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std::ranges::fill

Defined in header <algorithm>

Call signature

Defined in header `<algorithm>`
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 );	(1)	(since C++20)
template< class T, ranges::output_range<const T&> R > constexpr ranges::borrowed_iterator_t<R> fill( R&& r, const T& value );	(2)	(since C++20)

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

(1)

(since C++20)

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

(2)

(since C++20)

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

2) Same as (1), but uses r as the source range, as if using ranges::begin(r) as first and ranges::end(r) as last.

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

first, last	-	the range of elements to modify
r	-	the range of elements to modify
value	-	the value to be assigned

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

The following code uses ranges::fill to set all elements of std::vector<int> first to -1, then to 10.

#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);
}

Output:

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