work in GTK+? Should I free data returned
from functions?
</p></td>
</tr>
<tr class="answer">
<td align="left" valign="top"></td>
<td align="left" valign="top">
<p>
See the documentation for <span class="type">GObject</span> and <span class="type">GInitiallyUnowned</span>. For <span class="type">GObject</span> note
specifically <code class="function">g_object_ref()</code> and <code class="function">g_object_unref()</code>. <span class="type">GInitiallyUnowned</span> is a
subclass of <span class="type">GObject</span> so the same points apply, except that it has a "floating"
state (explained in its documentation).
</p>
<p>
For strings returned from functions, they will be declared "const"
if they should not be freed. Non-const strings should be
freed with <code class="function">g_free()</code>. Arrays follow the same rule. If you find an
undocumented exception to the rules, please report a bug to <a class="ulink" href="https://bugzilla.gnome.org" target="_top">https://bugzilla.gnome.org</a>.
</p>
</td>
</tr>
<tr class="question">
<td align="left" valign="top">
<a name="id-1.2.5.3.3.1.6"></a><a name="id-1.2.5.3.3.1.6.1"></a><p><b>1.5.</b></p>
</td>
<td align="left" valign="top"><p>
Why does my program leak memory, if I destroy a widget immediately
after creating it ?
</p></td>
</tr>
<tr class="answer">
<td align="left" valign="top"></td>
<td align="left" valign="top">
<p>
If <span class="structname">GtkFoo</span> isn't a toplevel window, then
</p>
<div class="informalexample">
<table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
<tbody>
<tr>
<td class="listing_lines" align="right"><pre>1
2</pre></td>
<td class="listing_code"><pre class="programlisting"><span class="normal">foo </span><span class="symbol">=</span><span class="normal"> </span><span class="function">gtk_foo_new</span><span class="normal"> </span><span class="symbol">();</span>
<span class="function"><a href="GtkWidget.html#gtk-widget-destroy">gtk_widget_destroy</a></span><span class="normal"> </span><span class="symbol">(</span><span class="normal">foo</span><span class="symbol">);</span></pre></td>
</tr>
</tbody>
</table>
</div>
<p>
is a memory leak, because no one assumed the initial floating
reference. If you are using a widget and you aren't immediately
packing it into a container, then you probably want standard
reference counting, not floating reference counting.
</p>
<p>
To get this, you must acquire a reference to the widget and drop the
floating reference (<span class="quote">“<span class="quote">ref and sink</span>”</span> in GTK+ parlance) after
creating it:
</p>
<div class="informalexample">
<table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
<tbody>
<tr>
<td class="listing_lines" align="right"><pre>1
2</pre></td>
<td class="listing_code"><pre class="programlisting"><span class="normal">foo </span><span class="symbol">=</span><span class="normal"> </span><span class="function">gtk_foo_new</span><span class="normal"> </span><span class="symbol">();</span>
<span class="function">g_object_ref_sink</span><span class="normal"> </span><span class="symbol">(</span><span class="normal">foo</span><span class="symbol">);</span></pre></td>
</tr>
</tbody>
</table>
</div>
<p>
When you want to get rid of the widget, you must call <a class="link" href="GtkWidget.html#gtk-widget-destroy" title="gtk_widget_destroy ()"><code class="function">gtk_widget_destroy()</code></a>
to break any external connections to the widget before dropping your
reference:
</p>
<div class="informalexample">
<table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
<tbody>
<tr>
<td class="listing_lines" align="right"><pre>1
2</pre></td>
<td class="listing_code"><pre class="programlisting"><span class="function"><a href="GtkWidget.html#gtk-widget-destroy">gtk_widget_destroy</a></span><span class="normal"> </span><span class="symbol">(</span><span class="normal">foo</span><span class="symbol">);</span>
<span class="function">g_object_unref</span><span class="normal"> </span><span class="symbol">(</span><span class="normal">foo</span><span class="symbol">);</span></pre></td>
</tr>
</tbody>
</table>
</div>
<p>
When you immediately add a widget to a container, it takes care of
assuming the initial floating reference and you don't have to worry
about reference counting at all ... just call <a class="link" href="GtkWidget.html#gtk-widget-destroy" title="gtk_widget_destroy ()"><code class="function">gtk_widget_destroy()</code></a>
to get rid of the widget.
</p>
</td>
</tr>
<tr class="question">
<td align="left" valign="top">
<a name="id-1.2.5.3.3.1.7"></a><a name="id-1.2.5.3.3.1.7.1"></a><p><b>1.6.</b></p>
</td>
<td align="left" valign="top"><p>
How do I use GTK+ with threads?
</p></td>
</tr>
<tr class="answer">
<td align="left" valign="top"></td>
<td align="left" valign="top"><p>
This is covered in the <GTKDOCLINK HREF="gdk-Threads">GDK threads
documentation</GTKDOCLINK>. See also the GThread
documentation for portable threading primitives.
</p></td>
</tr>
<tr class="question">
<td align="left" valign="top">
<a name="id-1.2.5.3.3.1.8"></a><a name="id-1.2.5.3.3.1.8.1"></a><p><b>1.7.</b></p>
</td>
<td align="left" valign="top"><p>
How do I internationalize a GTK+ program?
</p></td>
</tr>
<tr class="answer">
<td align="left" valign="top"></td>
<td align="left" valign="top">
<p>
Most people use <a class="ulink" href="https://www.gnu.org/software/gettext/" target="_top">GNU
gettext</a>, already required in order to install GLib. On a UNIX
or Linux system with gettext installed, type <code class="literal">info gettext</code>
to read the documentation.
</p>
<p>
The short checklist on how to use gettext is: call <code class="literal">bindtextdomain()</code> so
gettext can find the files containing your translations, call <code class="function">textdomain()</code>
to set the default translation domain, call <code class="literal">bind_textdomain_codeset()</code> to
request that all translated strings are returned in UTF-8, then call
<code class="function">gettext()</code> to look up each string to be translated in the default domain.
</p>
<p>
<code class="filename">gi18n.h</code> provides the following shorthand macros for
convenience.
Conventionally, people define macros as follows for convenience:
</p>
<div class="informalexample">
<table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
<tbody>
<tr>
<td class="listing_lines" align="right"><pre>1
2
3</pre></td>
<td class="listing_code"><pre class="programlisting"><span class="preproc">#define</span><span class="normal"> </span><span class="function">_</span><span class="symbol">(</span><span class="normal">x</span><span class="symbol">)</span><span class="normal"> </span><span class="function">gettext</span><span class="normal"> </span><span class="symbol">(</span><span class="normal">x</span><span class="symbol">)</span>
<span class="preproc">#define</span><span class="normal"> </span><span class="function">N_</span><span class="symbol">(</span><span class="normal">x</span><span class="symbol">)</span><span class="normal"> x</span>
<span class="preproc">#define</span><span class="normal"> </span><span class="function">C_</span><span class="symbol">(</span><span class="normal">ctx</span><span class="symbol">,</span><span class="normal">x</span><span class="symbol">)</span><span class="normal"> </span><span class="function">pgettext</span><span class="normal"> </span><span class="symbol">(</span><span class="normal">ctx</span><span class="symbol">,</span><span class="normal"> x</span><span class="symbol">)</span></pre></td>
</tr>
</tbody>
</table>
</div>
<p>
You use <code class="function">N_()</code> (N stands for no-op) to mark a string for translation in
a location where a function call to <code class="function">gettext()</code> is not allowed, such as
in an array initializer.
You eventually have to call <code class="function">gettext()</code> on the string to actually fetch
the translation. <code class="function">_()</code> both marks the string for translation and actually
translates it.
The <code class="function">C_()</code> macro (C stands for context) adds an additional context to
the string that is marked for translation, which can help to disambiguate
short strings that might need different translations in different
parts of your program.
</p>
<p>
Code using these macros ends up looking like this:
</p>
<div class="informalexample">
<table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
<tbody>
<tr>
<td class="listing_lines" align="right"><pre>1
2
3
4
5
6
7
8
9
10
11
12
13</pre></td>
<td class="listing_code"><pre class="programlisting"><span class="preproc">#include</span><span class="normal"> </span><span class="string"><gi18n.h></span>
<span class="keyword">static</span><span class="normal"> </span><span class="keyword">const</span><span class="normal"> </span><span class="type">char</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">global_variable </span><span class="symbol">=</span><span class="normal"> </span><span class="function">N_</span><span class="symbol">(</span><span class="string">"Translate this string"</span><span class="symbol">);</span>
<span class="keyword">static</span><span class="normal"> </span><span class="type">void</span>
<span class="function">make_widgets</span><span class="normal"> </span><span class="symbol">(</span><span class="type">void</span><span class="symbol">)</span>
<span class="cbracket">{</span>
<span class="normal"> </span><span class="usertype">GtkWidget</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">label1</span><span class="symbol">;</span>
<span class="normal"> </span><span class="usertype">GtkWidget</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">label2</span><span class="symbol">;</span>
<span class="normal"> label1 </span><span class="symbol">=</span><span class="normal"> </span><span class="function"><a href="GtkLabel.html#gtk-label-new">gtk_label_new</a></span><span class="normal"> </span><span class="symbol">(</span><span class="function">_</span><span class="symbol">(</span><span class="string">"Another string to translate"</span><span class="symbol">));</span>
<span class="normal"> label2 </span><span class="symbol">=</span><span class="normal"> </span><span class="function"><a href="GtkLabel.html#gtk-label-new">gtk_label_new</a></span><span class="normal"> </span><span class="symbol">(</span><span class="function">_</span><span class="symbol">(</span><span class="normal">global_variable</span><span class="symbol">));</span>
<span class="symbol">...</span></pre></td>
</tr>
</tbody>
</table>
</div>
<p>
</p>
<p>
Libraries using gettext should use <code class="function">dgettext()</code> instead of <code class="function">gettext()</code>, which
allows them to specify the translation domain each time they ask for a
translation. Libraries should also avoid calling <code class="function">textdomain()</code>, since
they will be specifying the domain instead of using the default.
</p>
<p>
With the convention that the macro <code class="literal">GETTEXT_PACKAGE</code> is
defined to hold your libraries translation domain,
<code class="filename">gi18n-lib.h</code> can be included to provide
the following convenience:
</p>
<div class="informalexample">
<table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
<tbody>
<tr>
<td class="listing_lines" align="right"><pre>1</pre></td>
<td class="listing_code"><pre class="programlisting"><span class="preproc">#define</span><span class="normal"> </span><span class="function">_</span><span class="symbol">(</span><span class="normal">x</span><span class="symbol">)</span><span class="normal"> </span><span class="function">dgettext</span><span class="normal"> </span><span class="symbol">(</span><span class="normal">GETTEXT_PACKAGE</span><span class="symbol">,</span><span class="normal"> x</span><span class="symbol">)</span></pre></td>
</tr>
</tbody>
</table>
</div>
<p>
</p>
</td>
</tr>
<tr class="question">
<td align="left" valign="top">
<a name="id-1.2.5.3.3.1.9"></a><a name="id-1.2.5.3.3.1.9.1"></a><p><b>1.8.</b></p>
</td>
<td align="left" valign="top"><p>
How do I use non-ASCII characters in GTK+ programs ?
</p></td>
</tr>
<tr class="answer">
<td align="left" valign="top"></td>
<td align="left" valign="top">
<p>
GTK+ uses <a class="ulink" href="http://www.unicode.org" target="_top">Unicode</a> (more exactly
UTF-8) for all text. UTF-8 encodes each Unicode codepoint as a sequence of
one to six bytes and has a number of nice properties which make it a good
choice for working with Unicode text in C programs:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem"><p>
ASCII characters are encoded by their familiar ASCII codepoints.
</p></li>
<li class="listitem"><p>
ASCII characters never appear as part of any other character.
</p></li>
<li class="listitem"><p>
The zero byte doesn't occur as part of a character, so that UTF-8 strings
can be manipulated with the usual C library functions for handling
zero-terminated strings.
</p></li>
</ul></div>
<p>
More information about Unicode and UTF-8 can be found in the
<a class="ulink" href="https://www.cl.cam.ac.uk/~mgk25/unicode.html" target="_top">UTF-8 and Unicode
FAQ for Unix/Linux</a>.
GLib provides functions for converting strings between UTF-8 and other
encodings, see <code class="function">g_locale_to_utf8()</code> and <code class="function">g_convert()</code>.
</p>
<p>
Text coming from external sources (e.g. files or user input), has to be
converted to UTF-8 before being handed over to GTK+. The following example
writes the content of a IS0-8859-1 encoded text file to
<code class="literal">stdout</code>:
</p>
<div class="informalexample">
<table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
<tbody>
<tr>
<td class="listing_lines" align="right"><pre>1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18</pre></td>
<td class="listing_code"><pre class="programlisting"><span class="usertype">gchar</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">text</span><span class="symbol">,</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">utf8_text</span><span class="symbol">;</span>
<span class="usertype">gsize</span><span class="normal"> length</span><span class="symbol">;</span>
<span class="usertype">GError</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">error </span><span class="symbol">=</span><span class="normal"> NULL</span><span class="symbol">;</span>
<span class="keyword">if</span><span class="normal"> </span><span class="symbol">(</span><span class="function">g_file_get_contents</span><span class="normal"> </span><span class="symbol">(</span><span class="normal">filename</span><span class="symbol">,</span><span class="normal"> </span><span class="symbol">&</span><span class="normal">text</span><span class="symbol">,</span><span class="normal"> </span><span class="symbol">&</span><span class="normal">length</span><span class="symbol">,</span><span class="normal"> NULL</span><span class="symbol">))</span>
<span class="normal"> </span><span class="cbracket">{</span>
<span class="normal"> utf8_text </span><span class="symbol">=</span><span class="normal"> </span><span class="function">g_convert</span><span class="normal"> </span><span class="symbol">(</span><span class="normal">text</span><span class="symbol">,</span><span class="normal"> length</span><span class="symbol">,</span><span class="normal"> </span><span class="string">"UTF-8"</span><span class="symbol">,</span><span class="normal"> </span><span class="string">"ISO-8859-1"</span><span class="symbol">,</span>
<span class="normal"> NULL</span><span class="symbol">,</span><span class="normal"> NULL</span><span class="symbol">,</span><span class="normal"> </span><span class="symbol">&</span><span class="normal">error</span><span class="symbol">);</span>
<span class="normal"> </span><span class="keyword">if</span><span class="normal"> </span><span class="symbol">(</span><span class="normal">error </span><span class="symbol">!=</span><span class="normal"> NULL</span><span class="symbol">)</span>
<span class="normal"> </span><span class="cbracket">{</span>
<span class="normal"> </span><span class="function">fprintf</span><span class="normal"> </span><span class="symbol">(</span><span class="string">"Couldn't convert file %s to UTF-8</span><span class="specialchar">\n</span><span class="string">"</span><span class="symbol">,</span><span class="normal"> filename</span><span class="symbol">);</span>
<span class="normal"> </span><span class="function">g_error_free</span><span class="normal"> </span><span class="symbol">(</span><span class="normal">error</span><span class="symbol">);</span>
<span class="normal"> </span><span class="cbracket">}</span>
<span class="normal"> </span><span class="keyword">else</span>
<span class="normal"> </span><span class="function">g_print</span><span class="normal"> </span><span class="symbol">(</span><span class="normal">utf8_text</span><span class="symbol">);</span>
<span class="normal"> </span><span class="cbracket">}</span>
<span class="keyword">else</span>
<span class="normal"> </span><span class="function">fprintf</span><span class="normal"> </span><span class="symbol">(</span><span class="normal">stderr</span><span class="symbol">,</span><span class="normal"> </span><span class="string">"Unable to read file %s</span><span class="specialchar">\n</span><span class="string">"</span><span class="symbol">,</span><span class="normal"> filename</span><span class="symbol">);</span></pre></td>
</tr>
</tbody>
</table>
</div>
<p>
</p>
<p>
For string literals in the source code, there are several alternatives for
handling non-ASCII content:
</p>
<div class="variablelist"><table border="0" class="variablelist">
<colgroup>
<col align="left" valign="top">
<col>
</colgroup>
<tbody>
<tr>
<td><p><span class="term">direct UTF-8</span></p></td>
<td><p>
If your editor and compiler are capable of handling UTF-8 encoded sources,
it is very convenient to simply use UTF-8 for string literals, since it
allows you to edit the strings in "wysiwyg". Note that choosing this option
may reduce the portability of your code.
</p></td>
</tr>
<tr>
<td><p><span class="term">escaped UTF-8</span></p></td>
<td><p>
Even if your toolchain can't handle UTF-8 directly, you can still encode
string literals in UTF-8 by using octal or hexadecimal escapes like
<code class="literal">\212</code> or <code class="literal">\xa8</code> to encode each byte.
This is portable, but modifying the escaped strings is not very convenient.
Be careful when mixing hexadecimal escapes with ordinary text;
<code class="literal">"\xa8abcd"</code> is a string of length 1 !
</p></td>
</tr>
<tr>
<td><p><span class="term">runtime conversion</span></p></td>
<td><p>
If the string literals can be represented in an encoding which your
toolchain can handle (e.g. IS0-8859-1), you can write your source files
in that encoding and use <code class="function">g_convert()</code> to convert the strings to UTF-8 at
runtime. Note that this has some runtime overhead, so you may want to move
the conversion out of inner loops.
</p></td>
</tr>
</tbody>
</table></div>
<p>
Here is an example showing the three approaches using the copyright sign
© which has Unicode and ISO-8859-1 codepoint 169 and is represented
in UTF-8 by the two bytes 194, 169, or <code class="literal">"\302\251"</code> as
a string literal:
</p>
<div class="informalexample">
<table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
<tbody>
<tr>
<td class="listing_lines" align="right"><pre>1
2
3
4
5</pre></td>
<td class="listing_code"><pre class="programlisting"><span class="function">g_print</span><span class="normal"> </span><span class="symbol">(</span><span class="string">"direct UTF-8: ©"</span><span class="symbol">);</span>
<span class="function">g_print</span><span class="normal"> </span><span class="symbol">(</span><span class="string">"escaped UTF-8: </span><span class="specialchar">\3</span><span class="string">02</span><span class="specialchar">\2</span><span class="string">51"</span><span class="symbol">);</span>
<span class="normal">text </span><span class="symbol">=</span><span class="normal"> </span><span class="function">g_convert</span><span class="normal"> </span><span class="symbol">(</span><span class="string">"runtime conversion: ©"</span><span class="symbol">,</span><span class="normal"> </span><span class="symbol">-</span><span class="number">1</span><span class="symbol">,</span><span class="normal"> </span><span class="string">"ISO-8859-1"</span><span class="symbol">,</span><span class="normal"> </span><span class="string">"UTF-8"</span><span class="symbol">,</span><span class="normal"> NULL</span><span class="symbol">,</span><span class="normal"> NULL</span><span class="symbol">,</span><span class="normal"> NULL</span><span class="symbol">);</span>
<span class="function">g_print</span><span class="symbol">(</span><span class="normal">text</span><span class="symbol">);</span>
<span class="function">g_free</span><span class="normal"> </span><span class="symbol">(</span><span class="normal">text</span><span class="symbol">);</span></pre></td>
</tr>
</tbody>
</table>
</div>
<p>
</p>
<p>
If you are using <code class="function">gettext()</code> to localize your application, you need to
call <code class="literal">bind_textdomain_codeset()</code> to ensure that translated strings are
returned in UTF-8 encoding.
</p>
</td>
</tr>
<tr class="question">
<td align="left" valign="top">
<a name="id-1.2.5.3.3.1.10"></a><a name="id-1.2.5.3.3.1.10.1"></a><p><b>1.9.</b></p>
</td>
<td align="left" valign="top"><p>
How do I use GTK+ with C++?
</p></td>
</tr>
<tr class="answer">
<td align="left" valign="top"></td>
<td align="left" valign="top">
<p>
There are two ways to approach this. The GTK+ header files use the subset
of C that's also valid C++, so you can simply use the normal GTK+ API
in a C++ program. Alternatively, you can use a "C++ binding"
such as <a class="ulink" href="https://www.gtkmm.org/" target="_top">gtkmm</a>
which provides a native C++ API.
</p>
<p>
When using GTK+ directly, keep in mind that only functions can be
connected to signals, not methods. So you will need to use global
functions or "static" class functions for signal connections.
</p>
<p>
Another common issue when using GTK+ directly is that
C++ will not implicitly convert an integer to an enumeration.
This comes up when using bitfields; in C you can write the following
code:
</p>
<div class="informalexample">
<table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
<tbody>
<tr>
<td class="listing_lines" align="right"><pre>1
2</pre></td>
<td class="listing_code"><pre class="programlisting"><span class="function"><a href="../html/gdk3-Windows.html#gdk-window-set-events">gdk_window_set_events</a></span><span class="normal"> </span><span class="symbol">(</span><span class="normal">gdk_window</span><span class="symbol">,</span>
<span class="normal"> <a href="../html/gdk3-Events.html#GDK-BUTTON-PRESS-MASK:CAPS">GDK_BUTTON_PRESS_MASK</a> </span><span class="symbol">|</span><span class="normal"> <a href="../html/gdk3-Events.html#GDK-BUTTON-RELEASE-MASK:CAPS">GDK_BUTTON_RELEASE_MASK</a></span><span class="symbol">);</span></pre></td>
</tr>
</tbody>
</table>
</div>
<p>
while in C++ you must write:
</p>
<div class="informalexample">
<table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
<tbody>
<tr>
<td class="listing_lines" align="right"><pre>1
2</pre></td>
<td class="listing_code"><pre class="programlisting"><span class="function"><a href="../html/gdk3-Windows.html#gdk-window-set-events">gdk_window_set_events</a></span><span class="normal"> </span><span class="symbol">(</span><span class="normal">gdk_window</span><span class="symbol">,</span>
<span class="normal"> </span><span class="symbol">(</span><span class="normal"><a href="../html/gdk3-Events.html#GdkEventMask">GdkEventMask</a></span><span class="symbol">)</span><span class="normal"> <a href="../html/gdk3-Events.html#GDK-BUTTON-PRESS-MASK:CAPS">GDK_BUTTON_PRESS_MASK</a> </span><span class="symbol">|</span><span class="normal"> <a href="../html/gdk3-Events.html#GDK-BUTTON-RELEASE-MASK:CAPS">GDK_BUTTON_RELEASE_MASK</a></span><span class="symbol">);</span></pre></td>
</tr>
</tbody>
</table>
</div>
<p>
There are very few functions that require this cast, however.
</p>
</td>
</tr>
<tr class="question">
<td align="left" valign="top">
<a name="id-1.2.5.3.3.1.11"></a><a name="id-1.2.5.3.3.1.11.1"></a><p><b>1.10.</b></p>
</td>
<td align="left" valign="top"><p>
How do I use GTK+ with other non-C languages?
</p></td>
</tr>
<tr class="answer">
<td align="left" valign="top"></td>
<td align="left" valign="top"><p>
See the <a class="ulink" href="https://www.gtk.org/language-bindings.php" target="_top">list of language
bindings</a> on <a class="ulink" href="https://www.gtk.org" target="_top">https://www.gtk.org</a>.
</p></td>
</tr>
<tr class="question">
<td align="left" valign="top">
<a name="id-1.2.5.3.3.1.12"></a><a name="id-1.2.5.3.3.1.12.1"></a><p><b>1.11.</b></p>
</td>
<td align="left" valign="top"><p>
How do I load an image or animation from a file?
</p></td>
</tr>
<tr class="answer">
<td align="left" valign="top"></td>
<td align="left" valign="top">
<p>
To load an image file straight into a display widget, use
<a class="link" href="GtkImage.html#gtk-image-new-from-file" title="gtk_image_new_from_file ()"><code class="function">gtk_image_new_from_file()</code></a> <a href="#ftn.id-1.2.5.3.3.1.12.2.1.2" class="footnote" name="id-1.2.5.3.3.1.12.2.1.2"><sup class="footnote">[1]</sup></a>.
To load an image for another purpose, use <code class="function">gdk_pixbuf_new_from_file()</code>. To
load an animation, use <code class="function">gdk_pixbuf_animation_new_from_file()</code>.
<code class="function">gdk_pixbuf_animation_new_from_file()</code> can also load non-animated images, so
use it in combination with <code class="function">gdk_pixbuf_animation_is_static_image()</code> to load a
file of unknown type.
</p>
<p>
To load an image or animation file asynchronously (without blocking), use
<span class="type">GdkPixbufLoader</span>.
</p>
</td>
</tr>
<tr class="question">
<td align="left" valign="top">
<a name="id-1.2.5.3.3.1.13"></a><a name="id-1.2.5.3.3.1.13.1"></a><p><b>1.12.</b></p>
</td>
<td align="left" valign="top"><p>
How do I draw text ?
</p></td>
</tr>
<tr class="answer">
<td align="left" valign="top"></td>
<td align="left" valign="top">
<p>
To draw a piece of text, use a Pango layout and <code class="function">pango_cairo_show_layout()</code>.
</p>
<div class="informalexample">
<table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
<tbody>
<tr>
<td class="listing_lines" align="right"><pre>1
2
3
4
5
6</pre></td>
<td class="listing_code"><pre class="programlisting"><span class="normal">layout </span><span class="symbol">=</span><span class="normal"> </span><span class="function"><a href="GtkWidget.html#gtk-widget-create-pango-layout">gtk_widget_create_pango_layout</a></span><span class="normal"> </span><span class="symbol">(</span><span class="normal">widget</span><span class="symbol">,</span><span class="normal"> text</span><span class="symbol">);</span>
<span class="normal">fontdesc </span><span class="symbol">=</span><span class="normal"> </span><span class="function">pango_font_description_from_string</span><span class="normal"> </span><span class="symbol">(</span><span class="string">"Luxi Mono 12"</span><span class="symbol">);</span>
<span class="function">pango_layout_set_font_description</span><span class="normal"> </span><span class="symbol">(</span><span class="normal">layout</span><span class="symbol">,</span><span class="normal"> fontdesc</span><span class="symbol">);</span>
<span class="function">pango_cairo_show_layout</span><span class="normal"> </span><span class="symbol">(</span><span class="normal">cr</span><span class="symbol">,</span><span class="normal"> layout</span><span class="symbol">);</span>
<span class="function">pango_font_description_free</span><span class="normal"> </span><span class="symbol">(</span><span class="normal">fontdesc</span><span class="symbol">);</span>
<span class="function">g_object_unref</span><span class="normal"> </span><span class="symbol">(</span><span class="normal">layout</span><span class="symbol">);</span></pre></td>
</tr>
</tbody>
</table>
</div>
<p>
</p>
<p>
See also the
<a class="ulink" href="https://developer.gnome.org/pango/stable/pango-Cairo-Rendering.html" target="_top">Cairo Rendering</a>
section of <a class="ulink" href="https://developer.gnome.org/pango/stable/" target="_top">Pango manual</a>.
</p>
</td>
</tr>
<tr class="question">
<td align="left" valign="top">
<a name="id-1.2.5.3.3.1.14"></a><a name="id-1.2.5.3.3.1.14.1"></a><p><b>1.13.</b></p>
</td>
<td align="left" valign="top"><p>
How do I measure the size of a piece of text ?
</p></td>
</tr>
<tr class="answer">
<td align="left" valign="top"></td>
<td align="left" valign="top">
<p>
To obtain the size of a piece of text, use a Pango layout and
<code class="function">pango_layout_get_pixel_size()</code>, using code like the following:
</p>
<div class="informalexample">
<table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
<tbody>
<tr>
<td class="listing_lines" align="right"><pre>1
2
3
4
5
6</pre></td>
<td class="listing_code"><pre class="programlisting"><span class="normal">layout </span><span class="symbol">=</span><span class="normal"> </span><span class="function"><a href="GtkWidget.html#gtk-widget-create-pango-layout">gtk_widget_create_pango_layout</a></span><span class="normal"> </span><span class="symbol">(</span><span class="normal">widget</span><span class="symbol">,</span><span class="normal"> text</span><span class="symbol">);</span>
<span class="normal">fontdesc </span><span class="symbol">=</span><span class="normal"> </span><span class="function">pango_font_description_from_string</span><span class="normal"> </span><span class="symbol">(</span><span class="string">"Luxi Mono 12"</span><span class="symbol">);</span>
<span class="function">pango_layout_set_font_description</span><span class="normal"> </span><span class="symbol">(</span><span class="normal">layout</span><span class="symbol">,</span><span class="normal"> fontdesc</span><span class="symbol">);</span>
<span class="function">pango_layout_get_pixel_size</span><span class="normal"> </span><span class="symbol">(</span><span class="normal">layout</span><span class="symbol">,</span><span class="normal"> </span><span class="symbol">&</span><span class="normal">width</span><span class="symbol">,</span><span class="normal"> </span><span class="symbol">&</span><span class="normal">height</span><span class="symbol">);</span>
<span class="function">pango_font_description_free</span><span class="normal"> </span><span class="symbol">(</span><span class="normal">fontdesc</span><span class="symbol">);</span>
<span class="function">g_object_unref</span><span class="normal"> </span><span class="symbol">(</span><span class="normal">layout</span><span class="symbol">);</span></pre></td>
</tr>
</tbody>
</table>
</div>
<p>
</p>
<p>
See also the
<a class="ulink" href="https://developer.gnome.org/pango/stable/pango-Layout-Objects.html" target="_top">Layout Objects</a>
section of <a class="ulink" href="https://developer.gnome.org/pango/stable/" target="_top">Pango manual</a>.
</p>
</td>
</tr>
<tr class="question">
<td align="left" valign="top">
<a name="id-1.2.5.3.3.1.15"></a><a name="id-1.2.5.3.3.1.15.1"></a><p><b>1.14.</b></p>
</td>
<td align="left" valign="top"><p>
Why are types not registered if I use their <code class="literal">GTK_TYPE_BLAH</code>
macro ?
</p></td>
</tr>
<tr class="answer">
<td align="left" valign="top"></td>
<td align="left" valign="top">
<p>
The <code class="literal">GTK_TYPE_BLAH</code> macros are defined as calls to
<code class="literal">gtk_blah_get_type()</code>, and the <code class="literal">_get_type()</code>
functions are declared as <code class="literal">G_GNUC_CONST</code> which allows the compiler to optimize
the call away if it appears that the value is not being used.
</p>
<p>
A common workaround for this problem is to store the result in a volatile
variable, which keeps the compiler from optimizing the call away.
</p>
<div class="informalexample">
<table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
<tbody>
<tr>
<td class="listing_lines" align="right"><pre>1</pre></td>
<td class="listing_code"><pre class="programlisting"><span class="keyword">volatile</span><span class="normal"> </span><span class="usertype">GType</span><span class="normal"> dummy </span><span class="symbol">=</span><span class="normal"> GTK_TYPE_BLAH</span><span class="symbol">;</span></pre></td>
</tr>
</tbody>
</table>
</div>
<p>
</p>
</td>
</tr>
<tr class="question">
<td align="left" valign="top">
<a name="id-1.2.5.3.3.1.16"></a><a name="id-1.2.5.3.3.1.16.1"></a><p><b>1.15.</b></p>
</td>
<td align="left" valign="top"><p>
How do I create a transparent toplevel window ?
</p></td>
</tr>
<tr class="answer">
<td align="left" valign="top"></td>
<td align="left" valign="top">
<p>
To make a window transparent, it needs to use a visual which supports that.
This is done by getting the RGBA visual of the screen with
<a href="../html/GdkScreen.html#gdk-screen-get-rgba-visual"><code class="function">gdk_screen_get_rgba_visual()</code></a> and setting it on the window. Note that
<a href="../html/GdkScreen.html#gdk-screen-get-rgba-visual"><code class="function">gdk_screen_get_rgba_visual()</code></a> will return <code class="literal">NULL</code> if transparent windows
are not supported on the screen, you should fall back to
<a href="../html/GdkScreen.html#gdk-screen-get-system-visual"><code class="function">gdk_screen_get_system_visual()</code></a> in that case. Additionally, note that this
will change from screen to screen, so it needs to be repeated whenever the
window is moved to a different screen.
</p>
<div class="informalexample">
<table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
<tbody>
<tr>
<td class="listing_lines" align="right"><pre>1
2
3
4
5
6
7</pre></td>
<td class="listing_code"><pre class="programlisting"><span class="usertype">GdkVisual</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">visual</span><span class="symbol">;</span>
<span class="normal">visual </span><span class="symbol">=</span><span class="normal"> </span><span class="function"><a href="../html/GdkScreen.html#gdk-screen-get-rgba-visual">gdk_screen_get_rgba_visual</a></span><span class="normal"> </span><span class="symbol">(</span><span class="normal">screen</span><span class="symbol">);</span>
<span class="keyword">if</span><span class="normal"> </span><span class="symbol">(</span><span class="normal">visual </span><span class="symbol">==</span><span class="normal"> NULL</span><span class="symbol">)</span>
<span class="normal"> visual </span><span class="symbol">=</span><span class="normal"> </span><span class="function"><a href="../html/GdkScreen.html#gdk-screen-get-system-visual">gdk_screen_get_system_visual</a></span><span class="normal"> </span><span class="symbol">(</span><span class="normal">screen</span><span class="symbol">);</span>
<span class="function"><a href="GtkWidget.html#gtk-widget-set-visual">gtk_widget_set_visual</a></span><span class="normal"> </span><span class="symbol">(</span><span class="function">GTK_WIDGET</span><span class="normal"> </span><span class="symbol">(</span><span class="normal">window</span><span class="symbol">),</span><span class="normal"> visual</span><span class="symbol">);</span></pre></td>
</tr>
</tbody>
</table>
</div>
<p>
To fill the alpha channel on the window simply use cairos
RGBA drawing capabilities.
</p>
<p>
Note that the presence of an RGBA visual is no guarantee that the
window will actually appear transparent on screen. On X11, this
requires a compositing manager to be running. See
<a class="link" href="GtkWidget.html#gtk-widget-is-composited" title="gtk_widget_is_composited ()"><code class="function">gtk_widget_is_composited()</code></a> for a way to find out if the alpha
channel will be respected.
</p>
</td>
</tr>
<tr class="qandadiv"><td align="left" valign="top" colspan="2"><h5 class="title">
<a name="id-1.2.5.3.3.2"></a>2. Which widget should I use...</h5></td></tr>
<tr class="question">
<td align="left" valign="top">
<a name="id-1.2.5.3.3.2.2"></a><a name="id-1.2.5.3.3.2.2.1"></a><p><b>2.1.</b></p>
</td>
<td align="left" valign="top"><p>
...for lists and trees?
</p></td>
</tr>
<tr class="answer">
<td align="left" valign="top"></td>
<td align="left" valign="top"><p>
See <a class="link" href="TreeWidget.html" title="Tree and List Widget Overview">tree widget overview</a> — you
should use the <a class="link" href="GtkTreeView.html" title="GtkTreeView"><span class="type">GtkTreeView</span></a> widget. (A list is just a tree with no branches,
so the tree widget is used for lists as well).
</p></td>
</tr>
<tr class="question">
<td align="left" valign="top">
<a name="id-1.2.5.3.3.2.3"></a><a name="id-1.2.5.3.3.2.3.1"></a><p><b>2.2.</b></p>
</td>
<td align="left" valign="top"><p>
...for multi-line text display or editing?
</p></td>
</tr>
<tr class="answer">
<td align="left" valign="top"></td>
<td align="left" valign="top">
<p>
See <a class="link" href="TextWidget.html" title="Text Widget Overview">text widget overview</a> — you
should use the <a class="link" href="GtkTextView.html" title="GtkTextView"><span class="type">GtkTextView</span></a> widget.
</p>
<p>
If you only have a small amount of text, <a class="link" href="GtkLabel.html" title="GtkLabel"><span class="type">GtkLabel</span></a> may also be appropriate
of course. It can be made selectable with <a class="link" href="GtkLabel.html#gtk-label-set-selectable" title="gtk_label_set_selectable ()"><code class="function">gtk_label_set_selectable()</code></a>. For a
single-line text entry, see <a class="link" href="GtkEntry.html" title="GtkEntry"><span class="type">GtkEntry</span></a>.
</p>
</td>
</tr>
<tr class="question">
<td align="left" valign="top">
<a name="id-1.2.5.3.3.2.4"></a><a name="id-1.2.5.3.3.2.4.1"></a><p><b>2.3.</b></p>
</td>
<td align="left" valign="top"><p>
...to display an image or animation?
</p></td>
</tr>
<tr class="answer">
<td align="left" valign="top"></td>
<td align="left" valign="top"><p>
<a class="link" href="GtkImage.html" title="GtkImage"><span class="type">GtkImage</span></a> can display images in just about any format GTK+ understands.
You can also use <a class="link" href="GtkDrawingArea.html" title="GtkDrawingArea"><span class="type">GtkDrawingArea</span></a> if you need to do something more complex,
such as draw text or graphics over the top of the image.
</p></td>
</tr>
<tr class="question">
<td align="left" valign="top">
<a name="id-1.2.5.3.3.2.5"></a><a name="id-1.2.5.3.3.2.5.1"></a><p><b>2.4.</b></p>
</td>
<td align="left" valign="top"><p>
...for presenting a set of mutually-exclusive choices, where Windows
would use a combo box?
</p></td>
</tr>
<tr class="answer">
<td align="left" valign="top"></td>
<td align="left" valign="top"><p>
With GTK+, a <a class="link" href="GtkComboBox.html" title="GtkComboBox"><span class="type">GtkComboBox</span></a> is the recommended widget to use for this use case.
This widget looks like either a combo box or the current option menu, depending
on the current theme. If you need an editable text entry, use the
<a class="link" href="GtkComboBox.html#GtkComboBox--has-entry" title="The “has-entry” property"><span class="type">“has-entry”</span></a> property.
</p></td>
</tr>
<tr class="qandadiv"><td align="left" valign="top" colspan="2"><h5 class="title">
<a name="id-1.2.5.3.3.3"></a>3. GtkWidget</h5></td></tr>
<tr class="question">
<td align="left" valign="top">
<a name="id-1.2.5.3.3.3.2"></a><a name="id-1.2.5.3.3.3.2.1"></a><p><b>3.1.</b></p>
</td>
<td align="left" valign="top"><p>
How do I change the color of a widget?
</p></td>
</tr>
<tr class="answer">
<td align="left" valign="top"></td>
<td align="left" valign="top">
<p>
See <a class="link" href="GtkWidget.html#gtk-widget-override-color" title="gtk_widget_override_color ()"><code class="function">gtk_widget_override_color()</code></a> and <a class="link" href="GtkWidget.html#gtk-widget-override-background-color" title="gtk_widget_override_background_color ()"><code class="function">gtk_widget_override_background_color()</code></a>.
You can also change the appearance of a widget by installing a
custom style provider, see <a class="link" href="GtkStyleContext.html#gtk-style-context-add-provider" title="gtk_style_context_add_provider ()"><code class="function">gtk_style_context_add_provider()</code></a>.
</p>
<p>To change the background color for widgets such as <a class="link" href="GtkLabel.html" title="GtkLabel"><span class="type">GtkLabel</span></a> that
have no background, place them in a <a class="link" href="GtkEventBox.html" title="GtkEventBox"><span class="type">GtkEventBox</span></a> and set the background
of the event box.
</p>
</td>
</tr>
<tr class="question">
<td align="left" valign="top">
<a name="id-1.2.5.3.3.3.3"></a><a name="id-1.2.5.3.3.3.3.1"></a><p><b>3.2.</b></p>
</td>
<td align="left" valign="top"><p>
How do I change the font of a widget?
</p></td>
</tr>
<tr class="answer">
<td align="left" valign="top"></td>
<td align="left" valign="top">
<p>
This has several possible answers, depending on what exactly you want to
achieve. One option is <a class="link" href="GtkWidget.html#gtk-widget-override-font" title="gtk_widget_override_font ()"><code class="function">gtk_widget_override_font()</code></a>.
</p>
<div class="informalexample">
<table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
<tbody>
<tr>
<td class="listing_lines" align="right"><pre>1
2
3
4</pre></td>
<td class="listing_code"><pre class="programlisting"><span class="usertype">PangoFontDesc</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">font_desc </span><span class="symbol">=</span><span class="normal"> </span><span class="function">pango_font_description_new</span><span class="normal"> </span><span class="symbol">();</span>
<span class="function">pango_font_description_set_size</span><span class="normal"> </span><span class="symbol">(</span><span class="normal">font_desc</span><span class="symbol">,</span><span class="normal"> </span><span class="number">40</span><span class="symbol">);</span>
<span class="function"><a href="GtkWidget.html#gtk-widget-override-font">gtk_widget_override_font</a></span><span class="normal"> </span><span class="symbol">(</span><span class="normal">widget</span><span class="symbol">,</span><span class="normal"> font</span><span class="symbol">);</span>
<span class="function">pango_font_description_free</span><span class="normal"> </span><span class="symbol">(</span><span class="normal">font_desc</span><span class="symbol">);</span></pre></td>
</tr>
</tbody>
</table>
</div>
<p>
</p>
<p>
If you want to make the text of a label larger, you can use
<a class="link" href="GtkLabel.html#gtk-label-set-markup" title="gtk_label_set_markup ()"><code class="function">gtk_label_set_markup()</code></a>:
</p>
<div class="informalexample">
<table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
<tbody>
<tr>
<td class="listing_lines" align="right"><pre>1</pre></td>
<td class="listing_code"><pre class="programlisting"><span class="function"><a href="GtkLabel.html#gtk-label-set-markup">gtk_label_set_markup</a></span><span class="normal"> </span><span class="symbol">(</span><span class="normal">label</span><span class="symbol">,</span><span class="normal"> </span><span class="string">"<big>big text</big>"</span><span class="symbol">);</span></pre></td>
</tr>
</tbody>
</table>
</div>
<p>
This is preferred for many apps because it's a relative size to the
user's chosen font size. See <code class="function">g_markup_escape_text()</code> if you are
constructing such strings on the fly.
</p>
<p>
You can also change the font of a widget by putting
</p>
<pre class="programlisting">
.my-widget-class {
font: Sans 30;
}
</pre>
<p>
in a CSS file, loading it with <a class="link" href="GtkCssProvider.html#gtk-css-provider-load-from-file" title="gtk_css_provider_load_from_file ()"><code class="function">gtk_css_provider_load_from_file()</code></a>, and
adding the provider with <a class="link" href="GtkStyleContext.html#gtk-style-context-add-provider-for-screen" title="gtk_style_context_add_provider_for_screen ()"><code class="function">gtk_style_context_add_provider_for_screen()</code></a>.
To associate this style information with your widget, set a style class
on its <a class="link" href="GtkStyleContext.html" title="GtkStyleContext"><span class="type">GtkStyleContext</span></a> using <a class="link" href="GtkStyleContext.html#gtk-style-context-add-class" title="gtk_style_context_add_class ()"><code class="function">gtk_style_context_add_class()</code></a>.
The advantage of this approach is that users can then override the font
you have chosen. See the <a class="link" href="GtkStyleContext.html" title="GtkStyleContext"><span class="type">GtkStyleContext</span></a> documentation for more discussion.
</p>
</td>
</tr>
<tr class="question">
<td align="left" valign="top">
<a name="id-1.2.5.3.3.3.4"></a><a name="id-1.2.5.3.3.3.4.1"></a><p><b>3.3.</b></p>
</td>
<td align="left" valign="top"><p>
How do I disable/ghost/desensitize a widget?
</p></td>
</tr>
<tr class="answer">
<td align="left" valign="top"></td>
<td align="left" valign="top"><p>
In GTK+ a disabled widget is termed "insensitive."
See <a class="link" href="GtkWidget.html#gtk-widget-set-sensitive" title="gtk_widget_set_sensitive ()"><code class="function">gtk_widget_set_sensitive()</code></a>.
</p></td>
</tr>
<tr class="qandadiv"><td align="left" valign="top" colspan="2"><h5 class="title">
<a name="id-1.2.5.3.3.4"></a>4. GtkTextView</h5></td></tr>
<tr class="question">
<td align="left" valign="top">
<a name="id-1.2.5.3.3.4.2"></a><a name="id-1.2.5.3.3.4.2.1"></a><p><b>4.1.</b></p>
</td>
<td align="left" valign="top"><p>
How do I get the contents of the entire text widget as a string?
</p></td>
</tr>
<tr class="answer">
<td align="left" valign="top"></td>
<td align="left" valign="top">
<p>
See <a class="link" href="GtkTextBuffer.html#gtk-text-buffer-get-bounds" title="gtk_text_buffer_get_bounds ()"><code class="function">gtk_text_buffer_get_bounds()</code></a> and <a class="link" href="GtkTextBuffer.html#gtk-text-buffer-get-text" title="gtk_text_buffer_get_text ()"><code class="function">gtk_text_buffer_get_text()</code></a>
or <a class="link" href="GtkTextIter.html#gtk-text-iter-get-text" title="gtk_text_iter_get_text ()"><code class="function">gtk_text_iter_get_text()</code></a>.
</p>
<p>
</p>
<div class="informalexample">
<table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
<tbody>
<tr>
<td class="listing_lines" align="right"><pre>1
2
3
4
5
6
7
8
9</pre></td>
<td class="listing_code"><pre class="programlisting"><span class="usertype">GtkTextIter</span><span class="normal"> start</span><span class="symbol">,</span><span class="normal"> end</span><span class="symbol">;</span>
<span class="usertype">GtkTextBuffer</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">buffer</span><span class="symbol">;</span>
<span class="type">char</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">text</span><span class="symbol">;</span>
<span class="normal">buffer </span><span class="symbol">=</span><span class="normal"> </span><span class="function"><a href="GtkTextView.html#gtk-text-view-get-buffer">gtk_text_view_get_buffer</a></span><span class="normal"> </span><span class="symbol">(</span><span class="function">GTK_TEXT_VIEW</span><span class="normal"> </span><span class="symbol">(</span><span class="normal">text_view</span><span class="symbol">));</span>
<span class="function"><a href="GtkTextBuffer.html#gtk-text-buffer-get-bounds">gtk_text_buffer_get_bounds</a></span><span class="normal"> </span><span class="symbol">(</span><span class="normal">buffer</span><span class="symbol">,</span><span class="normal"> </span><span class="symbol">&</span><span class="normal">start</span><span class="symbol">,</span><span class="normal"> </span><span class="symbol">&</span><span class="normal">end</span><span class="symbol">);</span>
<span class="normal">text </span><span class="symbol">=</span><span class="normal"> </span><span class="function"><a href="GtkTextIter.html#gtk-text-iter-get-text">gtk_text_iter_get_text</a></span><span class="normal"> </span><span class="symbol">(&</span><span class="normal">start</span><span class="symbol">,</span><span class="normal"> </span><span class="symbol">&</span><span class="normal">end</span><span class="symbol">);</span>
<span class="comment">/* use text */</span>
<span class="function">g_free</span><span class="normal"> </span><span class="symbol">(</span><span class="normal">text</span><span class="symbol">);</span></pre></td>
</tr>
</tbody>
</table>
</div>
<p>
</p>
</td>
</tr>
<tr class="question">
<td align="left" valign="top">
<a name="id-1.2.5.3.3.4.3"></a><a name="id-1.2.5.3.3.4.3.1"></a><p><b>4.2.</b></p>
</td>
<td align="left" valign="top"><p>
How do I make a text widget display its complete contents in a specific font?
</p></td>
</tr>
<tr class="answer">
<td align="left" valign="top"></td>
<td align="left" valign="top">
<p>
If you use <a class="link" href="GtkTextBuffer.html#gtk-text-buffer-insert-with-tags" title="gtk_text_buffer_insert_with_tags ()"><code class="function">gtk_text_buffer_insert_with_tags()</code></a> with appropriate tags to
select the font, the inserted text will have the desired appearance, but
text typed in by the user before or after the tagged block will appear in
the default style.
</p>
<p>
To ensure that all text has the desired appearance, use
<a class="link" href="GtkWidget.html#gtk-widget-override-font" title="gtk_widget_override_font ()"><code class="function">gtk_widget_override_font()</code></a> to change the default font for the widget.
</p>
</td>
</tr>
<tr class="question">
<td align="left" valign="top">
<a name="id-1.2.5.3.3.4.4"></a><a name="id-1.2.5.3.3.4.4.1"></a><p><b>4.3.</b></p>
</td>
<td align="left" valign="top"><p>
How do I make a text view scroll to the end of the buffer automatically ?
</p></td>
</tr>
<tr class="answer">
<td align="left" valign="top"></td>
<td align="left" valign="top">
<p>
A good way to keep a text buffer scrolled to the end is to place a
<a class="link" href="GtkTextMark.html" title="GtkTextMark">mark</a> at the end of the buffer, and
give it right gravity. The gravity has the effect that text inserted
at the mark gets inserted <span class="emphasis"><em>before</em></span>, keeping the mark
at the end.
</p>
<p>
To ensure that the end of the buffer remains visible, use
<a class="link" href="GtkTextView.html#gtk-text-view-scroll-to-mark" title="gtk_text_view_scroll_to_mark ()"><code class="function">gtk_text_view_scroll_to_mark()</code></a> to scroll to the mark after
inserting new text.
</p>
<p>
The gtk-demo application contains an example of this technique.
</p>
</td>
</tr>
<tr class="qandadiv"><td align="left" valign="top" colspan="2"><h5 class="title">
<a name="id-1.2.5.3.3.5"></a>5. <a class="link" href="GtkTreeView.html" title="GtkTreeView"><span class="type">GtkTreeView</span></a>
</h5></td></tr>
<tr class="question">
<td align="left" valign="top">
<a name="id-1.2.5.3.3.5.2"></a><a name="id-1.2.5.3.3.5.2.1"></a><p><b>5.1.</b></p>
</td>
<td align="left" valign="top"><p>
How do I associate some data with a row in the tree?
</p></td>
</tr>
<tr class="answer">
<td align="left" valign="top"></td>
<td align="left" valign="top"><p>
Remember that the <a class="link" href="GtkTreeModel.html" title="GtkTreeModel"><span class="type">GtkTreeModel</span></a> columns don't necessarily have to be
displayed. So you can put non-user-visible data in your model just
like any other data, and retrieve it with <a class="link" href="GtkTreeModel.html#gtk-tree-model-get" title="gtk_tree_model_get ()"><code class="function">gtk_tree_model_get()</code></a>.
See the <a class="link" href="TreeWidget.html" title="Tree and List Widget Overview">tree widget overview</a>.
</p></td>
</tr>
<tr class="question">
<td align="left" valign="top">
<a name="id-1.2.5.3.3.5.3"></a><a name="id-1.2.5.3.3.5.3.1"></a><p><b>5.2.</b></p>
</td>
<td align="left" valign="top"><p>
How do I put an image and some text in the same column?
</p></td>
</tr>
<tr class="answer">
<td align="left" valign="top"></td>
<td align="left" valign="top"><p>
You can pack more than one <a class="link" href="GtkCellRenderer.html" title="GtkCellRenderer"><span class="type">GtkCellRenderer</span></a> into a single <a class="link" href="GtkTreeViewColumn.html" title="GtkTreeViewColumn"><span class="type">GtkTreeViewColumn</span></a>
using <a class="link" href="GtkTreeViewColumn.html#gtk-tree-view-column-pack-start" title="gtk_tree_view_column_pack_start ()"><code class="function">gtk_tree_view_column_pack_start()</code></a> or <a class="link" href="GtkTreeViewColumn.html#gtk-tree-view-column-pack-end" title="gtk_tree_view_column_pack_end ()"><code class="function">gtk_tree_view_column_pack_end()</code></a>.
So pack both a <a class="link" href="GtkCellRendererPixbuf.html" title="GtkCellRendererPixbuf"><span class="type">GtkCellRendererPixbuf</span></a> and a <a class="link" href="GtkCellRendererText.html" title="GtkCellRendererText"><span class="type">GtkCellRendererText</span></a> into the
column.
</p></td>
</tr>
<tr class="question">
<td align="left" valign="top">
<a name="id-1.2.5.3.3.5.4"></a><a name="id-1.2.5.3.3.5.4.1"></a><p><b>5.3.</b></p>
</td>
<td align="left" valign="top"><p>
I can set data easily on my <a class="link" href="GtkTreeStore.html" title="GtkTreeStore"><span class="type">GtkTreeStore</span></a>/<a class="link" href="GtkListStore.html" title="GtkListStore"><span class="type">GtkListStore</span></a> models using
<a class="link" href="GtkListStore.html#gtk-list-store-set" title="gtk_list_store_set ()"><code class="function">gtk_list_store_set()</code></a> and <a class="link" href="GtkTreeStore.html#gtk-tree-store-set" title="gtk_tree_store_set ()"><code class="function">gtk_tree_store_set()</code></a>, but can't read it back?
</p></td>
</tr>
<tr class="answer">
<td align="left" valign="top"></td>
<td align="left" valign="top"><p>
Both the <a class="link" href="GtkTreeStore.html" title="GtkTreeStore"><span class="type">GtkTreeStore</span></a> and the <a class="link" href="GtkListStore.html" title="GtkListStore"><span class="type">GtkListStore</span></a> implement the <a class="link" href="GtkTreeModel.html" title="GtkTreeModel"><span class="type">GtkTreeModel</span></a>
interface. Consequentially, you can use any function this interface
implements. The easiest way to read a set of data back is to use
<a class="link" href="GtkTreeModel.html#gtk-tree-model-get" title="gtk_tree_model_get ()"><code class="function">gtk_tree_model_get()</code></a>.
</p></td>
</tr>
<tr class="question">
<td align="left" valign="top">
<a name="id-1.2.5.3.3.5.5"></a><a name="id-1.2.5.3.3.5.5.1"></a><p><b>5.4.</b></p>
</td>
<td align="left" valign="top"><p>
How do I change the way that numbers are formatted by <a class="link" href="GtkTreeView.html" title="GtkTreeView"><span class="type">GtkTreeView</span></a>?
</p></td>
</tr>
<tr class="answer">
<td align="left" valign="top"></td>
<td align="left" valign="top">
<p>
Use <a class="link" href="GtkTreeView.html#gtk-tree-view-insert-column-with-data-func" title="gtk_tree_view_insert_column_with_data_func ()"><code class="function">gtk_tree_view_insert_column_with_data_func()</code></a>
or <a class="link" href="GtkTreeViewColumn.html#gtk-tree-view-column-set-cell-data-func" title="gtk_tree_view_column_set_cell_data_func ()"><code class="function">gtk_tree_view_column_set_cell_data_func()</code></a> and do the conversion
from number to string yourself (with, say, <code class="function">g_strdup_printf()</code>).
</p>
<p>
The following example demonstrates this:
</p>
<div class="informalexample">
<table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
<tbody>
<tr>
<td class="listing_lines" align="right"><pre>1
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64</pre></td>
<td class="listing_code"><pre class="programlisting"><span class="keyword">enum</span>
<span class="cbracket">{</span>
<span class="normal"> DOUBLE_COLUMN</span><span class="symbol">,</span>
<span class="normal"> N_COLUMNS</span>
<span class="cbracket">}</span><span class="symbol">;</span>
<span class="usertype">GtkListStore</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">mycolumns</span><span class="symbol">;</span>
<span class="usertype">GtkTreeView</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">treeview</span><span class="symbol">;</span>
<span class="type">void</span>
<span class="function">my_cell_double_to_text</span><span class="normal"> </span><span class="symbol">(</span><span class="usertype">GtkTreeViewColumn</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">tree_column</span><span class="symbol">,</span>
<span class="normal"> </span><span class="usertype">GtkCellRenderer</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">cell</span><span class="symbol">,</span>
<span class="normal"> </span><span class="usertype">GtkTreeModel</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">tree_model</span><span class="symbol">,</span>
<span class="normal"> </span><span class="usertype">GtkTreeIter</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">iter</span><span class="symbol">,</span>
<span class="normal"> </span><span class="usertype">gpointer</span><span class="normal"> data</span><span class="symbol">)</span>
<span class="cbracket">{</span>
<span class="normal"> </span><span class="usertype">GtkCellRendererText</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">cell_text </span><span class="symbol">=</span><span class="normal"> </span><span class="symbol">(</span><span class="normal"><a href="GtkCellRendererText.html#GtkCellRendererText-struct">GtkCellRendererText</a> </span><span class="symbol">*)</span><span class="normal">cell</span><span class="symbol">;</span>
<span class="normal"> </span><span class="usertype">gdouble</span><span class="normal"> d</span><span class="symbol">;</span>
<span class="normal"> </span><span class="usertype">gchar</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">text</span><span class="symbol">;</span>
<span class="normal"> </span><span class="comment">/* Get the double value from the model. */</span>
<span class="normal"> </span><span class="function"><a href="GtkTreeModel.html#gtk-tree-model-get">gtk_tree_model_get</a></span><span class="normal"> </span><span class="symbol">(</span><span class="normal">tree_model</span><span class="symbol">,</span><span class="normal"> iter</span><span class="symbol">,</span><span class="normal"> </span><span class="symbol">(</span><span class="normal">gint</span><span class="symbol">)</span><span class="normal">data</span><span class="symbol">,</span><span class="normal"> </span><span class="symbol">&</span><span class="normal">d</span><span class="symbol">,</span><span class="normal"> </span><span class="symbol">-</span><span class="number">1</span><span class="symbol">);</span>
<span class="normal"> </span><span class="comment">/* Now we can format the value ourselves. */</span>
<span class="normal"> text </span><span class="symbol">=</span><span class="normal"> </span><span class="function">g_strdup_printf</span><span class="normal"> </span><span class="symbol">(</span><span class="string">"%.2f"</span><span class="symbol">,</span><span class="normal"> d</span><span class="symbol">);</span>
<span class="normal"> </span><span class="function">g_object_set</span><span class="normal"> </span><span class="symbol">(</span><span class="normal">cell</span><span class="symbol">,</span><span class="normal"> </span><span class="string">"text"</span><span class="symbol">,</span><span class="normal"> text</span><span class="symbol">,</span><span class="normal"> NULL</span><span class="symbol">);</span>
<span class="normal"> </span><span class="function">g_free</span><span class="normal"> </span><span class="symbol">(</span><span class="normal">text</span><span class="symbol">);</span>
<span class="cbracket">}</span>
<span class="type">void</span>
<span class="function">set_up_new_columns</span><span class="normal"> </span><span class="symbol">(</span><span class="usertype">GtkTreeView</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">myview</span><span class="symbol">)</span>
<span class="cbracket">{</span>
<span class="normal"> </span><span class="usertype">GtkCellRendererText</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">renderer</span><span class="symbol">;</span>
<span class="normal"> </span><span class="usertype">GtkTreeViewColumn</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">column</span><span class="symbol">;</span>
<span class="normal"> </span><span class="usertype">GtkListStore</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">mycolumns</span><span class="symbol">;</span>
<span class="normal"> </span><span class="comment">/* Create the data model and associate it with the given TreeView */</span>
<span class="normal"> mycolumns </span><span class="symbol">=</span><span class="normal"> </span><span class="function"><a href="GtkListStore.html#gtk-list-store-new">gtk_list_store_new</a></span><span class="normal"> </span><span class="symbol">(</span><span class="normal">N_COLUMNS</span><span class="symbol">,</span><span class="normal"> G_TYPE_DOUBLE</span><span class="symbol">);</span>
<span class="normal"> </span><span class="function"><a href="GtkTreeView.html#gtk-tree-view-set-model">gtk_tree_view_set_model</a></span><span class="normal"> </span><span class="symbol">(</span><span class="normal">myview</span><span class="symbol">,</span><span class="normal"> </span><span class="function">GTK_TREE_MODEL</span><span class="normal"> </span><span class="symbol">(</span><span class="normal">mycolumns</span><span class="symbol">));</span>
<span class="normal"> </span><span class="comment">/* Create a GtkCellRendererText */</span>
<span class="normal"> renderer </span><span class="symbol">=</span><span class="normal"> </span><span class="function"><a href="GtkCellRendererText.html#gtk-cell-renderer-text-new">gtk_cell_renderer_text_new</a></span><span class="normal"> </span><span class="symbol">();</span>
<span class="normal"> </span><span class="comment">/* Create a new column that has a title ("Example column"),</span>
<span class="comment"> * uses the above created renderer that will render the double</span>
<span class="comment"> * value into text from the associated model's rows.</span>
<span class="comment"> */</span>
<span class="normal"> column </span><span class="symbol">=</span><span class="normal"> </span><span class="function"><a href="GtkTreeViewColumn.html#gtk-tree-view-column-new">gtk_tree_view_column_new</a></span><span class="normal"> </span><span class="symbol">();</span>
<span class="normal"> </span><span class="function"><a href="GtkTreeViewColumn.html#gtk-tree-view-column-set-title">gtk_tree_view_column_set_title</a></span><span class="normal"> </span><span class="symbol">(</span><span class="normal">column</span><span class="symbol">,</span><span class="normal"> </span><span class="string">"Example column"</span><span class="symbol">);</span>
<span class="normal"> renderer </span><span class="symbol">=</span><span class="normal"> </span><span class="function"><a href="GtkCellRendererText.html#gtk-cell-renderer-text-new">gtk_cell_renderer_text_new</a></span><span class="normal"> </span><span class="symbol">();</span>
<span class="normal"> </span><span class="function"><a href="GtkTreeViewColumn.html#gtk-tree-view-column-pack-start">gtk_tree_view_column_pack_start</a></span><span class="normal"> </span><span class="symbol">(</span><span class="normal">column</span><span class="symbol">,</span><span class="normal"> renderer</span><span class="symbol">,</span><span class="normal"> TRUE</span><span class="symbol">);</span>
<span class="normal"> </span><span class="comment">/* Append the new column after the GtkTreeView's previous columns. */</span>
<span class="normal"> </span><span class="function"><a href="GtkTreeView.html#gtk-tree-view-append-column">gtk_tree_view_append_column</a></span><span class="normal"> </span><span class="symbol">(</span><span class="function">GTK_TREE_VIEW</span><span class="normal"> </span><span class="symbol">(</span><span class="normal">myview</span><span class="symbol">),</span><span class="normal"> column</span><span class="symbol">);</span>
<span class="normal"> </span><span class="comment">/* Since we created the column by hand, we can set it up for our</span>
<span class="comment"> * needs, e.g. set its minimum and maximum width, etc.</span>
<span class="comment"> */</span>
<span class="normal"> </span><span class="comment">/* Set up a custom function that will be called when the column content</span>
<span class="comment"> * is rendered. We use the func_data pointer as an index into our</span>
<span class="comment"> * model. This is convenient when using multi column lists.</span>
<span class="comment"> */</span>
<span class="normal"> </span><span class="function"><a href="GtkTreeViewColumn.html#gtk-tree-view-column-set-cell-data-func">gtk_tree_view_column_set_cell_data_func</a></span><span class="normal"> </span><span class="symbol">(</span><span class="normal">column</span><span class="symbol">,</span><span class="normal"> renderer</span><span class="symbol">,</span>
<span class="normal"> my_cell_double_to_text</span><span class="symbol">,</span>
<span class="normal"> </span><span class="symbol">(</span><span class="normal">gpointer</span><span class="symbol">)</span><span class="normal">DOUBLE_COLUMN</span><span class="symbol">,</span><span class="normal"> NULL</span><span class="symbol">);</span>
<span class="cbracket">}</span></pre></td>
</tr>
</tbody>
</table>
</div>
<p>
</p>
</td>
</tr>
<tr class="question">
<td align="left" valign="top">
<a name="id-1.2.5.3.3.5.6"></a><a name="id-1.2.5.3.3.5.6.1"></a><p><b>5.5.</b></p>
</td>
<td align="left" valign="top"><p>
How do I hide the expander arrows in my tree view ?
</p></td>
</tr>
<tr class="answer">
<td align="left" valign="top"></td>
<td align="left" valign="top"><p>
Set the expander-column property of the tree view to a hidden column.
See <a class="link" href="GtkTreeView.html#gtk-tree-view-set-expander-column" title="gtk_tree_view_set_expander_column ()"><code class="function">gtk_tree_view_set_expander_column()</code></a> and <a class="link" href="GtkTreeViewColumn.html#gtk-tree-view-column-set-visible" title="gtk_tree_view_column_set_visible ()"><code class="function">gtk_tree_view_column_set_visible()</code></a>.
</p></td>
</tr>
<tr class="qandadiv"><td align="left" valign="top" colspan="2"><h5 class="title">
<a name="id-1.2.5.3.3.6"></a>6. Using cairo with GTK+</h5></td></tr>
<tr class="question">
<td align="left" valign="top">
<a name="id-1.2.5.3.3.6.2"></a><a name="id-1.2.5.3.3.6.2.1"></a><p><b>6.1.</b></p>
</td>
<td align="left" valign="top"><p>
How do I use cairo to draw in GTK+ applications ?
</p></td>
</tr>
<tr class="answer">
<td align="left" valign="top"></td>
<td align="left" valign="top">
<p>
The <a class="link" href="GtkWidget.html#GtkWidget-draw" title="The “draw” signal"><span class="type">“draw”</span></a> signal gets a ready-to-use cairo context
as parameter that you should use.
</p>
<p>
All drawing in GTK+ is normally done in a draw handler, and GTK+
creates a temporary pixmap for double-buffering the drawing.
It is possible to turn off double-buffering, with
<a class="link" href="GtkWidget.html#gtk-widget-set-double-buffered" title="gtk_widget_set_double_buffered ()"><code class="function">gtk_widget_set_double_buffered()</code></a>, but this is not ideal,
since it can cause some flickering.
</p>
</td>
</tr>
<tr class="question">
<td align="left" valign="top">
<a name="id-1.2.5.3.3.6.3"></a><a name="id-1.2.5.3.3.6.3.1"></a><p><b>6.2.</b></p>
</td>
<td align="left" valign="top"><p>
Can I improve the performance of my application by using the
Glitz or GL backend of cairo ?
</p></td>
</tr>
<tr class="answer">
<td align="left" valign="top"></td>
<td align="left" valign="top"><p>
No. The GDK X11 backend uses the cairo X backend (and the other
GDK backends use their respective native cairo backends). The
GTK+ developers believe that the best way to improving the GDK
drawing performance is to optimize the cairo X backend and the
relevant code paths in the X server that is uses (mostly the
Render extension).
</p></td>
</tr>
<tr class="question">
<td align="left" valign="top">
<a name="id-1.2.5.3.3.6.4"></a><a name="id-1.2.5.3.3.6.4.1"></a><p><b>6.3.</b></p>
</td>
<td align="left" valign="top"><p>
Can I use cairo to draw on a <span class="type">GdkPixbuf</span> ?
</p></td>
</tr>
<tr class="answer">
<td align="left" valign="top"></td>
<td align="left" valign="top"><p>
No, at least not yet. The cairo image surface does not support the
pixel format used by GdkPixbuf.
</p></td>
</tr>
</tbody>
</table>
</div>
</div>
<div class="footnotes">
<br><hr style="width:100; text-align:left;margin-left: 0">
<div id="ftn.id-1.2.5.3.3.1.12.2.1.2" class="footnote"><p><a href="#id-1.2.5.3.3.1.12.2.1.2" class="para"><sup class="para">[1] </sup></a> If the file load fails,
<a class="link" href="GtkImage.html#gtk-image-new-from-file" title="gtk_image_new_from_file ()"><code class="function">gtk_image_new_from_file()</code></a> will display no image graphic — to detect
a failed load yourself, use <code class="function">gdk_pixbuf_new_from_file()</code> directly, then
<a class="link" href="GtkImage.html#gtk-image-new-from-pixbuf" title="gtk_image_new_from_pixbuf ()"><code class="function">gtk_image_new_from_pixbuf()</code></a>.</p></div>
</div>
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