std::generate (3) - Linux Manuals

std::generate: std::generate

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 > (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