< cpp‎ | algorithm
Algorithm library
Constrained algorithms and algorithms on ranges (C++20)
Concepts and utilities: std::Sortable, std::projected, ...
Constrained algorithms: std::ranges::copy, std::ranges::sort, ...
Execution policies (C++17)
Non-modifying sequence operations
Modifying sequence operations
Operations on uninitialized storage
Partitioning operations
Sorting operations
Binary search operations
Set operations (on sorted ranges)
Heap operations
Minimum/maximum operations
Numeric operations
C library
Defined in header <algorithm>
template< class ForwardIt, class Generator >
void generate( ForwardIt first, ForwardIt last, Generator g );
(until C++20)
template< class ForwardIt, class Generator >
constexpr void 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.


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 LegacyForwardIterator.

Return value



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


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 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();


#include <algorithm>
#include <iostream>
#include <vector>
int f()
    static int i = 1;
    return i++;
int main()
    std::vector<int> v(5);
    std::generate(v.begin(), v.end(), f);
    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";


v: 1 2 3 4 5
v: 0 1 2 3 4

See also

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