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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>search_n</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>search_n</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>Search_n</tt> is an overloaded name; there are actually two <tt>search_n</tt>functions.<pre>template <class <A href="ForwardIterator.html">ForwardIterator</A>, class Integer, class T>ForwardIterator search_n(ForwardIterator first, ForwardIterator last, Integer count, const T& value);template <class <A href="ForwardIterator.html">ForwardIterator</A>, class Integer, class T, class <A href="BinaryPredicate.html">BinaryPredicate</A>>ForwardIterator search_n(ForwardIterator first, ForwardIterator last, Integer count, const T& value, BinaryPredicate binary_pred);</pre> <h3>Description</h3><tt>Search_n</tt> searches for a subsequence of <tt>count</tt> consecutive elements in the range <tt>[first, last)</tt>, all of which are equal to <tt>value</tt>. <A href="#1">[1]</A>It returns an iterator pointing to the beginning of that subsequence,or else <tt>last</tt> if no such subsequence exists. The two versions of <tt>search_n</tt> differ in how they determine whether two elements are the same:the first uses <tt>operator==</tt>, and the second uses the user-supplied<A href="functors.html">function object</A> <tt>binary_pred</tt>.<P>The first version of <tt>search</tt> returns the first iterator <tt>i</tt> in therange <tt>[first, last - count)</tt> <A href="#2">[2]</A> such that, for every iterator <tt>j</tt> inthe range <tt>[i, i + count)</tt>, <tt>*j == value</tt>. The second version returns the first iterator <tt>i</tt> in therange <tt>[first, last - count)</tt> such that, for every iterator <tt>j</tt> inthe range <tt>[i, i + count)</tt>, <tt>binary_pred(*j, value)</tt> is <tt>true</tt>.<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>For the first version:<UL><LI><tt>ForwardIterator</tt> is a model of <A href="ForwardIterator.html">Forward Iterator</A>.<LI><tt>Integer</tt> is an integral type.<LI><tt>T</tt> is a model of <A href="EqualityComparable.html">EqualityComparable</A>.<LI><tt>ForwardIterator</tt>'s value type is a model of <A href="EqualityComparable.html">EqualityComparable</A>.<LI>Objects of <tt>ForwardIterator</tt>'s value type can be compared for equality with Objects of type <tt>T</tt>.</UL>For the first version:<UL><LI><tt>ForwardIterator</tt> is a model of <A href="ForwardIterator.html">Forward Iterator</A>.<LI><tt>Integer</tt> is an integral type.<LI><tt>T</tt> is a model of <A href="EqualityComparable.html">EqualityComparable</A>.<LI><tt>BinaryPredicate</tt> is a model of <A href="BinaryPredicate.html">Binary Predicate</A>.<LI><tt>ForwardIterator</tt>'s value type is convertible to <tt>BinaryPredicate</tt>'s first argument type.<LI><tt>T</tt> is convertible to <tt>BinaryPredicate</tt>'s second argument type.</UL><h3>Preconditions</h3><UL><LI><tt>[first, last)</tt> is a valid range.<LI><tt>count</tt> is non-negative <A href="#1">[1]</A>.</UL><h3>Complexity</h3>Linear. <tt>Search_n</tt> performs at most <tt>last - first</tt> comparisons.<P>(The C++ standard permits the complexity to be <i>O</i>(<tt>n</tt> (<tt>last</tt> - <tt>first</tt>)),but this is unnecessarily lax. There is no reason for <tt>search_n</tt> toexamine any element more than once.)<h3>Example</h3><pre>bool eq_nosign(int x, int y) { return abs(x) == abs(y); }void lookup(int* first, int* last, size_t count, int val) { cout << "Searching for a sequence of " << count << " '" << val << "'" << (count != 1 ? "s: " : ": "); int* result = search_n(first, last, count, val); if (result == last) cout << "Not found" << endl; else cout << "Index = " << result - first << endl;}void lookup_nosign(int* first, int* last, size_t count, int val) { cout << "Searching for a (sign-insensitive) sequence of " << count << " '" << val << "'" << (count != 1 ? "s: " : ": "); int* result = search_n(first, last, count, val, eq_nosign); if (result == last) cout << "Not found" << endl; else cout << "Index = " << result - first << endl;}int main() { const int N = 10; int A[N] = {1, 2, 1, 1, 3, -3, 1, 1, 1, 1}; lookup(A, A+N, 1, 4); lookup(A, A+N, 0, 4); lookup(A, A+N, 1, 1); lookup(A, A+N, 2, 1); lookup(A, A+N, 3, 1); lookup(A, A+N, 4, 1); lookup(A, A+N, 1, 3); lookup(A, A+N, 2, 3); lookup_nosign(A, A+N, 1, 3); lookup_nosign(A, A+N, 2, 3);}</pre><P>The output is<pre>Searching for a sequence of 1 '4': Not foundSearching for a sequence of 0 '4's: Index = 0Searching for a sequence of 1 '1': Index = 0Searching for a sequence of 2 '1's: Index = 2Searching for a sequence of 3 '1's: Index = 6Searching for a sequence of 4 '1's: Index = 6Searching for a sequence of 1 '3': Index = 4Searching for a sequence of 2 '3's: Not foundSearching for a (sign-insensitive) sequence of 1 '3': Index = 4Searching for a (sign-insensitive) sequence of 2 '3's: Index = 4</pre><h3>Notes</h3><P><A name="1">[1]</A>Note that <tt>count</tt> is permitted to be zero: a subsequence of zeroelements is well defined. If you call <tt>search_n</tt> with <tt>count</tt> equalto zero, then the search will always succeed: no matter what <tt>value</tt>is, every range contains a subrange of zero consecutive elements thatare equal to <tt>value</tt>. When <tt>search_n</tt> is called with <tt>count</tt> equal tozero, the return value is always <tt>first</tt>.<P><A name="2">[2]</A>The reason that this range is <tt>[first, last - count)</tt>, rather thanjust <tt>[first, last)</tt>, is that we are looking for a subsequence whoselength is <tt>count</tt>; an iterator <tt>i</tt> can't be the beginning of such asubsequence unless <tt>last - count</tt> is greater than or equal to <tt>count</tt>.Note the implication of this: you may call <tt>search_n</tt> with argumentssuch that <tt>last - first</tt> is less than <tt>count</tt>, but such a search willalways fail.<h3>See also</h3><tt><A href="search.html">search</A></tt>, <tt><A href="find_end.html">find_end</A></tt>, <tt><A href="find.html">find</A></tt>, <tt><A href="find_if.html">find_if</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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