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It is provided "as is" without express or implied warranty. -- --><Head><Title>equal_range</Title><!-- Generated by htmldoc --></HEAD><BODY TEXT="#000000" LINK="#006600" ALINK="#003300" VLINK="#7C7F87" BGCOLOR="#FFFFFF"><A HREF="/"><IMG SRC="/images/common/sgilogo_small.gif" ALT="SGI Logo" WIDTH="80" HEIGHT="72" BORDER="0"></A><P><!--end header--><BR Clear><H1>equal_range</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>Equal_range</tt> is an overloaded name; there are actually two <tt>equal_range</tt>functions.<pre>template <class <A href="ForwardIterator.html">ForwardIterator</A>, class <A href="LessThanComparable.html">LessThanComparable</A>><A href="pair.html">pair</A><ForwardIterator, ForwardIterator>equal_range(ForwardIterator first, ForwardIterator last, const LessThanComparable& value);template <class <A href="ForwardIterator.html">ForwardIterator</A>, class T, class <A href="StrictWeakOrdering.html">StrictWeakOrdering</A>><A href="pair.html">pair</A><ForwardIterator, ForwardIterator>equal_range(ForwardIterator first, ForwardIterator last, const T& value, StrictWeakOrdering comp);</pre> <h3>Description</h3><tt>Equal_range</tt> is a version of binary search: it attempts to find theelement <tt>value</tt> in an ordered range <tt>[first, last)</tt> <A href="#1">[1]</A>. Thevalue returned by <tt>equal_range</tt> is essentially a combination ofthe values returned by <tt><A href="lower_bound.html">lower_bound</A></tt> and <tt><A href="upper_bound.html">upper_bound</A></tt>:it returns a pair of iterators <tt>i</tt> and <tt>j</tt> such that <tt>i</tt> is the first position where <tt>value</tt> could be inserted without violatingthe ordering and <tt>j</tt> is the last position where <tt>value</tt> could beinserted without violating the ordering. It follows that everyelement in the range <tt>[i, j)</tt> is equivalent to <A href="#1">[1]</A> <tt>value</tt>, and that<tt>[i, j)</tt> is the largest subrange of <tt>[first, last)</tt> that has thisproperty. The first version of <tt>equal_range</tt>uses <tt>operator<</tt> for comparison, and the second uses the <A href="functors.html">function object</A> <tt>comp</tt>.<P>The first version of <tt>equal_range</tt> returns a pair of iterators <tt>[i, j)</tt>.<tt>i</tt> is the furthermost iterator in <tt>[first, last)</tt> such that, forevery iterator <tt>k</tt> in <tt>[first, i)</tt>, <tt>*k < value</tt>. <tt>j</tt> is thefurthermost iterator in <tt>[first, last)</tt> such that, for every iterator<tt>k</tt> in <tt>[first, j)</tt>, <tt>value < *k</tt> is <tt>false</tt>. For every iterator <tt>k</tt> in <tt>[i, j)</tt>, neither <tt>value < *k</tt> nor <tt>*k < value</tt> is <tt>true</tt>. <A href="#2">[2]</A><P>The second version of <tt>equal_range</tt> returns a pair of iterators <tt>[i,j)</tt>. <tt>i</tt> is the furthermost iterator in <tt>[first, last)</tt> such that,for every iterator <tt>k</tt> in <tt>[first, i)</tt>, <tt>comp(*k, value)</tt> is <tt>true</tt>.<tt>j</tt> is the furthermost iterator in <tt>[first, last)</tt> such that, forevery iterator <tt>k</tt> in <tt>[first, j)</tt>, <tt>comp(value, *k)</tt> is <tt>false</tt>. Forevery iterator <tt>k</tt> in <tt>[i, j)</tt>, neither <tt>comp(value, *k)</tt> nor<tt>comp(*k, value)</tt> is <tt>true</tt>. <A href="#2">[2]</A><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>LessThanComparable</tt> is a model of <A href="LessThanComparable.html">LessThan Comparable</A>.<LI>The ordering on objects of type <tt>LessThanComparable</tt> is a <i>strict weak ordering</i>, as defined in the <A href="LessThanComparable.html">LessThan Comparable</A> requirements.<LI><tt>ForwardIterator</tt>'s value type is the same type as <tt>LessThanComparable</tt>.</UL>For the second version:<UL><LI><tt>ForwardIterator</tt> is a model of <A href="ForwardIterator.html">Forward Iterator</A>.<LI><tt>StrictWeakOrdering</tt> is a model of <A href="StrictWeakOrdering.html">Strict Weak Ordering</A>.<LI><tt>ForwardIterator</tt>'s value type is the same type as <tt>T</tt>.<LI><tt>ForwardIterator</tt>'s value type is convertible to <tt>StrictWeakOrdering</tt>'s argument type.</UL><h3>Preconditions</h3>For the first version:<UL><LI><tt>[first, last)</tt> is a valid range.<LI><tt>[first, last)</tt> is ordered in ascending order according to <tt>operator<</tt>. That is, for every pair of iterators <tt>i</tt> and <tt>j</tt> in <tt>[first, last)</tt> such that <tt>i</tt> precedes <tt>j</tt>, <tt>*j < *i</tt> is <tt>false</tt>.</UL>For the second version:<UL><LI><tt>[first, last)</tt> is a valid range.<LI><tt>[first, last)</tt> is ordered in ascending order according to the <A href="functors.html">function object</A> <tt>comp</tt>. That is, for every pair of iterators <tt>i</tt> and <tt>j</tt> in <tt>[first, last)</tt> such that <tt>i</tt> precedes <tt>j</tt>, <tt>comp(*j, *i)</tt> is <tt>false</tt>.</UL><h3>Complexity</h3>The number of comparisons is logarithmic: at most <tt>2 * log(last - first) +1</tt>. If <tt>ForwardIterator</tt> is a <A href="RandomAccessIterator.html">Random Access Iterator</A> then thenumber of steps through the range is also logarithmic; otherwise, the number of steps is proportional to <tt>last - first</tt>. <A href="#3">[3]</A><h3>Example</h3><pre>int main(){ int A[] = { 1, 2, 3, 3, 3, 5, 8 }; const int N = sizeof(A) / sizeof(int); for (int i = 2; i <= 4; ++i) { pair<int*, int*> result = equal_range(A, A + N, i); cout << endl; cout << "Searching for " << i << endl; cout << " First position where " << i << " could be inserted: " << result.first - A << endl; cout << " Last position where " << i << " could be inserted: " << result.second - A << endl; if (result.first < A + N) cout << " *result.first = " << *result.first << endl; if (result.second < A + N) cout << " *result.second = " << *result.second << endl; }} </pre>The output is:<pre>Searching for 2 First position where 2 could be inserted: 1 Last position where 2 could be inserted: 2 *result.first = 2 *result.second = 3Searching for 3 First position where 3 could be inserted: 2 Last position where 3 could be inserted: 5 *result.first = 3 *result.second = 5Searching for 4 First position where 4 could be inserted: 5 Last position where 4 could be inserted: 5 *result.first = 5 *result.second = 5</pre><h3>Notes</h3><P><A name="1">[1]</A>Note that you may use an ordering that is a strict weak orderingbut not a total ordering; that is, there might be values <tt>x</tt> and <tt>y</tt>such that <tt>x < y</tt>, <tt>x > y</tt>, and <tt>x == y</tt> are all <tt>false</tt>. (See the<A href="LessThanComparable.html">LessThan Comparable</A> requirements for a more complete discussion.)Finding <tt>value</tt> in the range <tt>[first, last)</tt>, then, doesn't meanfinding an element that is equal to <tt>value</tt> but rather one that is<i>equivalent to</i> <tt>value</tt>: one that is neither greater than nor lessthan <tt>value</tt>. If you're using a total ordering, however (if you'reusing <tt>strcmp</tt>, for example, or if you're using ordinary arithmeticcomparison on integers), then you can ignore this technicaldistinction: for a total ordering, equality and equivalence arethe same.<P><A name="2">[2]</A>Note that <tt>equal_range</tt> may return an empty range; that is, itmay return a pair both of whose elements are the same iterator.<tt>Equal_range</tt> returns an empty range if and only if the range <tt>[first,last)</tt> contains no elements equivalent to <tt>value</tt>. In this case itfollows that there is only one position where <tt>value</tt> could beinserted without violating the range's ordering, so the return valueis a pair both of whose elements are iterators that point to thatposition.<P><A name="3">[3]</A>This difference between <A href="RandomAccessIterator.html">Random Access Iterators</A> and<A href="ForwardIterator.html">Forward Iterators</A> is simply because <tt><A href="advance.html">advance</A></tt> is constanttime for <A href="RandomAccessIterator.html">Random Access Iterators</A> and linear time for <A href="ForwardIterator.html">Forward Iterators</A>.<h3>See also</h3><tt><A href="lower_bound.html">lower_bound</A></tt>, <tt><A href="upper_bound.html">upper_bound</A></tt>, <tt><A href="binary_search.html">binary_search</A></tt><!-- start footer --><!-- Footer Begins --><STYLE TYPE="text/css"><!--TD.footer, TD.footer A{ font-family: Arial, helvetica, sans-serif; font-size: 8pt;}A.home {font-family: Arial, helvetica, sans-serif;}--></STYLE><P><A CLASS="home" HREF="index.html">STL Home</A><P><TABLE WIDTH="600" CELLPADDING="0" CELLPADDING="0" BORDER="0"> <TR> <TD ALIGN="RIGHT" CLASS="footer"><A HREF="/company_info/terms.html" TARGET="_top">terms of use</A> | <A HREF="/company_info/privacy.html" TARGET="_top">privacy policy</A></TD> <TD ALIGN="CENTER" CLASS="footer"> | </TD> <TD ALIGN="LEFT" CLASS="footer"><A HREF="/cgi-bin/feedback/" TARGET="_top">contact us</A></TD> </TR><TR> <TD ALIGN="RIGHT" CLASS="footer">Copyright © 1993-2003 Silicon Graphics, Inc. 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