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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. Hewlett-Packard Company makes no -- representations about the suitability of this software for any -- purpose. It is provided "as is" without express or implied warranty. -- --><Head><Title>swap</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>swap</H1><Table CellPadding=0 CellSpacing=0 width=100%><TR><TD Align=left><Img src = "algorithms.gif" Alt="" WIDTH = "194" HEIGHT = "38" ></TD><TD Align=right><Img src = "function.gif" Alt="" WIDTH = "194" HEIGHT = "38" ></TD></TR><TR><TD Align=left VAlign=top><b>Category</b>: algorithms</TD><TD Align=right VAlign=top><b>Component type</b>: function</TD></TR></Table><h3>Prototype</h3><pre>template <class <A href="Assignable.html">Assignable</A>> void swap(Assignable& a, Assignable& b);</pre> <h3>Description</h3>Assigns the contents of <tt>a</tt> to <tt>b</tt> and the contents of <tt>b</tt> to <tt>a</tt>.This is used as a primitive operation by many other algorithms.<h3>Definition</h3>Defined in the standard header <A href="algorithm">algorithm</A>, and in the nonstandardbackward-compatibility header <A href="algo.h">algo.h</A>.<h3>Requirements on types</h3><UL><LI>Assignable is a model of <A href="Assignable.html">Assignable</A>.</UL><h3>Preconditions</h3>None.<h3>Complexity</h3>Amortized constant time. <A href="#1">[1]</A> <A href="#2">[2]</A><h3>Example</h3><pre>int x = 1;int y = 2;assert(x == 1 && y == 2);swap(x, y);assert(x == 2 && y == 1);</pre><h3>Notes</h3><P><A name="1">[1]</A>The time required to <tt>swap</tt> two objects of type <tt>T</tt> willobviously depend on the type; "constant time" does not mean thatperformance will be the same for an 8-bit <tt>char</tt> as for a 128-bit<tt>complex<double></tt>. <P><A name="2">[2]</A>This implementation of <tt>swap</tt> makes one call to a copyconstructor and two calls to an assignment operator; roughly, then, itshould be expected to take about the same amount of time as threeassignments. In many cases, however, it is possible to write aspecialized version of <tt>swap</tt> that is far more efficient. Consider,for example, swapping two <tt><A href="Vector.html">vector</A><double></tt>s each of which has <tt>N</tt>elements. The unspecialized version requires <tt>3*N</tt> assignments of<tt>double</tt>, but a specialized version requires only ninepointer assignments. <b>This is important</b> because <tt>swap</tt> is used asa primitive operation in many other STL algorithms, and becausecontainers of containers (<tt><A href="List.html">list</A><<A href="Vector.html">vector</A><char> ></tt>, for example)are very common. The STL includes specialized versions of <tt>swap</tt> forall container classes. User-defined types should also providespecialized versions of <tt>swap</tt> whenever it is possible to write onethat is more efficient than the general version.<h3>See also</h3><tt><A href="iter_swap.html">iter_swap</A></tt>, <tt><A href="swap_ranges.html">swap_ranges</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> ?? 快捷鍵說明
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