generate(3C++)

Standard C++ Library
Copyright 1998, Rogue Wave Software, Inc.

NAME

generate, generate_n

- Initialize a container with values produced by a value-generator class.

SYNOPSIS

#include <algorithm>

template <class ForwardIterator, class Generator>

void generate(ForwardIterator first, ForwardIterator last,

Generator gen);

template <class OutputIterator, class Size, class Generator>

void generate_n(OutputIterator first, Size n, Generator gen);

DESCRIPTION

A value-generator function returns a value each time it is invoked. The algorithms generate and generate_n initialize (or reinitialize) a sequence by assigning the return value of the generator function gen to all the elements designated by iterators in the range [first, last) or [first, first + n). The function gen takes no arguments. (gen can be a function or a class with an operator () defined that takes no arguments.)

generate_n assumes that there are at least n elements following first, unless first is an insert iterator.

COMPLEXITY

The generate and generate_n algorithms invoke gen and assign its return value exactly last - first (or n) times.

EXAMPLE

//
// generate.cpp
//

#include <algorithm>
#include <vector>
#include <iostream>

using namespace std;

// 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
generate(v1.begin(),v1.end(),gen);

// Generate values for first 3 of v2
generate_n(v2.begin(),3,gen);

// Use insert iterator to generate 5 values for v3
generate_n(back_inserter(v3),5,gen);

// Copy all three to cout

ostream_iterator<int,char> 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
generate_n(ostream_iterator<int>(cout," "),3,gen);

cout << endl;

return 0;

}

Program Output

2 4 8 16
2 4 8 4
2 4 8 16 32
2 4 8

WARNINGS

If your compiler does not support default template parameters, then you always need to supply the Allocator template argument. For instance, you have to write:

vector<int, allocator<int> >

instead of:

vector<int>

If your compiler does not support namespaces, then you do not need the using declaration for std.

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