166 lines
6.5 KiB
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166 lines
6.5 KiB
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<HTML>
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<HEAD>
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<TITLE>generate(), generate_n()</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="functional-h.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="get-temporary-buffer.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>generate(), generate_n()</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">See Also</A></LI>
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<LI><A HREF="#sec8">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 assigns each element in a range a value produced by repeated application of the given function object</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 ForwardIterator, class Generator>
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void generate(ForwardIterator start, ForwardIterator finish,
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Generator gen);
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template <class OutputIterator, class Size, class Generator>
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void generate_n(OutputIterator start, Size n,
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Generator gen);
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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>A value-generator function returns a value each time it is invoked. The algorithms <SAMP>generate()</SAMP> and <SAMP><A HREF="generate.html">generate_n()</A></SAMP> assign each element in the sequence <SAMP>[start, finish)</SAMP> or <SAMP>[start, start + n) </SAMP>the return value of the generator function <SAMP>gen()</SAMP>. The function <SAMP>gen()</SAMP> takes no arguments. (<SAMP>gen()</SAMP> can be a function or a class with an <SAMP>operator()</SAMP> defined that takes no arguments.)</P>
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<P><SAMP><A HREF="generate.html">generate_n()</A></SAMP> assumes that all iterators in the range <SAMP>[start, start + n]</SAMP> are dereferenceable, unless <SAMP>start</SAMP> is an insert iterator.</P>
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<A NAME="sec5"><H3>Complexity</H3></A>
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<P>The <SAMP>generate()</SAMP> and <SAMP><A HREF="generate.html">generate_n()</A></SAMP> algorithms invoke <SAMP>gen()</SAMP> and assign its return value exactly <SAMP>finish - start</SAMP> (or <SAMP>n</SAMP>) times.</P>
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<A NAME="sec6"><H3>Example</H3></A>
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<UL><PRE>//
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// generate.cpp
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//
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#include <algorithm> // for generate, generate_n
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#include <iostream> // for cout, endl
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#include <vector> // for vector
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// Value generator simply doubles the current value
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// and returns it.
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template <class T>
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class generator
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{
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T val_;
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public:
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generator(const T &val) : val_ (val) { }
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T operator()() {
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return val_ += val_;
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}
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};
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int main ()
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{
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// Typedef for convenience.
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typedef std::vector<short,
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std::allocator<short> > vector;
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vector::value_type arr[4] = { 1, 2, 3, 4 };
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// Set up two vectors.
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vector v1(arr, arr + sizeof arr / sizeof *arr);
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vector v2 = v1;
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// Set up one empty vector.
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vector v3;
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// Create a generator function object.
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generator<vector::value_type> gen(1);
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// Generate values for all of v1.
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std::generate(v1.begin(), v1.end(), gen);
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// Generate values for first 3 of v2.
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std::generate_n(v2.begin(), 3, gen);
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// Use back_insert_iterator to generate 5 values for v3.
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std::generate_n(std::back_inserter(v3), 5, gen);
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// Copy all three to cout.
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std::ostream_iterator<vector::value_type, char,
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std::char_traits<char> > out(std::cout, " ");
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std::copy(v1.begin(), v1.end(), out);
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std::cout << std::endl;
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std::copy(v2.begin(), v2.end(), out);
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std::cout << std::endl;
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std::copy(v3.begin(), v3.end(), out);
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std::cout << std::endl;
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// Generate 3 values into cout.
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std::generate_n(out, 3, gen);
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std::cout << 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>2 4 8 16
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2 4 8 4
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2 4 8 16 32
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2 4 8
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</PRE></UL>
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<A NAME="sec7"><H3>See Also</H3></A>
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<P><A HREF="functionobjects.html">Function Objects</A></P>
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<A NAME="sec8"><H3>Standards Conformance</H3></A>
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<P><I>ISO/IEC 14882:1998 -- International Standard for Information Systems -- Programming Language C++, Section 25.2.6</I></P>
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<BR>
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