< cpp‎ | algorithm
Algorithm library
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 );
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 does not participate in overload resolution unless 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 ForwardIterator.

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 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();


The following code fills a vector with random numbers:

#include <algorithm>
#include <iostream>
#include <vector>
#include <cstdlib>
int main()
    std::vector<int> v(5);
    std::generate(v.begin(), v.end(), std::rand); // Using the C function 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);
    int n = {0};
    std::generate(v.begin(), v.end(), [&n]{ return n++; });
    std::cout << "v: ";
    for (auto iv: v) {
        std::cout << iv << " ";
    std::cout << "\n";

Possible output:

v: 52894 15984720 41513563 41346135 51451456
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)