std:: generate_n

If Size is not convertible to an integral type , the program is ill-formed.

Parameters

Return value

Iterator one past the last element assigned if count > 0 , first otherwise.

Complexity

Exactly std:: max ( 0 , count ) invocations of g ( ) and assignments.

Exceptions

The overload with a template parameter named ExecutionPolicy reports errors as follows:

• If execution of a function invoked as part of the algorithm throws an exception and ExecutionPolicy is one of the standard policies , std::terminate is called. For any other ExecutionPolicy , the behavior is implementation-defined.
• If the algorithm fails to allocate memory, std::bad_alloc is thrown.

Possible implementation

template<class OutputIt, class Size, class Generator>
constexpr // since C++20
OutputIt generate_n(OutputIt first, Size count, Generator g)
{
    for (Size i = 0; i < count; ++i, ++first)
        *first = g();
 
    return first;
}

Example

#include <algorithm>
#include <functional>
#include <iostream>
#include <iterator>
#include <random>
 
int main()
{
    std::mt19937 rng; // default constructed, seeded with fixed seed
    std::generate_n(std::ostream_iterator<std::mt19937::result_type>(std::cout, " "),
                    5, std::ref(rng));
    std::cout << '\n';
}

3499211612 581869302 3890346734 3586334585 545404204

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

See also