Std::iota (3) Linux Manual Page

std::iota – std::iota

Synopsis

Defined in header<numeric>

    template <class ForwardIt, class T>
    (since C++ 11)

        void iota(ForwardIt first, ForwardIt last, T value);

Fills the range [first, last) with sequentially increasing values, starting with value and repetitively evaluating ++value.
Equivalent operation:

*(d_first)   = value;

*(d_first+1) = ++value;

*(d_first+2) = ++value;

*(d_first+3) = ++value;

...

Parameters

first, last – the range of elements to fill with sequentially increasing values starting with value
value – initial value to store, the expression ++value must be well-formed

Return value

(none)

Complexity

Exactly last – first increments and assignments.

Possible implementation

  template<class ForwardIt, class T>
  void iota(ForwardIt first, ForwardIt last, T value)
  {
      while(first != last) {
          *first++ = value;
          ++value;
      }
  }

Notes

The function is named after the integer function ⍳ from the programming language APL. It was one of the STL_components that were not included in C++98, but eventually made it into the standard library in C++11.

Example

The following example applies std::shuffle to a vector of std::list iterators since std::shuffle cannot be applied to a std::list directly. std::iota is used to populate both containers.
// Run this code

#include <algorithm>

#include <iostream>

#include <list>

#include <numeric>

#include <random>

#include <vector>
int main()

{
    std::list<int> l(10);
    std::iota(l.begin(), l.end(), -4);
    std::vector<std::list<int>::iterator> v(l.size());
    std::iota(v.begin(), v.end(), l.begin());
    std::shuffle(v.begin(), v.end(), std::mt19937{std::random_device{}()});
    std::cout << "Contents of the list: ";
    for (auto n : l)
        std::cout << n << ' ';
    std::cout << '\n';
    std::cout << "Contents of the list, shuffled: ";
    for (auto i : v)
        std::cout << *i << ' ';
    std::cout << '\n';
}

Possible output:

Contents of the list: -4 -3 -2 -1 0 1 2 3 4 5
Contents of the list, shuffled: 0 -1 3 4 -4 1 -2 -3 2 5

std::iota (3) Linux Manual Page