std::generate

 

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Technical Specifications

 

Algorithm library

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)
Modifying sequence operations
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)
Operations on uninitialized storage
uninitialized_copy uninitialized_move (C++17)	uninitialized_copy_n (C++11) uninitialized_move_n (C++17)	uninitialized_fill	uninitialized_fill_n
Partitioning operations
is_partitioned (C++11) partition_point (C++11)	partition partition_copy (C++11)	stable_partition
Sorting operations
is_sorted (C++11) is_sorted_until (C++11)	sort stable_sort	partial_sort partial_sort_copy	nth_element
Binary search operations
lower_bound	upper_bound	binary_search	equal_range
Set operations (on sorted ranges)
merge inplace_merge	set_difference set_intersection	set_symmetric_difference set_union	includes
Heap operations
is_heap (C++11) is_heap_until (C++11)	make_heap sort_heap	push_heap pop_heap
Minimum/maximum operations
max max_element	min min_element	minmax (C++11) minmax_element (C++11)	clamp (C++17) compare_3way (C++20)
Permutations
is_permutation (C++11)	next_permutation	prev_permutation
Numeric operations
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 ForwardIt, class Generator > void generate( ForwardIt first, ForwardIt last, Generator g );			(until C++20)
template<class ForwardIt, class Generator > constexprvoid generate( ForwardIt first, ForwardIt last, Generator g );			(since C++20)
template<class ExecutionPolicy, class ForwardIt, class Generator > void generate( ExecutionPolicy&& policy, ForwardIt first, ForwardIt last, Generator g );		(2)	(since C++17)

1) Assigns each element in range [first, last) a value generated by the given function object g.

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, last	-	the range of 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 ForwardIt can be dereferenced and assigned a value of type Ret. ​
Type requirements
- ForwardIt must meet the requirements of ForwardIterator.

Return value

(none)

Complexity

Exactly std::distance(first, last) invocations of g() and assignments.

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 ForwardIt, class Generator>void generate(ForwardIt first, ForwardIt last, Generator g){while(first != last){*first++= g();}}

Example

The following code fills a vector with random numbers:

Run this code

#include <algorithm>#include <iostream>#include <vector>#include <cstdlib>   int main(){std::vector<int> v(5);std::srand(0);//Just for example std::generate(v.begin(), v.end(), std::rand);// Using the C function std::rand()   std::cout<<"v: ";for(auto iv: v){std::cout<< iv <<" ";}std::cout<<"\n";   // Initialize with default values 0,1,2,3,4 from a lambda function// Equivalent to std::iota(v.begin(), v.end(), 0); std::generate(v.begin(), v.end(), [n =0]() mutable {return n++;});   std::cout<<"v: ";for(auto iv: v){std::cout<< iv <<" ";}std::cout<<"\n";}

Possible output:

v: 1804289383 846930886 1681692777 1714636915 1957747793 v: 0 1 2 3 4

See also

fill	copy-assigns the given value to every element in a range (function template)
generate_n	assigns the results of successive function calls to N elements in a range (function template)
iota (C++11)	fills a range with successive increments of the starting value (function template)