std::generate_n(3) | C++ Standard Libary | std::generate_n(3) |
NAME¶
std::generate_n - std::generate_n
Synopsis¶
Defined in header <algorithm>
template< class OutputIt, class Size, class Generator > (until
C++11)
void generate_n( OutputIt first, Size count, Generator g );
template< class OutputIt, class Size, class Generator > (since
C++11)
OutputIt generate_n( OutputIt first, Size count, Generator g (until
C++20)
);
template< class OutputIt, class Size, class Generator >
constexpr OutputIt generate_n( OutputIt first, Size count, (since
C++20)
Generator g ); (1)
template< class ExecutionPolicy, class ForwardIt , class Size,
class Generator >
ForwardIt generate_n( ExecutionPolicy&& policy, ForwardIt (2)
(since C++17)
first,
Size count, Generator g );
1) 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.
2) Same as (1), but executed according to policy. This overload does
not participate
in overload resolution unless
std::is_execution_policy_v<std::decay_t<ExecutionPolicy>>
(until C++20)
std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>>
(since C++20) is true.
Parameters¶
first - the beginning of the range of elements to generate
count - number of the elements to generate
policy - the execution policy to use. See execution policy for details.
generator function object that will be called.
The signature of the function should be equivalent to the following:
g -
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 LegacyOutputIterator.
-
ForwardIt must meet the requirements of LegacyForwardIterator.
Return value¶
(none) (until C++11)
Iterator one past the last element assigned if count>0, first (since
C++11)
otherwise.
Complexity¶
Exactly count invocations of g() and assignments, for count>0.
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 // void until C++11
generate_n( OutputIt first, Size count, Generator g )
{
for( Size i = 0; i < count; ++i ) {
*first++ = g();
}
return first;
}
Example¶
// Run this code
#include <random>
#include <iostream>
#include <iterator>
#include <algorithm>
#include <functional>
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';
}
Output:¶
3499211612 581869302 3890346734 3586334585 545404204
See also¶
fill_n copy-assigns the given value to N elements in a range
(function template)
assigns the results of successive function calls to every element
generate in a range
(function template)
ranges::generate_n saves the result of N applications of a function
(C++20) (niebloid)
2022.07.31 | http://cppreference.com |