std::generate_n

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Algorithm library

Constrained algorithms and algorithms on ranges(C++20)

Constrained algorithms, e.g.ranges::copy,ranges::sort, ...

Execution policies(C++17)

is_execution_policy

(C++17)

execution::seqexecution::parexecution::par_unseqexecution::unseq

(C++17) (C++17)(C++17)(C++20)

execution::sequenced_policyexecution::parallel_policyexecution::parallel_unsequenced_policyexecution::parallel_unsequenced

(C++17)(C++17)(C++17)(C++20)

Non-modifying sequence operations

(C++17)

all_ofany_ofnone_of (C++11) (C++11)(C++11)
countcount_if
mismatch
equal

findfind_iffind_if_not (C++11)
find_end
find_first_of
adjacent_find
search
search_n

Modifying sequence operations

Copy operations

copycopy_if (C++11)
copy_backward

copy_n (C++11)
move (C++11)
move_backward (C++11)

Swap operations

swap
iter_swap

swap_ranges

Transformation operations

replacereplace_if
transform

replace_copyreplace_copy_if

Generation operations

fill
fill_n

generate
generate_n

Removing operations

removeremove_if
unique

remove_copyremove_copy_if
unique_copy

Order-changing operations

reverse
reverse_copy
rotate
rotate_copy

random_shuffleshuffle (until C++17)(C++11)
shift_leftshift_right (C++20)(C++20)

Sampling operations

sample

(C++17)

Sorting and related operations

Partitioning operations

partition
partition_copy (C++11)
stable_partition

is_partitioned (C++11)
partition_point (C++11)

Sorting operations

sort
stable_sort
partial_sort
partial_sort_copy

is_sorted (C++11)
is_sorted_until (C++11)
nth_element

Binary search operations
(on partitioned ranges)

lower_bound
upper_bound

equal_range
binary_search

Set operations (on sorted ranges)

includes
set_union
set_intersection

set_difference
set_symmetric_difference

Merge operations (on sorted ranges)

merge

inplace_merge

Heap operations

push_heap
pop_heap
make_heap

sort_heap
is_heap (C++11)
is_heap_until (C++11)

Minimum/maximum operations

max
min
minmax (C++11)
clamp (C++17)

max_element
min_element
minmax_element (C++11)

Lexicographical comparison operations

lexicographical_compare

lexicographical_compare_three_way

(C++20)

Permutation operations

next_permutation
prev_permutation

is_permutation (C++11)

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)

Operations on uninitialized memory

uninitialized_copy
uninitialized_move (C++17)
uninitialized_fill

uninitialized_copy_n (C++11)
uninitialized_move_n (C++17)
uninitialized_fill_n

destroy (C++17)
destroy_n (C++17)
destroy_at (C++17)
construct_at (C++20)

uninitialized_default_construct (C++17)
uninitialized_value_construct (C++17)
uninitialized_default_construct_n (C++17)
uninitialized_value_construct_n (C++17)

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Defined in header`<algorithm>`
template<class OutputIt,class Size,class Generator> OutputIt generate_n( OutputIt first, Size count, Generator g);	(1)	(constexpr 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 objectg, to the firstcount elements in the range beginning atfirst, ifcount>0. Does nothing otherwise.

2) Same as(1), but executed according topolicy.

This overload participates in overload resolution only if all following conditions are satisfied:

std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> istrue.	(until C++20)
std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>> istrue.	(since C++20)

IfSize is notconvertible to anintegral type, the program is ill-formed.

[edit]Parameters

first - the beginning of the range of elements to generate

count - number of the elements to generate

policy - theexecution policy to use

generator function object that will be called.

The signature of the function should be equivalent to the following:

Ret fun();

The typeRet must be such that an object of typeOutputIt can be dereferenced and assigned a value of typeRet.

Type requirements

OutputIt must meet the requirements ofLegacyOutputIterator.

ForwardIt must meet the requirements ofLegacyForwardIterator.

[edit]Return value

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

[edit]Complexity

Exactlystd::max(0, count) invocations ofg() and assignments.

[edit]Exceptions

The overload with a template parameter namedExecutionPolicy reports errors as follows:

If execution of a function invoked as part of the algorithm throws an exception andExecutionPolicy is one of thestandard 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.

[edit]Possible implementation

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

[edit]Example

Run this code

#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';}

Output:

3499211612 581869302 3890346734 3586334585 545404204

[edit]Defect reports

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

DR	Applied to	Behavior as published	Correct behavior
LWG 426	C++98	the complexity requirement was “exactlycount invocations or assignments”, which is broken ifcount is negative	no invocation or assignment ifcount is non-positive
LWG 865	C++98	the location of the first element following the generation range was not returned	returned

[edit]See also

fill_n	copy-assigns the given value to N elements in a range (function template)[edit]
generate	assigns the results of successive function calls to every element in a range (function template)[edit]
ranges::generate_n (C++20)	saves the result of N applications of a function (algorithm function object)[edit]