std::iota

Header: <numeric>

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

# Declarations

template< class ForwardIt, class T >
void iota( ForwardIt first, ForwardIt last, T value );

(since C++11) (constexpr since C++20)

# Parameters

# 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 made it into the standard library in C++11.

# Example

#include <algorithm>
#include <iomanip>
#include <iostream>
#include <list>
#include <numeric>
#include <random>
#include <vector>
 
class BigData // inefficient to copy
{
    int data[1024]; /* some raw data */
public:
    explicit BigData(int i = 0) { data[0] = i; /* ... */ }
    operator int() const { return data[0]; }
    BigData& operator=(int i) { data[0] = i; return *this; }
    /* ... */
};
 
int main()
{
    std::list<BigData> l(10);
    std::iota(l.begin(), l.end(), -4);
 
    std::vector<std::list<BigData>::iterator> v(l.size());
    std::iota(v.begin(), v.end(), l.begin());
    // Vector of iterators (to original data) is used to avoid expensive copying,
    // and because std::shuffle (below) cannot be applied to a std::list directly.
 
    std::shuffle(v.begin(), v.end(), std::mt19937{std::random_device{}()});
 
    std::cout << "Original contents of the list l:\t";
    for (const auto& n : l)
        std::cout << std::setw(2) << n << ' ';
    std::cout << '\n';
 
    std::cout << "Contents of l, viewed via shuffled v:\t";
    for (const auto i : v)
        std::cout << std::setw(2) << *i << ' ';
    std::cout << '\n';
}

# See also