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| <TITLE>lexicographical_compare()</TITLE> |
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| <H2>lexicographical_compare()</H2> |
| <P><B>Library:</B> <A HREF="2-9.html">Algorithms</A></P> |
| |
| <PRE><HR><B><I>Function</I></B><HR></PRE> |
| |
| <UL> |
| <LI><A HREF="#sec1">Local Index</A></LI> |
| <LI><A HREF="#sec2">Summary</A></LI> |
| <LI><A HREF="#sec3">Synopsis</A></LI> |
| <LI><A HREF="#sec4">Description</A></LI> |
| <LI><A HREF="#sec5">Complexity</A></LI> |
| <LI><A HREF="#sec6">Example</A></LI> |
| <LI><A HREF="#sec7">Standards Conformance</A></LI> |
| </UL> |
| <A NAME="sec1"><H3>Local Index</H3></A> |
| No Entries |
| <A NAME="sec2"><H3>Summary</H3></A> |
| <P>Algorithm that returns <SAMP>true</SAMP> if one sequence compares lexicographically less than another, <SAMP>false</SAMP> otherwise</P> |
| <A NAME="sec3"><H3>Synopsis</H3></A> |
| |
| <PRE>#include <algorithm> |
| |
| namespace std { |
| template <class InputIterator1, class InputIterator2> |
| bool |
| lexicographical_compare(InputIterator1 start1, |
| InputIterator1 finish1, |
| InputIterator2 start2, |
| InputIterator2 finish2); |
| |
| template <class InputIterator1, class InputIterator2, |
| class Compare> |
| bool |
| lexicographical_compare(InputIterator1 start1, |
| InputIterator1 finish1, |
| InputIterator2 start2, |
| InputIterator2 finish2, |
| Compare comp); |
| } |
| </PRE> |
| <A NAME="sec4"><H3>Description</H3></A> |
| <P>The <SAMP>lexicographical_compare()</SAMP> functions compare each element in the range <SAMP>[start1, finish1)</SAMP> to the corresponding element in the range <SAMP>[start2, finish2)</SAMP> using iterators <SAMP>i</SAMP> and <SAMP>j</SAMP>. </P> |
| <P>The first version of the algorithm uses <SAMP>operator<()</SAMP> as the default comparison operator. It immediately returns <SAMP>true</SAMP> if it encounters any pair in which <SAMP>*i</SAMP> is less than <SAMP>*j</SAMP>, and immediately returns <SAMP>false</SAMP> if <SAMP>*j</SAMP> is less than <SAMP>*i</SAMP>. If the algorithm reaches the end of the first sequence before reaching the end of the second sequence, it also returns <SAMP>true</SAMP>. </P> |
| <P>The second version of the function takes an argument <SAMP>comp</SAMP> that defines a comparison function that is used in place of the default <SAMP>operator<()</SAMP>.</P> |
| <P>The <SAMP>lexicographical_compare()</SAMP> functions can be used with all the data types included in the standard library.</P> |
| <A NAME="sec5"><H3>Complexity</H3></A> |
| <P><SAMP>lexicographical_compare()</SAMP> performs at most <SAMP>min((finish1 - start1), (finish2 - start2))</SAMP> applications of the comparison function.</P> |
| <A NAME="sec6"><H3>Example</H3></A> |
| |
| <UL><PRE>// |
| // lex_comp.cpp |
| // |
| |
| #include <algorithm> |
| #include <functional> |
| #include <iostream> |
| #include <vector> |
| |
| int main() |
| { |
| typedef std::vector<int, std::allocator<int> > Vector; |
| |
| const Vector::value_type d1[] = { 1, 3, 5, 32, 64 }; |
| const Vector::value_type d2[] = { 1, 3, 2, 43, 56 }; |
| |
| // Create vectors. |
| Vector v1 (d1 + 0, d1 + sizeof d1 / sizeof *d1); |
| Vector v2 (d2 + 0, d2 + sizeof d1 / sizeof *d2); |
| |
| // Is v1 less than v2 (I think not). |
| bool b1 = std::lexicographical_compare (v1.begin (), |
| v1.end (), v2.begin (), v2.end ()); |
| |
| // Is v2 less than v1 (yup, sure is). |
| bool b2 = std::lexicographical_compare(v2.begin (), |
| v2.end (), v1.begin (), v1.end (), |
| std::less<int>()); |
| |
| std::cout << std::boolalpha << b1 |
| << " " << b2 << std::endl; |
| |
| return 0; |
| } |
| |
| |
| Program Output: |
| </PRE></UL> |
| <UL><PRE>false true |
| |
| </PRE></UL> |
| <A NAME="sec7"><H3>Standards Conformance</H3></A> |
| <P><I>ISO/IEC 14882:1998 -- International Standard for Information Systems -- Programming Language C++, Section 25.3.8</I></P> |
| |
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