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, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 141998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 152010 Free Software Foundation, Inc. 16 17Permission is granted to copy, distribute and/or modify this document 18under the terms of the GNU Free Documentation License, Version 1.3 or 19any later version published by the Free Software Foundation; with the 20Invariant Sections being ``Funding Free Software'', the Front-Cover 21Texts being (a) (see below), and with the Back-Cover Texts being (b) 22(see below). A copy of the license is included in the section entitled 23``GNU Free Documentation License''. 24 25(a) The FSF's Front-Cover Text is: 26 27 A GNU Manual 28 29(b) The FSF's Back-Cover Text is: 30 31 You have freedom to copy and modify this GNU Manual, like GNU 32 software. Copies published by the Free Software Foundation raise 33 funds for GNU development.--> 34<meta http-equiv="Content-Style-Type" content="text/css"> 35<style type="text/css"><!-- 36 pre.display { font-family:inherit } 37 pre.format { font-family:inherit } 38 pre.smalldisplay { font-family:inherit; font-size:smaller } 39 pre.smallformat { font-family:inherit; font-size:smaller } 40 pre.smallexample { font-size:smaller } 41 pre.smalllisp { font-size:smaller } 42 span.sc { font-variant:small-caps } 43 span.roman { font-family:serif; font-weight:normal; } 44 span.sansserif { font-family:sans-serif; font-weight:normal; } 45--></style> 46<link rel="stylesheet" type="text/css" href="../cs.css"> 47</head> 48<body> 49<div class="node"> 50<a name="Restricted-Pointers"></a> 51<p> 52Next: <a rel="next" accesskey="n" href="Vague-Linkage.html#Vague-Linkage">Vague Linkage</a>, 53Previous: <a rel="previous" accesskey="p" href="C_002b_002b-Volatiles.html#C_002b_002b-Volatiles">C++ Volatiles</a>, 54Up: <a rel="up" accesskey="u" href="C_002b_002b-Extensions.html#C_002b_002b-Extensions">C++ Extensions</a> 55<hr> 56</div> 57 58<h3 class="section">7.2 Restricting Pointer Aliasing</h3> 59 60<p><a name="index-restricted-pointers-3259"></a><a name="index-restricted-references-3260"></a><a name="index-restricted-this-pointer-3261"></a> 61As with the C front end, G++ understands the C99 feature of restricted pointers, 62specified with the <code>__restrict__</code>, or <code>__restrict</code> type 63qualifier. Because you cannot compile C++ by specifying the <samp><span class="option">-std=c99</span></samp> 64language flag, <code>restrict</code> is not a keyword in C++. 65 66 <p>In addition to allowing restricted pointers, you can specify restricted 67references, which indicate that the reference is not aliased in the local 68context. 69 70<pre class="smallexample"> void fn (int *__restrict__ rptr, int &__restrict__ rref) 71 { 72 /* <span class="roman">...</span> */ 73 } 74</pre> 75 <p class="noindent">In the body of <code>fn</code>, <var>rptr</var> points to an unaliased integer and 76<var>rref</var> refers to a (different) unaliased integer. 77 78 <p>You may also specify whether a member function's <var>this</var> pointer is 79unaliased by using <code>__restrict__</code> as a member function qualifier. 80 81<pre class="smallexample"> void T::fn () __restrict__ 82 { 83 /* <span class="roman">...</span> */ 84 } 85</pre> 86 <p class="noindent">Within the body of <code>T::fn</code>, <var>this</var> will have the effective 87definition <code>T *__restrict__ const this</code>. Notice that the 88interpretation of a <code>__restrict__</code> member function qualifier is 89different to that of <code>const</code> or <code>volatile</code> qualifier, in that it 90is applied to the pointer rather than the object. This is consistent with 91other compilers which implement restricted pointers. 92 93 <p>As with all outermost parameter qualifiers, <code>__restrict__</code> is 94ignored in function definition matching. This means you only need to 95specify <code>__restrict__</code> in a function definition, rather than 96in a function prototype as well. 97 98 </body></html> 99 100