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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>accumulate</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>accumulate</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><tt>Accumulate</tt> is an overloaded name; there are actually two <tt>accumulate</tt>functions.<pre>template <class <A href="InputIterator.html">InputIterator</A>, class T>T accumulate(InputIterator first, InputIterator last, T init);template <class <A href="InputIterator.html">InputIterator</A>, class T, class <A href="BinaryFunction.html">BinaryFunction</A>>T accumulate(InputIterator first, InputIterator last, T init, BinaryFunction binary_op);</pre> <h3>Description</h3><tt>Accumulate</tt> is a generalization of summation: it computes the sum(or some other binary operation) of <tt>init</tt> and all of the elementsin the range <tt>[first, last)</tt>. <A href="#1">[1]</A> <P>The <A href="functors.html">function object</A> <tt>binary_op</tt> is not required to be eithercommutative or associative: the order of all of <tt>accumulate</tt>'s operationsis specified. The result is first initialized to <tt>init</tt>. Then, for eachiterator <tt>i</tt> in <tt>[first, last)</tt>, in order from beginning to end,it is updated by <tt>result = result + *i</tt> (in the first version) or<tt>result = binary_op(result, *i)</tt> (in the second version).<h3>Definition</h3>Defined in the standard header <A href="numeric">numeric</A>, and in the nonstandardbackward-compatibility header <A href="algo.h">algo.h</A>.<h3>Requirements on types</h3>For the first version, the one that takes two arguments:<UL><LI><tt>InputIterator</tt> is a model of <A href="InputIterator.html">Input Iterator</A>.<LI><tt>T</tt> is a model of <A href="Assignable.html">Assignable</A>.<LI>If <tt>x</tt> is an object of type <tt>T</tt> and <tt>y</tt> is an object of <tt>InputIterator</tt>'s value type, then <tt>x + y</tt> is defined.<LI>The return type of <tt>x + y</tt> is convertible to <tt>T</tt>.</UL>For the second version, the one that takes three arguments:<UL><LI><tt>InputIterator</tt> is a model of <A href="InputIterator.html">Input Iterator</A>.<LI><tt>T</tt> is a model of <A href="Assignable.html">Assignable</A>.<LI><tt>BinaryFunction</tt> is a model of <A href="BinaryFunction.html">Binary Function</A>.<LI><tt>T</tt> is convertible to <tt>BinaryFunction</tt>'s first argument type.<LI>The value type of <tt>InputIterator</tt> is convertible to <tt>BinaryFunction</tt>'s second argument type.<LI><tt>BinaryFunction</tt>'s return type is convertible to <tt>T</tt>.</UL><h3>Preconditions</h3><UL><LI><tt>[first, last)</tt> is a valid range.</UL><h3>Complexity</h3>Linear. Exactly <tt>last - first</tt> invocations of the binary operation.<h3>Example</h3><pre>int main(){ int A[] = {1, 2, 3, 4, 5}; const int N = sizeof(A) / sizeof(int); cout << "The sum of all elements in A is " << accumulate(A, A + N, 0) << endl; cout << "The product of all elements in A is " << accumulate(A, A + N, 1, multiplies<int>()) << endl;}</pre><h3>Notes</h3><P><A name="1">[1]</A>There are several reasons why it is important that <tt>accumulate</tt>starts with the value <tt>init</tt>. One of the most basic is that thisallows <tt>accumulate</tt> to have a well-defined result even if <tt>[first,last)</tt> is an empty range: if it is empty, the return value is <tt>init</tt>.If you want to find the sum of all of the elements in <tt>[first, last)</tt>,you can just pass <tt>0</tt> as <tt>init</tt>.<h3>See also</h3><tt><A href="inner_product.html">inner_product</A></tt>, <tt><A href="partial_sum.html">partial_sum</A></tt>, <tt><A href="adjacent_difference.html">adjacent_difference</A></tt>,<tt><A href="count.html">count</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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