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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>select1st<Pair></Title><!-- Generated by htmldoc --></HEAD><BODY BGCOLOR="#ffffff" LINK="#0000ee" TEXT="#000000" VLINK="#551a8b" ALINK="#ff0000"> <IMG SRC="CorpID.gif" ALT="SGI" HEIGHT="43" WIDTH="151"> <!--end header--><BR Clear><H1>select1st<Pair></H1><Table CellPadding=0 CellSpacing=0 width=100%><TR><TD Align=left><Img src = "functors.gif" Alt="" WIDTH = "194" HEIGHT = "38" ></TD><TD Align=right><Img src = "type.gif" Alt="" WIDTH = "194" HEIGHT = "39" ></TD></TR><TR><TD Align=left VAlign=top><b>Category</b>: functors</TD><TD Align=right VAlign=top><b>Component type</b>: type</TD></TR></Table><h3>Description</h3><tt>Select1st</tt> is a <A href="functors.html">function object</A> that takes a single argument, a <tt><A href="pair.html">pair</A></tt> <A href="#1">[1]</A>, and returns the pair's first element.<h3>Example</h3>Print all of a <tt><A href="Map.html">map</A></tt>'s keys.<pre>int main(){ <A href="Map.html">map</A><int, double> M; M[1] = 0.3; M[47] = 0.8; M[33] = 0.1; <A href="transform.html">transform</A>(M.begin(), M.end(), <A href="ostream_iterator.html">ostream_iterator</A><int>(cout, " "), select1st<<A href="Map.html">map</A><int, double>::value_type>()); // The output is 1 33 47.}</pre><h3>Definition</h3>Defined in the standard header <A href="functional">functional</A>, and in the nonstandardbackward-compatibility header <A href="function.h">function.h</A>.This function object 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>Pair</tt></TD><TD VAlign=top>The function object's argument type.</TD><TD VAlign=top> </TD></tr></table><h3>Model of</h3><A href="AdaptableUnaryFunction.html">Adaptable Unary Function</A><A href="AdaptableUnaryFunction.html">Adaptable Unary Function</A><A href="AdaptableUnaryFunction.html">Adaptable Unary Function</A><h3>Type requirements</h3>There exist some types <tt>U</tt> and <tt>V</tt> such that <tt>Pair</tt> provides the sameinterface as a <tt><A href="pair.html">pair</A><U,V></tt>. <A href="#1">[1]</A><h3>Public base classes</h3><tt><A href="unary_function.html">unary_function</A><Pair, Pair::first_type></tt><h3>Members</h3><Table border><TR><TH>Member</TH><TH>Where defined</TH><TH>Description</TH></TR><TR><TD VAlign=top><tt>argument_type</tt></TD><TD VAlign=top> <A href="AdaptableUnaryFunction.html">Adaptable Unary Function</A></TD><TD VAlign=top>The type of <tt>select1st</tt>'s argument: <tt>Pair</tt></TD></TR><TR><TD VAlign=top><tt>result_type</tt></TD><TD VAlign=top> <A href="AdaptableUnaryFunction.html">Adaptable Unary Function</A></TD><TD VAlign=top>The type of the result: <tt>Pair::first_type</tt></TD></TR><TR><TD VAlign=top><pre>const Pair::first_type&operator()(const Pair& p) const</pre></TD><TD VAlign=top> <A href="AdaptableUnaryFunction.html">Adaptable Unary Function</A></TD><TD VAlign=top>Function call. The return value is <tt>p.first</tt>.</TD></tr></table><h3>New members</h3>All of <tt>select1st</tt>'s members are defined in the <A href="AdaptableUnaryFunction.html">Adaptable Unary Function</A>requirements. <tt>Select1st</tt> does not introduce any new members.<h3>Notes</h3><P><A name="1">[1]</A><tt>Pair</tt> is not actually required to be a <tt><A href="pair.html">pair</A><U,V></tt>, butmerely to support the same interface as <tt><A href="pair.html">pair</A></tt>. In almost all cases the template parameter will be a <tt><A href="pair.html">pair</A></tt>, but it is occasionally useful for it to be something else. One example is a <tt>struct</tt> thathas the members <tt>first</tt>, <tt>second</tt>, and <tt>third</tt>.<h3>See also</h3><tt><A href="identity.html">identity</A></tt>, <tt><A href="select2nd.html">select2nd</A></tt>, <tt><A href="project1st.html">project1st</A></tt>, <tt><A href="project2nd.html">project2nd</A></tt><!--start footer--> <HR SIZE="6"><A href="http://www.sgi.com/"><IMG SRC="surf.gif" HEIGHT="54" WIDTH="54" ALT="[Silicon Surf]"></A><A HREF="index.html"><IMG SRC="stl_home.gif" HEIGHT="54" WIDTH="54" ALT="[STL Home]"></A><BR><FONT SIZE="-2"><A href="http://www.sgi.com/Misc/sgi_info.html" TARGET="_top">Copyright © 1999 Silicon Graphics, Inc.</A> All Rights Reserved.</FONT><FONT SIZE="-3"><a href="http://www.sgi.com/Misc/external.list.html" TARGET="_top">TrademarkInformation</A></FONT><P></BODY></HTML> ?? 快捷鍵說(shuō)明
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