std::generate_n
From cppreference.com
Defined in header <algorithm>
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(1) | ||
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) (until C++20) |
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template< class OutputIt, class Size, class Generator > constexpr OutputIt generate_n( OutputIt first, Size count, Generator g ); |
(since C++20) | |
template< class ExecutionPolicy, class ForwardIt , class Size, class Generator > ForwardIt generate_n( ExecutionPolicy&& policy, ForwardIt first, Size count, Generator g ); |
(2) | (since C++17) |
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 only participates in overload resolution if std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is trueParameters
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. | ||||||
g | - | generator function object that will be called. The signature of the function should be equivalent to the following:
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.
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-ForwardIt must meet the requirements of LegacyForwardIterator.
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Return value
(none) |
(until C++11) |
Iterator one past the last element assigned if |
(since C++11) |
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 otherExecutionPolicy
, 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 > OutputIt 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
copy-assigns the given value to N elements in a range (function template) | |
assigns the results of successive function calls to every element in a range (function template) |