std::generate_n

 

C++

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Algorithms library

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Numerics library

Input/output library

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Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Technical Specifications

 

Algorithm library

Functions
Non-modifying sequence operations
all_ofany_ofnone_of (C++11)(C++11)(C++11) for_each countcount_if mismatch equal	findfind_iffind_if_not (C++11) find_end find_first_of adjacent_find search search_n
Modifying sequence operations
copycopy_if (C++11) copy_n (C++11) copy_backward move (C++11) move_backward (C++11) fill fill_n transform generate generate_n removeremove_if remove_copyremove_copy_if	replacereplace_if replace_copyreplace_copy_if swap swap_ranges iter_swap reverse reverse_copy rotate rotate_copy random_shuffleshuffle (until C++17)(C++11) unique unique_copy
Partitioning operations
is_partitioned (C++11) partition partition_copy (C++11)	stable_partition partition_point (C++11)
Sorting operations (on sorted ranges)
is_sorted (C++11) is_sorted_until (C++11) sort	partial_sort partial_sort_copy stable_sort nth_element
Binary search operations (on sorted ranges)
lower_bound upper_bound	binary_search equal_range
Set operations (on sorted ranges)
merge inplace_merge includes	set_difference set_intersection set_symmetric_difference set_union
Heap operations
is_heap (C++11) is_heap_until (C++11) make_heap	push_heap pop_heap sort_heap
Minimum/maximum operations
max max_element min min_element minmax (C++11) minmax_element (C++11)	lexicographical_compare is_permutation (C++11) next_permutation prev_permutation
Numeric operations
iota (C++11) accumulate inner_product	adjacent_difference partial_sum
C library
qsort	bsearch

 

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
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.

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.

Run this code

#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:

ar: 52894 15984720 41513563 41346135 51451456

See also

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)