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<html lang="en"><head><title>Using the GNU Compiler Collection (GCC)</title><meta http-equiv="Content-Type" content="text/html"><meta name="description" content="Using the GNU Compiler Collection (GCC)"><meta name="generator" content="makeinfo 4.6"><!--Copyright &copy; 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998,1999, 2000, 2001, 2002, 2003, 2004 Free Software Foundation, Inc.   <p>Permission is granted to copy, distribute and/or modify this documentunder the terms of the GNU Free Documentation License, Version 1.2 orany later version published by the Free Software Foundation; with theInvariant Sections being "GNU General Public License" and "FundingFree Software", the Front-Cover texts being (a) (see below), and withthe Back-Cover Texts being (b) (see below).  A copy of the license isincluded in the section entitled "GNU Free Documentation License".   <p>(a) The FSF's Front-Cover Text is:   <p>A GNU Manual   <p>(b) The FSF's Back-Cover Text is:   <p>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.--><meta http-equiv="Content-Style-Type" content="text/css"><style type="text/css"><!--  pre.display { font-family:inherit }  pre.format  { font-family:inherit }  pre.smalldisplay { font-family:inherit; font-size:smaller }  pre.smallformat  { font-family:inherit; font-size:smaller }  pre.smallexample { font-size:smaller }  pre.smalllisp    { font-size:smaller }--></style></head><body><div class="node"><p>Node:&nbsp;<a name="Restricted%20Pointers">Restricted Pointers</a>,Next:&nbsp;<a rel="next" accesskey="n" href="Vague-Linkage.html#Vague%20Linkage">Vague Linkage</a>,Previous:&nbsp;<a rel="previous" accesskey="p" href="Volatiles.html#Volatiles">Volatiles</a>,Up:&nbsp;<a rel="up" accesskey="u" href="C---Extensions.html#C++%20Extensions">C++ Extensions</a><hr><br></div><h3 class="section">Restricting Pointer Aliasing</h3><p>As with the C front end, G++ understands the C99 feature of restricted pointers,specified with the <code>__restrict__</code>, or <code>__restrict</code> typequalifier.  Because you cannot compile C++ by specifying the <code>-std=c99</code>language flag, <code>restrict</code> is not a keyword in C++.   <p>In addition to allowing restricted pointers, you can specify restrictedreferences, which indicate that the reference is not aliased in the localcontext.<pre class="smallexample">     void fn (int *__restrict__ rptr, int &amp;__restrict__ rref)     {       /* <small class="dots">...</small> */     }     </pre><p>In the body of <code>fn</code>, <var>rptr</var> points to an unaliased integer and<var>rref</var> refers to a (different) unaliased integer.   <p>You may also specify whether a member function's <var>this</var> pointer isunaliased by using <code>__restrict__</code> as a member function qualifier.<pre class="smallexample">     void T::fn () __restrict__     {       /* <small class="dots">...</small> */     }     </pre><p>Within the body of <code>T::fn</code>, <var>this</var> will have the effectivedefinition <code>T *__restrict__ const this</code>.  Notice that theinterpretation of a <code>__restrict__</code> member function qualifier isdifferent to that of <code>const</code> or <code>volatile</code> qualifier, in that itis applied to the pointer rather than the object.  This is consistent withother compilers which implement restricted pointers.   <p>As with all outermost parameter qualifiers, <code>__restrict__</code> isignored in function definition matching.  This means you only need tospecify <code>__restrict__</code> in a function definition, rather thanin a function prototype as well.   </body></html>
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