std::generate_n

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.

Parameters

first - the beginning of the range of elements to generate

count - number of the elements to generate

generator function object that will be called.

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

1	`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.

Return value

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

Complexity

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

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;
}

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:

1	`ar: 52894 15984720 41513563 41346135 51451456`

fill_n	assigns a value to a number of elements (function template)
generate	saves the result of a function in a range (function template)
std::experimental::parallel::generate_n (parallelism TS)	parallelized version of `std::generate_n` (function template)