1<html lang="en"> 2<head> 3<title>Restricted Pointers - Using the GNU Compiler Collection (GCC)</title> 4<meta http-equiv="Content-Type" content="text/html"> 5<meta name="description" content="Using the GNU Compiler Collection (GCC)"> 6<meta name="generator" content="makeinfo 4.13"> 7<link title="Top" rel="start" href="index.html#Top"> 8<link rel="up" href="C_002b_002b-Extensions.html#C_002b_002b-Extensions" title="C++ Extensions"> 9<link rel="prev" href="C_002b_002b-Volatiles.html#C_002b_002b-Volatiles" title="C++ Volatiles"> 10<link rel="next" href="Vague-Linkage.html#Vague-Linkage" title="Vague Linkage"> 11<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage"> 12<!-- 13Copyright (C) 1988-2013 Free Software Foundation, Inc. 14 15Permission is granted to copy, distribute and/or modify this document 16under the terms of the GNU Free Documentation License, Version 1.3 or 17any later version published by the Free Software Foundation; with the 18Invariant Sections being ``Funding Free Software'', the Front-Cover 19Texts being (a) (see below), and with the Back-Cover Texts being (b) 20(see below). A copy of the license is included in the section entitled 21``GNU Free Documentation License''. 22 23(a) The FSF's Front-Cover Text is: 24 25 A GNU Manual 26 27(b) The FSF's Back-Cover Text is: 28 29 You have freedom to copy and modify this GNU Manual, like GNU 30 software. Copies published by the Free Software Foundation raise 31 funds for GNU development.--> 32<meta http-equiv="Content-Style-Type" content="text/css"> 33<style type="text/css"><!-- 34 pre.display { font-family:inherit } 35 pre.format { font-family:inherit } 36 pre.smalldisplay { font-family:inherit; font-size:smaller } 37 pre.smallformat { font-family:inherit; font-size:smaller } 38 pre.smallexample { font-size:smaller } 39 pre.smalllisp { font-size:smaller } 40 span.sc { font-variant:small-caps } 41 span.roman { font-family:serif; font-weight:normal; } 42 span.sansserif { font-family:sans-serif; font-weight:normal; } 43--></style> 44<link rel="stylesheet" type="text/css" href="../cs.css"> 45</head> 46<body> 47<div class="node"> 48<a name="Restricted-Pointers"></a> 49<p> 50Next: <a rel="next" accesskey="n" href="Vague-Linkage.html#Vague-Linkage">Vague Linkage</a>, 51Previous: <a rel="previous" accesskey="p" href="C_002b_002b-Volatiles.html#C_002b_002b-Volatiles">C++ Volatiles</a>, 52Up: <a rel="up" accesskey="u" href="C_002b_002b-Extensions.html#C_002b_002b-Extensions">C++ Extensions</a> 53<hr> 54</div> 55 56<h3 class="section">7.2 Restricting Pointer Aliasing</h3> 57 58<p><a name="index-restricted-pointers-3505"></a><a name="index-restricted-references-3506"></a><a name="index-restricted-this-pointer-3507"></a> 59As with the C front end, G++ understands the C99 feature of restricted pointers, 60specified with the <code>__restrict__</code>, or <code>__restrict</code> type 61qualifier. Because you cannot compile C++ by specifying the <samp><span class="option">-std=c99</span></samp> 62language flag, <code>restrict</code> is not a keyword in C++. 63 64 <p>In addition to allowing restricted pointers, you can specify restricted 65references, which indicate that the reference is not aliased in the local 66context. 67 68<pre class="smallexample"> void fn (int *__restrict__ rptr, int &__restrict__ rref) 69 { 70 /* <span class="roman">...</span> */ 71 } 72</pre> 73 <p class="noindent">In the body of <code>fn</code>, <var>rptr</var> points to an unaliased integer and 74<var>rref</var> refers to a (different) unaliased integer. 75 76 <p>You may also specify whether a member function's <var>this</var> pointer is 77unaliased by using <code>__restrict__</code> as a member function qualifier. 78 79<pre class="smallexample"> void T::fn () __restrict__ 80 { 81 /* <span class="roman">...</span> */ 82 } 83</pre> 84 <p class="noindent">Within the body of <code>T::fn</code>, <var>this</var> has the effective 85definition <code>T *__restrict__ const this</code>. Notice that the 86interpretation of a <code>__restrict__</code> member function qualifier is 87different to that of <code>const</code> or <code>volatile</code> qualifier, in that it 88is applied to the pointer rather than the object. This is consistent with 89other compilers that implement restricted pointers. 90 91 <p>As with all outermost parameter qualifiers, <code>__restrict__</code> is 92ignored in function definition matching. This means you only need to 93specify <code>__restrict__</code> in a function definition, rather than 94in a function prototype as well. 95 96 </body></html> 97 98