std::generate_n

 

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Execution policies (C++17)
is_execution_policy	execution::seqexecution::parexecution::par_unseq	execution::sequenced_policyexecution::parallel_policyexecution::parallel_unsequenced_policy
Non-modifying sequence operations
all_ofany_ofnone_of (C++11)(C++11)(C++11) for_each for_each_n (C++17)	countcount_if mismatch equal adjacent_find	findfind_iffind_if_not (C++11) find_end find_first_of	search search_n lexicographical_compare lexicographical_compare_3way (C++20)
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copycopy_if (C++11) copy_n (C++11) copy_backward move (C++11) move_backward (C++11) transform	fill fill_n generate generate_n swap iter_swap swap_ranges sample (C++17)	removeremove_if replacereplace_if reverse rotate unique random_shuffle (until C++17)	remove_copyremove_copy_if replace_copyreplace_copy_if reverse_copy rotate_copy unique_copy shuffle (C++11)
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uninitialized_copy uninitialized_move (C++17)	uninitialized_copy_n (C++11) uninitialized_move_n (C++17)	uninitialized_fill	uninitialized_fill_n
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is_partitioned (C++11) partition_point (C++11)	partition partition_copy (C++11)	stable_partition
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is_permutation (C++11)	next_permutation	prev_permutation
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iota (C++11) inner_product adjacent_difference	accumulate reduce (C++17) transform_reduce (C++17)	partial_sum inclusive_scan (C++17) exclusive_scan (C++17)	transform_inclusive_scan (C++17) transform_exclusive_scan (C++17)
C library
qsort	bsearch

 

Defined in header <algorithm>
	(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)
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 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.
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.
- ForwardIt must meet the requirements of ForwardIterator.

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.

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 three 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 > 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.

Run this code

#include <cstddef>#include <cstdlib>#include <iostream>#include <iterator>#include <algorithm>   int main(){conststd::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

See also

fill_n	copy-assigns the given value to N elements in a range (function template)
generate	assigns the results of successive function calls to every element in a range (function template)