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<html xmlns:cf="http://docbook.sourceforge.net/xmlns/chunkfast/1.0"><head><meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"><title>Type Conversion Macros</title><meta name="generator" content="DocBook XSL Stylesheets V1.69.0"><link rel="start" href="index.html" title="GLib Reference Manual"><link rel="up" href="glib-fundamentals.html" title="GLib Fundamentals"><link rel="prev" href="glib-Standard-Macros.html" title="Standard Macros"><link rel="next" href="glib-Byte-Order-Macros.html" title="Byte Order Macros"><meta name="generator" content="GTK-Doc V1.4 (XML mode)"><link rel="stylesheet" href="style.css" type="text/css"><link rel="chapter" href="glib.html" title="GLib Overview"><link rel="chapter" href="glib-fundamentals.html" title="GLib Fundamentals"><link rel="chapter" href="glib-core.html" title="GLib Core Application Support"><link rel="chapter" href="glib-utilities.html" title="GLib Utilities"><link rel="chapter" href="glib-data-types.html" title="GLib Data Types"><link rel="chapter" href="tools.html" title="GLib Tools"><link rel="index" href="ix01.html" title="Index"><link rel="index" href="ix02.html" title="Index of deprecated symbols"><link rel="index" href="ix03.html" title="Index of new symbols in 2.2"><link rel="index" href="ix04.html" title="Index of new symbols in 2.4"><link rel="index" href="ix05.html" title="Index of new symbols in 2.6"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><table class="navigation" width="100%" summary="Navigation header" cellpadding="2" cellspacing="2"><tr valign="middle"><td><a accesskey="p" href="glib-Standard-Macros.html"><img src="left.png" width="24" height="24" border="0" alt="Prev"></a></td><td><a accesskey="u" href="glib-fundamentals.html"><img src="up.png" width="24" height="24" border="0" alt="Up"></a></td><td><a accesskey="h" href="index.html"><img src="home.png" width="24" height="24" border="0" alt="Home"></a></td><th width="100%" align="center">GLib Reference Manual</th><td><a accesskey="n" href="glib-Byte-Order-Macros.html"><img src="right.png" width="24" height="24" border="0" alt="Next"></a></td></tr></table><div class="refentry" lang="en"><a name="glib-Type-Conversion-Macros"></a><div class="titlepage"></div><div class="refnamediv"><table width="100%"><tr><td valign="top"><h2><span class="refentrytitle">Type Conversion Macros</span></h2><p>Type Conversion Macros — portably storing integers in pointer variables.</p></td><td valign="top" align="right"></td></tr></table></div><div class="refsynopsisdiv"><h2>Synopsis</h2><pre class="synopsis">#include <glib.h>#define <a href="glib-Type-Conversion-Macros.html#GINT-TO-POINTER:CAPS">GINT_TO_POINTER</a> (i)#define <a href="glib-Type-Conversion-Macros.html#GPOINTER-TO-INT:CAPS">GPOINTER_TO_INT</a> (p)#define <a href="glib-Type-Conversion-Macros.html#GUINT-TO-POINTER:CAPS">GUINT_TO_POINTER</a> (u)#define <a href="glib-Type-Conversion-Macros.html#GPOINTER-TO-UINT:CAPS">GPOINTER_TO_UINT</a> (p)#define <a href="glib-Type-Conversion-Macros.html#GSIZE-TO-POINTER:CAPS">GSIZE_TO_POINTER</a> (s)#define <a href="glib-Type-Conversion-Macros.html#GPOINTER-TO-SIZE:CAPS">GPOINTER_TO_SIZE</a> (p)</pre></div><div class="refsect1" lang="en"><a name="id2826957"></a><h2>Description</h2><p>Many times GLib, GTK+, and other libraries allow you to pass "userdata" to a callback, in the form of a void pointer. From time to timeyou want to pass an integer instead of a pointer. You could allocatean integer, with something like:</p><div class="informalexample"><pre class="programlisting"> int *ip = g_new (int, 1); *ip = 42;</pre></div><p>But this is inconvenient, and it's annoying to have to free the memory at some later time.</p><p>Pointers are always at least 32 bits in size (on all platforms GLibintends to support). Thus you can store at least 32-bit integer valuesin a pointer value. Naively, you might try this, but it's incorrect:</p><div class="informalexample"><pre class="programlisting"> gpointer p; int i; p = (void*) 42; i = (int) p;</pre></div><p>Again, that example was <span class="emphasis"><em>not</em></span> correct, don't copy it. The problem is that on some systems you need to do this:</p><div class="informalexample"><pre class="programlisting"> gpointer p; int i; p = (void*) (long) 42; i = (int) (long) p;</pre></div><p>So <a href="glib-Type-Conversion-Macros.html#GPOINTER-TO-INT:CAPS"><code class="function">GPOINTER_TO_INT()</code></a>, <a href="glib-Type-Conversion-Macros.html#GINT-TO-POINTER:CAPS"><code class="function">GINT_TO_POINTER()</code></a>, etc. do the right thingon the current platform.</p><p></p><div class="warning" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Warning</h3><p>YOU MAY NOT STORE POINTERS IN INTEGERS. THIS IS NOT PORTABLE IN ANYWAY SHAPE OR FORM. These macros <span class="emphasis"><em>ONLY</em></span> allowstoring integers in pointers, and only preserve 32 bits of theinteger; values outside the range of a 32-bit integer will be mangled.</p></div><p></p></div><div class="refsect1" lang="en"><a name="id2827048"></a><h2>Details</h2><div class="refsect2" lang="en"><a name="id2827054"></a><h3><a name="GINT-TO-POINTER:CAPS"></a>GINT_TO_POINTER()</h3><a class="indexterm" name="id2827065"></a><pre class="programlisting">#define GINT_TO_POINTER(i) ((gpointer) (i))</pre><p>Stuffs an integer into a pointer type.</p><p>Remember, YOU MAY NOT STORE POINTERS IN INTEGERS. THIS IS NOT PORTABLEIN ANY WAY SHAPE OR FORM. These macros <span class="emphasis"><em>ONLY</em></span> allowstoring integers in pointers, and only preserve 32 bits of theinteger; values outside the range of a 32-bit integer will be mangled.</p><div class="variablelist"><table border="0"><col align="left" valign="top"><tbody><tr><td><span class="term"><em class="parameter"><code>i</code></em> :</span></td><td>integer to stuff into a pointer.</td></tr></tbody></table></div></div><hr><div class="refsect2" lang="en"><a name="id2827110"></a><h3><a name="GPOINTER-TO-INT:CAPS"></a>GPOINTER_TO_INT()</h3><a class="indexterm" name="id2827121"></a><pre class="programlisting">#define GPOINTER_TO_INT(p) ((gint) (p))</pre><p>Extracts an integer from a pointer. The integer must havebeen stored in the pointer with <a href="glib-Type-Conversion-Macros.html#GINT-TO-POINTER:CAPS"><code class="function">GINT_TO_POINTER()</code></a>.</p><p>Remember, YOU MAY NOT STORE POINTERS IN INTEGERS. THIS IS NOT PORTABLEIN ANY WAY SHAPE OR FORM. These macros <span class="emphasis"><em>ONLY</em></span> allowstoring integers in pointers, and only preserve 32 bits of theinteger; values outside the range of a 32-bit integer will be mangled.</p><div class="variablelist"><table border="0"><col align="left" valign="top"><tbody><tr><td><span class="term"><em class="parameter"><code>p</code></em> :</span></td><td>pointer containing an integer.</td></tr></tbody></table></div></div><hr><div class="refsect2" lang="en"><a name="id2827178"></a><h3><a name="GUINT-TO-POINTER:CAPS"></a>GUINT_TO_POINTER()</h3><a class="indexterm" name="id2827189"></a><pre class="programlisting">#define GUINT_TO_POINTER(u) ((gpointer) (u))</pre><p>Stuffs an unsigned integer into a pointer type.</p><div class="variablelist"><table border="0"><col align="left" valign="top"><tbody><tr><td><span class="term"><em class="parameter"><code>u</code></em> :</span></td><td>unsigned integer to stuff into the pointer.</td></tr></tbody></table></div></div><hr><div class="refsect2" lang="en"><a name="id2827224"></a><h3><a name="GPOINTER-TO-UINT:CAPS"></a>GPOINTER_TO_UINT()</h3><a class="indexterm" name="id2827235"></a><pre class="programlisting">#define GPOINTER_TO_UINT(p) ((guint) (p))</pre><p>Extracts an unsigned integer from a pointer. The integer must havebeen stored in the pointer with <a href="glib-Type-Conversion-Macros.html#GUINT-TO-POINTER:CAPS"><code class="function">GUINT_TO_POINTER()</code></a>.</p><div class="variablelist"><table border="0"><col align="left" valign="top"><tbody><tr><td><span class="term"><em class="parameter"><code>p</code></em> :</span></td><td>pointer to extract an unsigned integer from.</td></tr></tbody></table></div></div><hr><div class="refsect2" lang="en"><a name="id2827281"></a><h3><a name="GSIZE-TO-POINTER:CAPS"></a>GSIZE_TO_POINTER()</h3><a class="indexterm" name="id2827292"></a><pre class="programlisting">#define GSIZE_TO_POINTER(s) ((gpointer) (gsize) (s))</pre><p>Stuffs a <a href="glib-Basic-Types.html#gsize"><span class="type">gsize</span></a> into a pointer type.</p><div class="variablelist"><table border="0"><col align="left" valign="top"><tbody><tr><td><span class="term"><em class="parameter"><code>s</code></em> :</span></td><td><a href="glib-Basic-Types.html#gsize"><span class="type">gsize</span></a> to stuff into the pointer.</td></tr></tbody></table></div></div><hr><div class="refsect2" lang="en"><a name="id2827340"></a><h3><a name="GPOINTER-TO-SIZE:CAPS"></a>GPOINTER_TO_SIZE()</h3><a class="indexterm" name="id2827352"></a><pre class="programlisting">#define GPOINTER_TO_SIZE(p) ((gsize) (p))</pre><p>Extracts a <a href="glib-Basic-Types.html#gsize"><span class="type">gsize</span></a> from a pointer. The <a href="glib-Basic-Types.html#gsize"><span class="type">gsize</span></a> must havebeen stored in the pointer with <a href="glib-Type-Conversion-Macros.html#GSIZE-TO-POINTER:CAPS"><code class="function">GSIZE_TO_POINTER()</code></a>.</p><div class="variablelist"><table border="0"><col align="left" valign="top"><tbody><tr><td><span class="term"><em class="parameter"><code>p</code></em> :</span></td><td>pointer to extract a <a href="glib-Basic-Types.html#gsize"><span class="type">gsize</span></a> from.</td></tr></tbody></table></div></div></div></div><table class="navigation" width="100%" summary="Navigation footer" cellpadding="2" cellspacing="0"><tr valign="middle"><td align="left"><a accesskey="p" href="glib-Standard-Macros.html"><b><< Standard Macros</b></a></td><td align="right"><a accesskey="n" href="glib-Byte-Order-Macros.html"><b>Byte Order Macros >></b></a></td></tr></table></body></html>⌨️ 快捷键说明
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