std::ranges::fill_n

Since C++26

Header: <algorithm>

Assigns the given value to all elements in the range [first,first + n).

# Declarations

Call signature

template< class T, std::output_iterator<const T&> O >
constexpr O fill_n( O first, std::iter_difference_t<O> n, const T& value );

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

template< class O, class T = std::iter_value_t<O> >
requires std::output_iterator<O, const T&>
constexpr O fill_n( O first, std::iter_difference_t<O> n, const T& value );

(since C++26)

# Parameters

# Return value

An output iterator that compares equal to first + n.

# Notes

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

# Example

#include <algorithm>
#include <complex>
#include <iostream>
#include <string>
#include <vector>
 
void println(const auto& v)
{
    for (const auto& elem : v)
        std::cout << ' ' << elem;
    std::cout << '\n';
}
 
int main()
{
    constexpr auto n{8};
 
    std::vector<std::string> v(n, "▓▓░░");
    println(v);
 
    std::ranges::fill_n(v.begin(), n, "░░▓▓");
    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_n(nums.begin(), 2, {4, 2});
    #else
        std::ranges::fill_n(nums.begin(), 2, std::complex<double>{4, 2});
    #endif
    println(nums);
}

# See also