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<HTML><!-- -- Copyright (c) 1996-1999 -- Silicon Graphics Computer Systems, Inc. -- -- Permission to use, copy, modify, distribute and sell this software -- and its documentation for any purpose is hereby granted without fee, -- provided that the above copyright notice appears in all copies and -- that both that copyright notice and this permission notice appear -- in supporting documentation. Silicon Graphics makes no -- representations about the suitability of this software for any -- purpose. It is provided "as is" without express or implied warranty. -- -- Copyright (c) 1994 -- Hewlett-Packard Company -- -- Permission to use, copy, modify, distribute and sell this software -- and its documentation for any purpose is hereby granted without fee, -- provided that the above copyright notice appears in all copies and -- that both that copyright notice and this permission notice appear -- in supporting documentation. 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It is provided "as is" without express or implied warranty. -- --><Head><Title>hash<T></Title><!-- Generated by htmldoc --></HEAD><BODY TEXT="#000000" LINK="#006600" ALINK="#003300" VLINK="#7C7F87" BGCOLOR="#FFFFFF"><A HREF="/"><IMG SRC="/images/common/sgilogo_small.gif" ALT="SGI Logo" WIDTH="80" HEIGHT="72" BORDER="0"></A><P><!--end header--><BR Clear><H1>hash<T></H1><Table CellPadding=0 CellSpacing=0 width=100%><TR><TD Align=left><Img src = "containers.gif" Alt="" WIDTH = "194" HEIGHT = "38" ></TD><TD Align=right><Img src = "type.gif" Alt="" WIDTH = "194" HEIGHT = "38" ></TD></TR><TR><TD Align=left><Img src = "functors.gif" Alt="" WIDTH = "194" HEIGHT = "38" ></TD><TD Align=right></TD></TR><TR><TD Align=left VAlign=top><b>Categories</b>: containers, functors</TD><TD Align=right VAlign=top><b>Component type</b>: type</TD></TR></Table><h3>Description</h3>The function object <tt>hash<T></tt> is a <A href="HashFunction.html">Hash Function</A>; it is used asthe default hash function by all of the <A href="HashedAssociativeContainer.html">Hashed AssociativeContainers</A> that are included in the STL.<P>The <tt>hash<T></tt> template is only defined for template arguments of type<tt>char*</tt>, <tt>const char*</tt>, <tt><A href="Rope.html">crope</A></tt>, <tt><A href="Rope.html">wrope</A></tt>, and the built-inintegral types. <A href="#1">[1]</A> If you need a Hash Function with a differentargument type, you must either provide your own templatespecialization or else use a different Hash Function.<h3>Example</h3><pre>int main(){ hash<const char*> H; cout << "foo -> " << H("foo") << endl; cout << "bar -> " << H("bar") << endl;}</pre><h3>Definition</h3>Defined in the headers <A href="hash_map">hash_map</A> and <A href="hash_set">hash_set</A>, and in thebackward-compatibility headers <A href="hash_map.h">hash_map.h</A> and <A href="hash_set.h">hash_set.h</A>.This class is an SGI extension; it is not part of the C++ standard.<h3>Template parameters</h3><Table border><TR><TH>Parameter</TH><TH>Description</TH><TH>Default</TH></TR><TR><TD VAlign=top><tt>T</tt></TD><TD VAlign=top>The argument type. That is, the type of object that is being hashed. </TD><TD VAlign=top> </TD></tr></table><h3>Model of</h3><A href="HashFunction.html">Hash Function</A><h3>Type requirements</h3><tt>T</tt> must be a type for which a specialization of <tt>hash</tt> has beendefined. The STL defines the following specializations: <UL><LI><tt>char*</tt><LI><tt>const char*</tt><LI><tt><A href="Rope.html">crope</A></tt><LI><tt><A href="Rope.html">wrope</A></tt><LI><tt>char</tt><LI><tt>signed char</tt><LI><tt>unsigned char</tt><LI><tt>short</tt><LI><tt>unsigned short</tt><LI><tt>int</tt><LI><tt>unsigned int</tt><LI><tt>long</tt><LI><tt>unsigned long</tt></UL><h3>Public base classes</h3>None.<h3>Members</h3><Table border><TR><TH>Member</TH><TH>Where defined</TH><TH>Description</TH></TR><TR><TD VAlign=top><tt>size_t operator()(const T& x)</tt></TD><TD VAlign=top> <A href="HashFunction.html">Hash Function</A></TD><TD VAlign=top>Returns <tt>x</tt>'s hash value.</TD></tr></table><h3>New members</h3>All of <tt>hash</tt>'s members are defined in the <A href="HashFunction.html">Hash Function</A>requirements. <tt>Hash</tt> does not introduce any new members.<h3>Notes</h3><P><A name="1">[1]</A>Technically, what this means is that the actual template<tt>hash<T></tt> is an empty class; the member function <tt>operator()</tt> is defined only in the various specializations.<h3>See also</h3><A href="HashedAssociativeContainer.html">Hashed Associative Container</A>, <A href="HashFunction.html">Hash Function</A><!-- start footer --><!-- Footer Begins --><STYLE TYPE="text/css"><!--TD.footer, TD.footer A{ font-family: Arial, helvetica, sans-serif; font-size: 8pt;}A.home {font-family: Arial, helvetica, sans-serif;}--></STYLE><P><A CLASS="home" HREF="index.html">STL Home</A><P><TABLE WIDTH="600" CELLPADDING="0" CELLPADDING="0" BORDER="0"> <TR> <TD ALIGN="RIGHT" CLASS="footer"><A HREF="/company_info/terms.html" TARGET="_top">terms of use</A> | <A HREF="/company_info/privacy.html" TARGET="_top">privacy policy</A></TD> <TD ALIGN="CENTER" CLASS="footer"> | </TD> <TD ALIGN="LEFT" CLASS="footer"><A HREF="/cgi-bin/feedback/" TARGET="_top">contact us</A></TD> </TR><TR> <TD ALIGN="RIGHT" CLASS="footer">Copyright © 1993-2003 Silicon Graphics, Inc. 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