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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>Bidirectional Iterator</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>Bidirectional Iterator</H1><Table CellPadding=0 CellSpacing=0 width=100%><TR><TD Align=left><Img src = "iterators.gif" Alt="" WIDTH = "194" HEIGHT = "38" ></TD><TD Align=right><Img src = "concept.gif" Alt="" WIDTH = "194" HEIGHT = "38" ></TD></TR><TR><TD Align=left VAlign=top><b>Category</b>: iterators</TD><TD Align=right VAlign=top><b>Component type</b>: concept</TD></TR></Table><h3>Description</h3>A Bidirectional Iterator is an iterator that can be both incrementedand decremented. The requirement that a Bidirectional Iteratorcan be decremented is the only thing that distinguishes Bidirectional Iterators from <A href="ForwardIterator.html">Forward Iterators</A>.<h3>Refinement of</h3><A href="ForwardIterator.html">Forward Iterator</A><h3>Associated types</h3>The same as for <A href="ForwardIterator.html">Forward Iterator</A>.<h3>Notation</h3><Table><TR><TD VAlign=top><tt>X</tt></TD><TD VAlign=top>A type that is a model of Bidirectional Iterator</TD></TR><TR><TD VAlign=top><tt>T</tt></TD><TD VAlign=top>The value type of <tt>X</tt></TD></TR><TR><TD VAlign=top><tt>i</tt>, <tt>j</tt></TD><TD VAlign=top>Object of type <tt>X</tt></TD></TR><TR><TD VAlign=top><tt>t</tt></TD><TD VAlign=top>Object of type <tt>T</tt></TD></tr></table><h3>Definitions</h3><h3>Valid expressions</h3>In addition to the expressions defined in <A href="ForwardIterator.html">Forward Iterator</A>, thefollowing expressions must be valid.<Table border><TR><TH>Name</TH><TH>Expression</TH><TH>Type requirements</TH><TH>Return type</TH></TR><TR><TD VAlign=top>Predecrement</TD><TD VAlign=top><tt>--i</tt></TD><TD VAlign=top> </TD><TD VAlign=top><tt>X&</tt></TD></TR><TR><TD VAlign=top>Postdecrement</TD><TD VAlign=top><tt>i--</tt></TD><TD VAlign=top> </TD><TD VAlign=top><tt>X</tt></TD></tr></table><h3>Expression Semantics</h3>Semantics of an expression is defined only where it is not defined in<A href="ForwardIterator.html">Forward Iterator</A>.<Table border><TR><TH>Name</TH><TH>Expression</TH><TH>Precondition</TH><TH>Semantics</TH><TH>Postcondition</TH></TR><TR><TD VAlign=top>Predecrement</TD><TD VAlign=top><tt>--i</tt></TD><TD VAlign=top><tt>i</tt> is dereferenceable or past-the-end. There exists a dereferenceable iterator <tt>j</tt> such that <tt>i == ++j</tt>.</TD><TD VAlign=top><tt>i</tt> is modified to point to the previous element.</TD><TD VAlign=top><tt>i</tt> is dereferenceable. <tt>&i = &--i</tt>. If <tt>i == j</tt>, then <tt>--i == --j</tt>. If <tt>j</tt> is dereferenceable and <tt>i == ++j</tt>, then <tt>--i == j</tt>.</TD></TR><TR><TD VAlign=top>Postdecrement</TD><TD VAlign=top><tt>i--</tt></TD><TD VAlign=top><tt>i</tt> is dereferenceable or past-the-end. There exists a dereferenceable iterator <tt>j</tt> such that <tt>i == ++j</tt>.</TD><TD VAlign=top>Equivalent to<pre>{ X tmp = i; --i; return tmp; }</pre></TD><TD VAlign=top> </TD></tr></table><h3>Complexity guarantees</h3>The complexity of operations on bidirectional iterators isguaranteed to be amortized constant time.<h3>Invariants</h3><Table border><TR><TD VAlign=top>Symmetry of increment and decrement</TD><TD VAlign=top>If <tt>i</tt> is dereferenceable, then <tt>++i; --i;</tt> is a null operation. Similarly, <tt>--i; ++i;</tt> is a null operation.</TD></tr></table><h3>Models</h3><UL><LI><tt>T*</tt><LI><tt><A href="List.html">list</A><T>::iterator</tt></UL><h3>Notes</h3><h3>See also</h3><A href="InputIterator.html">Input Iterator</A>, <A href="OutputIterator.html">Output Iterator</A>, <A href="ForwardIterator.html">Forward Iterator</A>,<A href="RandomAccessIterator.html">Random Access Iterator</A>, <A href="Iterators.html">Iterator overview</A><!--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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