std::iota (3) - Linux Manuals

std::iota: std::iota

NAME

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