Std::generate (3) Linux Manual Page

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>
(1)(since C++ 20)

    constexpr void generate(ForwardIt first, ForwardIt last, Generator g);

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 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.
              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>
  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 = 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";
}

Output:

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

std::generate (3) Linux Manual Page