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<H2>generate, generate_n</H2>
<HR><PRE> Algorithm</PRE><HR>
<A NAME="Summary"><H3>Summary</H3></A>
<P>Initialize a container with values produced by a value-generator class.</P>
<H3>Contents</H3>
<UL>
<A HREF="#Synopsis"><LI>Synopsis</LI></A>
<A HREF="#Description"><LI>Description</LI></A>
<A HREF="#Complexity"><LI>Complexity</LI></A>
<A HREF="#Example"><LI>Example</LI></A>
<A HREF="#Warnings"><LI>Warnings</LI></A>
<A HREF="#See Also"><LI>See Also</LI></A>
</UL>
<A NAME="Synopsis"><H3>Synopsis</H3></A>
<PRE>#include <algorithm></PRE>
<PRE>
template <class ForwardIterator, class Generator>
void <B>generate</B>(ForwardIterator first, ForwardIterator last,
Generator gen);
template <class OutputIterator, class Size, class Generator>
void <B>generate_n</B>(OutputIterator first, Size n, Generator gen);
</PRE>
<A NAME="Description"><H3>Description</H3></A>
<P>A value-generator function returns a value each time it is invoked. The algorithms <B><I>generate</B></I> and <B><I>generate_n</B></I> initialize (or reinitialize) a sequence by assigning the return value of the generator function <SAMP>gen</SAMP> to all the elements designated by iterators in the range <SAMP>[first, last)</SAMP> or <SAMP>[first, first + n)</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><B><I>generate_n</B></I> assumes that there are at least <SAMP>n</SAMP> elements following <SAMP>first</SAMP>, unless <SAMP>first</SAMP> is an insert iterator.</P>
<A NAME="Complexity"><H3>Complexity</H3></A>
<P>The <B><I>generate</B></I> and <B><I>generate_n</B></I> algorithms invoke <SAMP>gen </SAMP>and assign its return value exactly<SAMP> last - first </SAMP>(or <SAMP>n</SAMP>) times.</P>
<A NAME="Example"><H3>Example</H3></A>
<PRE>//
// generate.cpp
//
#include <algorithm>
#include <vector>
#include <iostream.h>
// Value generator simply doubles the current value
// and returns it
template <class T>
class generate_val
{
private:
T val_;
public:
generate_val(const T& val) : val_(val) {}
T& operator()() { val_ += val_; return val_; }
};
int main()
{
int d1[4] = {1,2,3,4};
generate_val<int> gen(1);
// Set up two vectors
vector<int> v1(d1,d1 + 4), v2(d1,d1 + 4);
// Set up one empty vector
vector<int> v3;
// Generate values for all of v1
<B>generate</B>(v1.begin(),v1.end(),gen);
// Generate values for first 3 of v2
<B>generate_n</B>(v2.begin(),3,gen);
// Use insert iterator to generate 5 values for v3
<B>generate_n</B>(back_inserter(v3),5,gen);
// Copy all three to cout
ostream_iterator<int> out(cout," ");
copy(v1.begin(),v1.end(),out);
cout << endl;
copy(v2.begin(),v2.end(),out);
cout << endl;
copy(v3.begin(),v3.end(),out);
cout << endl;
// Generate 3 values for cout
<B>generate_n</B>(ostream_iterator<int>(cout," "),3,gen);
cout << endl;
return 0;
}
Output :
2 4 8 16
2 4 8 4
2 4 8 16 32
2 4 8
</PRE>
<A NAME="Warnings"><H3>Warnings</H3></A>
<P>If your compiler does not support default template parameters, then you need to always supply the <SAMP>Allocator</SAMP> template argument. For instance, you'll have to write:</P>
<PRE>vector<int, allocator></PRE>
<PRE></PRE><P>instead of :</P>
<PRE>vector<int></PRE>
<A NAME="See Also"><H3>See Also</H3></A>
<P><A HREF="Fun_7437.htm"><B><I>Function Objects</B></I></A></P>
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