NAME¶

std::generate - std::generate

Synopsis¶

Defined in header <algorithm>
template< class ForwardIt, class Generator > (until C++20)
void generate( ForwardIt first, ForwardIt last, Generator g );
template< class ForwardIt, class Generator >
constexpr void generate( ForwardIt first, ForwardIt last, (since C++20)
Generator g ); (1)
template< class ExecutionPolicy, class ForwardIt, class
Generator > (2) (since C++17)
void generate( ExecutionPolicy&& policy, ForwardIt first,
ForwardIt last, Generator g );

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>>
(until C++20)
std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>>
(since C++20) is true.

Parameters¶

first, last - the range of elements to generate
policy - the execution policy to use. See execution policy for details.
generator function object that will be called.

The signature of the function should be equivalent to the following:
g -
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¶

(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 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>
constexpr // Since C++20
void generate(ForwardIt first, ForwardIt last, Generator g)
{
while (first != last) {
*first++ = g();
}
}

Example¶

// Run this code

#include <algorithm>
#include <iostream>
#include <vector>

int f()
{
static int i;
return ++i;
}

int main()
{
std::vector<int> v(5);
auto print = [&] {
for (std::cout << "v: "; auto iv: v)
std::cout << iv << " ";
std::cout << "\n";
};

std::generate(v.begin(), v.end(), f);
print();

// 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++; });
print();
}

Output:¶

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

See also¶

fill 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
generate_n range
(function template)
iota fills a range with successive increments of the starting value
(C++11) (function template)
ranges::generate saves the result of a function in a range
(C++20) (niebloid)