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| <TITLE>for_each()</TITLE> |
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| <H2>for_each()</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">See Also</A></LI> |
| <LI><A HREF="#sec8">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 applies a function to each element in a range</P> |
| <A NAME="sec3"><H3>Synopsis</H3></A> |
| |
| <PRE>#include <algorithm> |
| |
| namespace std { |
| template <class InputIterator, class Function> |
| void Function for_each(InputIterator start, |
| InputIterator finish, |
| Function f); |
| } |
| </PRE> |
| <A NAME="sec4"><H3>Description</H3></A> |
| <P>The <SAMP>for_each()</SAMP> algorithm applies the function object <SAMP>f</SAMP> to each value in the range <SAMP>[start, finish)</SAMP>, where <SAMP>start</SAMP> and <SAMP>finish</SAMP> are iterators that define the sequence. Since this a non-mutating algorithm, the function <SAMP>f</SAMP> cannot make any modifications to the sequence, but it can achieve results through side effects (such as copying or printing). If <SAMP>f</SAMP> returns a result, the result is ignored.</P> |
| <P><SAMP>for_each()</SAMP> returns the function object <SAMP>f</SAMP>.</P> |
| <A NAME="sec5"><H3>Complexity</H3></A> |
| <P>The function object <SAMP>f</SAMP> is applied exactly <SAMP>finish - start</SAMP> times.</P> |
| <A NAME="sec6"><H3>Example</H3></A> |
| |
| <UL><PRE>// |
| // for_each.cpp |
| // |
| |
| #include <algorithm> // for for_each |
| #include <functional> // for less, unary_function |
| #include <iostream> // for cout, endl |
| #include <set> // for set |
| |
| |
| |
| // Function object that outputs its argument times x. |
| template <class Arg> |
| class out_times_x: public std::unary_function<Arg, void> |
| { |
| Arg multiplier; |
| public: |
| out_times_x(const Arg &x) : multiplier (x) { } |
| |
| void operator()(const Arg &x) const { |
| std::cout << x * multiplier << " " << std::endl; |
| } |
| }; |
| |
| |
| int main () |
| { |
| // Typedef for convenience. |
| typedef std::set<int, std::less<int>, |
| std::allocator<int> > sequence; |
| |
| sequence::value_type arr [] = { 1, 2, 3, 4, 5 }; |
| |
| // Populate a sequence from arr. |
| sequence s(arr, arr + sizeof arr / sizeof *arr); |
| |
| // Construct a function object. |
| out_times_x<sequence::value_type> f2(2); |
| |
| // Apply function object's operator() to each element. |
| std::for_each(s.begin(), s.end(), f2); |
| |
| return 0; |
| } |
| |
| |
| Program Output |
| </PRE></UL> |
| <UL><PRE>2 |
| 4 |
| 6 |
| 8 |
| 10 |
| </PRE></UL> |
| <A NAME="sec7"><H3>See Also</H3></A> |
| <P><A HREF="algorithms.html">Algorithms</A>, <A HREF="functionobjects.html">Function Objects</A></P> |
| <A NAME="sec8"><H3>Standards Conformance</H3></A> |
| <P><I>ISO/IEC 14882:1998 -- International Standard for Information Systems -- Programming Language C++, Section 25.1.1</I></P> |
| |
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