std::ranges::fill

Since C++26

Header: <algorithm>

  1. Assigns the given value to the elements in the range [first,last).

# Declarations

Call signature

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

(since C++20) (until C++26)

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

(since C++26)

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

(since C++20) (until C++26)

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

(since C++26)

# Parameters

# Return value

An output iterator that compares equal to last.

# Notes

Feature-test macro Value Std Feature __cpp_lib_algorithm_default_value_type 202403 (C++26) List-initialization for algorithms (1,2)

# Example

#include <algorithm>
#include <complex>
#include <iostream>
#include <vector>
 
void println(const auto& seq)
{
    for (const auto& e : seq)
        std::cout << e << ' ';
    std::cout << '\n';
}
 
int main()
{
    std::vector<int> v{0, 1, 2, 3, 4, 5};
 
    // set all elements to -1 using overload (1)
    std::ranges::fill(v.begin(), v.end(), -1);
    println(v);
 
    // set all element to 10 using overload (2)
    std::ranges::fill(v, 10);
    println(v);
 
    std::vector<std::complex<double>> nums{{1, 3}, {2, 2}, {4, 8}};
    println(nums);
    #ifdef __cpp_lib_algorithm_default_value_type
        std::ranges::fill(nums, {4, 2}); // T gets deduced
    #else
        std::ranges::fill(nums, std::complex<double>{4, 2});
    #endif
    println(nums);
}

# See also