147 lines
6.5 KiB
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147 lines
6.5 KiB
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<HTML>
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<HEAD>
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<TITLE>equal()</TITLE>
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<LINK REL=StyleSheet HREF="../rw.css" TYPE="text/css" TITLE="Apache stdcxx Stylesheet"></HEAD>
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<A HREF="domain-error.html"><IMG SRC="images/bprev.gif" WIDTH=20 HEIGHT=21 ALT="Previous file" BORDER=O></A><A HREF="noframes.html"><IMG SRC="images/btop.gif" WIDTH=56 HEIGHT=21 ALT="Top of Document" BORDER=O></A><A HREF="booktoc.html"><IMG SRC="images/btoc.gif" WIDTH=56 HEIGHT=21 ALT="Contents" BORDER=O></A><A HREF="tindex.html"><IMG SRC="images/bindex.gif" WIDTH=56 HEIGHT=21 ALT="Index page" BORDER=O></A><A HREF="equal-range.html"><IMG SRC="images/bnext.gif" WIDTH=25 HEIGHT=21 ALT="Next file" BORDER=O></A><DIV CLASS="DOCUMENTNAME"><B>Apache C++ Standard Library Reference Guide</B></DIV>
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<H2>equal()</H2>
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<P><B>Library:</B> <A HREF="2-9.html">Algorithms</A></P>
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<PRE><HR><B><I>Function</I></B><HR></PRE>
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<UL>
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<LI><A HREF="#sec1">Local Index</A></LI>
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<LI><A HREF="#sec2">Summary</A></LI>
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<LI><A HREF="#sec3">Synopsis</A></LI>
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<LI><A HREF="#sec4">Description</A></LI>
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<LI><A HREF="#sec5">Complexity</A></LI>
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<LI><A HREF="#sec6">Example</A></LI>
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<LI><A HREF="#sec7">Standards Conformance</A></LI>
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</UL>
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<A NAME="sec1"><H3>Local Index</H3></A>
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No Entries
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<A NAME="sec2"><H3>Summary</H3></A>
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<P>Algorithm that compares two ranges of values for equality</P>
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<A NAME="sec3"><H3>Synopsis</H3></A>
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<PRE>#include <algorithm>
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namespace std {
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template <class InputIterator1, class InputIterator2>
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bool equal(InputIterator1 start1, InputIterator1 finish1,
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InputIterator2 start2);
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template <class InputIterator1, class InputIterator2,
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class BinaryPredicate>
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bool equal(InputIterator1 start1, InputIterator1 finish1,
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InputIterator2 start2, BinaryPredicate
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binary_pred);
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}
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</PRE>
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<A NAME="sec4"><H3>Description</H3></A>
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<P>The <SAMP>equal()</SAMP> algorithm does a pairwise comparison of all of the elements in one range with all of the elements in another range to see if they match. The first version of <SAMP>equal()</SAMP> uses <SAMP>operator==()</SAMP> as the comparison function, and the second version allows you to specify a binary predicate as the comparison function. The first version returns <SAMP>true</SAMP> if all of the corresponding elements are equal to each other. The second version of <SAMP>equal()</SAMP> returns <SAMP>true</SAMP> if for each pair of elements in the two ranges, the result of applying the binary predicate is true. In other words, <SAMP>equal()</SAMP> returns <SAMP>true</SAMP> if both of the following are true:</P>
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<UL>
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<LI><P CLASS="LIST">There are at least as many elements in the second range as in the first</P></LI>
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<LI><P CLASS="LIST">For every iterator <SAMP>i</SAMP> in the range <SAMP>[start1, finish1)</SAMP> the following corresponding conditions hold: </P></LI>
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<P CLASS="LIST"><SAMP>*i == *(start2 + (i - start1))</SAMP></P>
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<P CLASS="LIST">or</P>
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<P CLASS="LIST"><SAMP>binary_pred(*i, *(start2 + (i - start1))) == true</SAMP></P>
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</UL>
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<P>If one of these conditions is not true, <SAMP>equal()</SAMP> returns <SAMP>false</SAMP>.</P>
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<P>This algorithm assumes that all iterators in the range <SAMP>[start2, start2 + (finish1 - start1)]</SAMP> are dereferenceable.</P>
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<A NAME="sec5"><H3>Complexity</H3></A>
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<P><SAMP>equal()</SAMP> performs at most <SAMP>finish1 - start1</SAMP> comparisons or applications of the predicate.</P>
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<A NAME="sec6"><H3>Example</H3></A>
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<UL><PRE>//
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// equal.cpp
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//
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#include <algorithm> // equal
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#include <functional>
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#include <iostream>
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#include <vector>
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int main ()
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{
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// Typedef for convenience.
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typedef std::vector<int, std::allocator<int> > vector;
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typedef std::ostream_iterator <vector::value_type, char,
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std::char_traits<char> > os_iter;
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const vector::value_type a1[] = { 1, 2, 3, 4 };
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const vector::value_type a2[] = { 1, 2, 4, 3 };
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// Set up two vectors.
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const vector v1(a1, a1 + sizeof a1 / sizeof *a1);
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const vector v2(a2, a2 + sizeof a2 / sizeof *a2);
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// Check for equality.
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bool same = std::equal(v1.begin(), v1.end(),
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v2.begin());
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same = same && std::equal(v1.begin(), v1.end(),
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v2.begin(), std::equal_to<vector::value_type>());
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// Output the sequences.
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std::cout << "{ ";
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std::copy(v1.begin(), v1.end(), os_iter(std::cout, " "));
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std::cout << "} == { ";
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std::copy(v2.begin(), v2.end(), os_iter(std::cout, " "));
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// Output the result.
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std::cout << "} --> " << std::boolalpha
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<< same << std::endl;
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return 0;
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}
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Program Output
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</PRE></UL>
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<UL><PRE>{ 1 2 3 4 } == { 1 2 4 3 } --> false
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</PRE></UL>
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<A NAME="sec7"><H3>Standards Conformance</H3></A>
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<P><I>ISO/IEC 14882:1998 -- International Standard for Information Systems --Programming Language C++, Section 25.1.8</I></P>
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<BR>
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