124 lines
5.4 KiB
HTML
124 lines
5.4 KiB
HTML
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
|
|
<html>
|
|
<!-- Copyright (C) 1988-2016 Free Software Foundation, Inc.
|
|
|
|
Permission is granted to copy, distribute and/or modify this document
|
|
under the terms of the GNU Free Documentation License, Version 1.3 or
|
|
any later version published by the Free Software Foundation; with the
|
|
Invariant Sections being "Funding Free Software", the Front-Cover
|
|
Texts being (a) (see below), and with the Back-Cover Texts being (b)
|
|
(see below). A copy of the license is included in the section entitled
|
|
"GNU Free Documentation License".
|
|
|
|
(a) The FSF's Front-Cover Text is:
|
|
|
|
A GNU Manual
|
|
|
|
(b) The FSF's Back-Cover Text is:
|
|
|
|
You have freedom to copy and modify this GNU Manual, like GNU
|
|
software. Copies published by the Free Software Foundation raise
|
|
funds for GNU development. -->
|
|
<!-- Created by GNU Texinfo 5.2, http://www.gnu.org/software/texinfo/ -->
|
|
<head>
|
|
<title>Using the GNU Compiler Collection (GCC): Bound member functions</title>
|
|
|
|
<meta name="description" content="Using the GNU Compiler Collection (GCC): Bound member functions">
|
|
<meta name="keywords" content="Using the GNU Compiler Collection (GCC): Bound member functions">
|
|
<meta name="resource-type" content="document">
|
|
<meta name="distribution" content="global">
|
|
<meta name="Generator" content="makeinfo">
|
|
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
|
|
<link href="index.html#Top" rel="start" title="Top">
|
|
<link href="Option-Index.html#Option-Index" rel="index" title="Option Index">
|
|
<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
|
|
<link href="C_002b_002b-Extensions.html#C_002b_002b-Extensions" rel="up" title="C++ Extensions">
|
|
<link href="C_002b_002b-Attributes.html#C_002b_002b-Attributes" rel="next" title="C++ Attributes">
|
|
<link href="Template-Instantiation.html#Template-Instantiation" rel="prev" title="Template Instantiation">
|
|
<style type="text/css">
|
|
<!--
|
|
a.summary-letter {text-decoration: none}
|
|
blockquote.smallquotation {font-size: smaller}
|
|
div.display {margin-left: 3.2em}
|
|
div.example {margin-left: 3.2em}
|
|
div.indentedblock {margin-left: 3.2em}
|
|
div.lisp {margin-left: 3.2em}
|
|
div.smalldisplay {margin-left: 3.2em}
|
|
div.smallexample {margin-left: 3.2em}
|
|
div.smallindentedblock {margin-left: 3.2em; font-size: smaller}
|
|
div.smalllisp {margin-left: 3.2em}
|
|
kbd {font-style:oblique}
|
|
pre.display {font-family: inherit}
|
|
pre.format {font-family: inherit}
|
|
pre.menu-comment {font-family: serif}
|
|
pre.menu-preformatted {font-family: serif}
|
|
pre.smalldisplay {font-family: inherit; font-size: smaller}
|
|
pre.smallexample {font-size: smaller}
|
|
pre.smallformat {font-family: inherit; font-size: smaller}
|
|
pre.smalllisp {font-size: smaller}
|
|
span.nocodebreak {white-space:nowrap}
|
|
span.nolinebreak {white-space:nowrap}
|
|
span.roman {font-family:serif; font-weight:normal}
|
|
span.sansserif {font-family:sans-serif; font-weight:normal}
|
|
ul.no-bullet {list-style: none}
|
|
-->
|
|
</style>
|
|
|
|
|
|
</head>
|
|
|
|
<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
|
|
<a name="Bound-member-functions"></a>
|
|
<div class="header">
|
|
<p>
|
|
Next: <a href="C_002b_002b-Attributes.html#C_002b_002b-Attributes" accesskey="n" rel="next">C++ Attributes</a>, Previous: <a href="Template-Instantiation.html#Template-Instantiation" accesskey="p" rel="prev">Template Instantiation</a>, Up: <a href="C_002b_002b-Extensions.html#C_002b_002b-Extensions" accesskey="u" rel="up">C++ Extensions</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
|
|
</div>
|
|
<hr>
|
|
<a name="Extracting-the-Function-Pointer-from-a-Bound-Pointer-to-Member-Function"></a>
|
|
<h3 class="section">7.6 Extracting the Function Pointer from a Bound Pointer to Member Function</h3>
|
|
<a name="index-pmf"></a>
|
|
<a name="index-pointer-to-member-function"></a>
|
|
<a name="index-bound-pointer-to-member-function"></a>
|
|
|
|
<p>In C++, pointer to member functions (PMFs) are implemented using a wide
|
|
pointer of sorts to handle all the possible call mechanisms; the PMF
|
|
needs to store information about how to adjust the ‘<samp>this</samp>’ pointer,
|
|
and if the function pointed to is virtual, where to find the vtable, and
|
|
where in the vtable to look for the member function. If you are using
|
|
PMFs in an inner loop, you should really reconsider that decision. If
|
|
that is not an option, you can extract the pointer to the function that
|
|
would be called for a given object/PMF pair and call it directly inside
|
|
the inner loop, to save a bit of time.
|
|
</p>
|
|
<p>Note that you still pay the penalty for the call through a
|
|
function pointer; on most modern architectures, such a call defeats the
|
|
branch prediction features of the CPU. This is also true of normal
|
|
virtual function calls.
|
|
</p>
|
|
<p>The syntax for this extension is
|
|
</p>
|
|
<div class="smallexample">
|
|
<pre class="smallexample">extern A a;
|
|
extern int (A::*fp)();
|
|
typedef int (*fptr)(A *);
|
|
|
|
fptr p = (fptr)(a.*fp);
|
|
</pre></div>
|
|
|
|
<p>For PMF constants (i.e. expressions of the form ‘<samp>&Klasse::Member</samp>’),
|
|
no object is needed to obtain the address of the function. They can be
|
|
converted to function pointers directly:
|
|
</p>
|
|
<div class="smallexample">
|
|
<pre class="smallexample">fptr p1 = (fptr)(&A::foo);
|
|
</pre></div>
|
|
|
|
<a name="index-Wno_002dpmf_002dconversions-1"></a>
|
|
<p>You must specify <samp>-Wno-pmf-conversions</samp> to use this extension.
|
|
</p>
|
|
|
|
|
|
|
|
</body>
|
|
</html>
|