< cpp‎ | algorithm
Algorithm library
Constrained algorithms and algorithms on ranges (C++20)
Constrained algorithms, e.g. ranges::copy, ranges::sort, ...
Execution policies (C++17)
Non-modifying sequence operations
Batch operations
Search operations
(C++11)                (C++11)(C++11)

Modifying sequence operations
Copy operations
Swap operations
Transformation operations
Generation operations
Removing operations
Order-changing operations
(until C++17)(C++11)
Sampling operations

Sorting and related operations
Partitioning operations
Sorting operations
Binary search operations
(on partitioned ranges)
Set operations (on sorted ranges)
Merge operations (on sorted ranges)
Heap operations
Minimum/maximum operations
Lexicographical comparison operations
Permutation operations
C library
Numeric operations
Operations on uninitialized memory
Defined in header <algorithm>
template< class ForwardIt, class Generator >
void generate( ForwardIt first, ForwardIt last, Generator g );
(1) (constexpr 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 [firstlast) a value generated by the given function object g.
2) Same as (1), but executed according to policy.
This overload participates in overload resolution only if

std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true.

(until C++20)

std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>> is true.

(since C++20)


[edit] 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 LegacyForwardIterator.

[edit] Complexity

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

[edit] 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 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.

[edit] Possible implementation

template<class ForwardIt, class Generator>
constexpr //< since C++20
void generate(ForwardIt first, ForwardIt last, Generator g)
    for (; first != last; ++first)
        *first = g();

[edit] Example

#include <algorithm>
#include <iostream>
#include <vector>
void println(std::string_view fmt, const auto& v)
    for (std::cout << fmt; const auto& e : v)
        std::cout << e << ' ';
    std::cout << '\n';
int f()
    static int i;
    return ++i;
int main()
    std::vector<int> v(5);
    std::generate(v.begin(), v.end(), f);
    println("v: ", v);
    // 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++; });
    println("v: ", v);


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

[edit] See also

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