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copied!<p>gcc uses <code>__attribute__(( <attr> ))</code> to define <a href="http://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html" rel="nofollow">extra attributes</a> on functions.</p> <ul> <li><p><strong>pure</strong>: only accesses (but does not modify) parameters and global memory. GCC uses this information to determine if the optimizer can completely omit repeated calls to the function (local-memoization). Two notable pure functions are <code>strlen</code> and <code>memcmp</code>.</p></li> <li><p><strong>const</strong>: not to be confused with C++ const, const functions only accesses parameters and those parameters must not be pointers. It is basically a more restricted version of <code>pure</code>. The optimizer treats <code>const</code> functions that same as <code>pure</code>. Though in theory it could perform more aggressive (non-local) memoization than it does for <code>pure</code>.</p></li> </ul> <p>C++11's new attribute syntax (§7.6) was designed to do just this sort of thing. Currently you cannot use C++'s attribute syntax to set GCC attributes, but that will change in future gcc versions.</p> <p>So you will be able to assign the <code>pure</code> attribute to functions using the attribute syntax. But there isn't a standard <code>pure</code> attribute. pure will be compiler specific, but it will do the right thing on gcc.</p> <p>For the curious, here is the list of the standard attributes:</p> <ul> <li>align</li> <li>noreturn</li> <li><strike>override</strike></li> <li><strike>hiding</strike></li> <li><strike>base_check</strike></li> <li>carries_dependency</li> </ul>

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