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std::generate_n

From cppreference.com
< cpp‎ | algorithm
 
 
 

Defined in header <algorithm>
template< class OutputIt, class Size, class Generator >
void generate_n( OutputIt first, Size count, Generator g );
(until C++11)
template< class OutputIt, class Size, class Generator >
OutputIt generate_n( OutputIt first, Size count, Generator g );
(since C++11)

Assigns values, generated by given function object g, to the first count elements in the range beginning at first, if count>0. Does nothing otherwise.

Contents

[edit] Parameters

first - the beginning of the range of elements to generate
count - number of the elements to generate
g - generator function object that will be called.

The signature of the function should be equivalent to the following:

Ret fun();

The type Ret must be such that an object of type OutputIt can be dereferenced and assigned a value of type Ret. ​

Type requirements
-
OutputIt must meet the requirements of OutputIterator.

[edit] Return value

(none) (until C++11)
Iterator one past the last element assigned if count>0, first otherwise. (since C++11)

[edit] Complexity

Exactly count invocations of g() and assignments, for count>0.

[edit] Possible implementation

template< class OutputIt, class Size, class Generator >
OutputIt generate_n( OutputIt first, Size count, Generator g )
{
    for( Size i = 0; i < count; i++ ) {
        *first++ = g();
    }
    return first;
}

[edit] Example

The following code fills an array of integers with random numbers.

#include <cstddef>
#include <cstdlib>
#include <iostream>
#include <iterator>
#include <algorithm>
 
int main()
{
    const std::size_t N = 5;
    int ar[N];
    std::generate_n(ar, N, std::rand); // Using the C function rand()
 
    std::cout << "ar: ";
    std::copy(ar, ar+N, std::ostream_iterator<int>(std::cout, " "));
    std::cout << "\n";
}

Possible output:

ar: 52894 15984720 41513563 41346135 51451456

[edit] See also

assigns a value to a number of elements
(function template) [edit]
saves the result of a function in a range
(function template) [edit]