std::ranges::fill

template< class T, std::output_iterator<const T&> O, std::sentinel_for<O> S >
constexpr O
    fill( O first, S last, const T& value );

template< class T, ranges::output_range<const T&> R >
constexpr ranges::borrowed_iterator_t<R>
    fill( R&& r, const T& value );

The function-like entities described on this page are niebloids, that is:

• Explicit template argument lists cannot be specified when calling any of them.
• None of them are visible to argument-dependent lookup.
• When any of them are found by normal unqualified lookup as the name to the left of the function-call operator, argument-dependent lookup is inhibited.

In practice, they may be implemented as function objects, or with special compiler extensions.

Parameters

Return value

An output iterator that compares equal to last.

Complexity

Exactly last - first assignments.

Possible implementation

struct fill_fn
{
    template<class T, std::output_iterator<const T&> O, std::sentinel_for<O> S>
    constexpr O operator()(O first, S last, const T& value) const
    {
        while (first != last)
            *first++ = value;
 
        return first;
    }
 
    template<class T, ranges::output_range<const T&> R>
    constexpr ranges::borrowed_iterator_t<R> operator()(R&& r, const T& value) const
    {
        return (*this)(ranges::begin(r), ranges::end(r), value);
    }
};
 
inline constexpr fill_fn fill;

Example

#include <algorithm>
#include <iostream>
#include <vector>
 
void println(std::vector<int> const& vi)
{
    for (int e : vi)
        std::cout << e << ' ';
    std::cout << '\n';
}
 
int main()
{
    std::vector<int> v {0, 1, 2, 3, 4, 5, 6, 7, 8, 9};
 
    std::ranges::fill(v.begin(), v.end(), -1);
    println(v);
 
    std::ranges::fill(v, 10);
    println(v);
}

-1 -1 -1 -1 -1 -1 -1 -1 -1 -1
10 10 10 10 10 10 10 10 10 10

See also