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| <TITLE>generate(), generate_n()</TITLE> |
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| <H2>generate(), generate_n()</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 assigns each element in a range a value produced by repeated application of the given function object</P> |
| <A NAME="sec3"><H3>Synopsis</H3></A> |
| |
| <PRE>#include <algorithm> |
| |
| namespace std { |
| template <class ForwardIterator, class Generator> |
| void generate(ForwardIterator start, ForwardIterator finish, |
| Generator gen); |
| |
| template <class OutputIterator, class Size, class Generator> |
| void generate_n(OutputIterator start, Size n, |
| Generator gen); |
| } |
| </PRE> |
| <A NAME="sec4"><H3>Description</H3></A> |
| <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> |
| <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> |
| <A NAME="sec5"><H3>Complexity</H3></A> |
| <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> |
| <A NAME="sec6"><H3>Example</H3></A> |
| |
| <UL><PRE>// |
| // generate.cpp |
| // |
| |
| #include <algorithm> // for generate, generate_n |
| #include <iostream> // for cout, endl |
| #include <vector> // for vector |
| |
| |
| |
| // Value generator simply doubles the current value |
| // and returns it. |
| template <class T> |
| class generator |
| { |
| T val_; |
| public: |
| generator(const T &val) : val_ (val) { } |
| T operator()() { |
| return val_ += val_; |
| } |
| }; |
| |
| |
| int main () |
| { |
| // Typedef for convenience. |
| typedef std::vector<short, |
| std::allocator<short> > vector; |
| |
| vector::value_type arr[4] = { 1, 2, 3, 4 }; |
| |
| // Set up two vectors. |
| vector v1(arr, arr + sizeof arr / sizeof *arr); |
| vector v2 = v1; |
| |
| // Set up one empty vector. |
| vector v3; |
| |
| // Create a generator function object. |
| generator<vector::value_type> gen(1); |
| |
| // Generate values for all of v1. |
| std::generate(v1.begin(), v1.end(), gen); |
| |
| // Generate values for first 3 of v2. |
| std::generate_n(v2.begin(), 3, gen); |
| |
| // Use back_insert_iterator to generate 5 values for v3. |
| std::generate_n(std::back_inserter(v3), 5, gen); |
| |
| // Copy all three to cout. |
| std::ostream_iterator<vector::value_type, char, |
| std::char_traits<char> > out(std::cout, " "); |
| |
| std::copy(v1.begin(), v1.end(), out); |
| std::cout << std::endl; |
| |
| std::copy(v2.begin(), v2.end(), out); |
| std::cout << std::endl; |
| |
| std::copy(v3.begin(), v3.end(), out); |
| std::cout << std::endl; |
| |
| // Generate 3 values into cout. |
| std::generate_n(out, 3, gen); |
| std::cout << std::endl; |
| |
| return 0; |
| } |
| |
| |
| Program Output: |
| </PRE></UL> |
| <UL><PRE>2 4 8 16 |
| 2 4 8 4 |
| 2 4 8 16 32 |
| 2 4 8 |
| </PRE></UL> |
| <A NAME="sec7"><H3>See Also</H3></A> |
| <P><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 25.2.6</I></P> |
| |
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