# std::ranges::fill

From cppreference.com
< cpp‎ | algorithm‎ | ranges

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)

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.

Run this code

    #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

### See also

ranges::fill_n (C++20) | assigns a value to a number of elements (niebloid)
ranges::copy ranges::copy_if (C++20)(C++20) | copies a range of elements to a new location (niebloid)
ranges::generate (C++20) | saves the result of a function in a range (niebloid)
ranges::transform (C++20) | applies a function to a range of elements (niebloid)
fill | copy-assigns the given value to every element in a range (function template)

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