std::ranges::fill

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 may not be specified when calling any of them.
None of them is visible to argument-dependent lookup.
When one of them is found by normal unqualified lookup for the name to the left of the function-call operator, it inhibits argument-dependent lookup.

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 of the elements of a vector of ints first to -1, then to 10.

Run this code

#include <algorithm>
#include <vector>
#include <iostream>
 
int main()
{
    std::vector<int> v{0, 1, 2, 3, 4, 5, 6, 7, 8, 9};
 
    namespace ranges = std::ranges;
    ranges::fill(v.begin(), v.end(), -1);
 
    for (auto elem : v) {
        std::cout << elem << " ";
    }
    std::cout << "\n";
 
    ranges::fill(v, 10);
 
    for (auto elem : v) {
        std::cout << elem << " ";
    }
    std::cout << "\n";
}

Output:

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

Compiler support
Freestanding and hosted
Language
Standard library headers
Named requirements
Feature test macros (C++20)
Language support library
Concepts library (C++20)
Metaprogramming library (C++11)
Diagnostics library
General utilities library
Strings library
Containers library
Iterators library
Ranges library (C++20)
Algorithms library
Numerics library
Localizations library
Input/output library
Filesystem library (C++17)
Regular expressions library (C++11)
Concurrency support library (C++11)
Technical specifications
Symbols index
External libraries

ranges::fill_n (C++20)	assigns a value to a number of elements (niebloid)
ranges::copyranges::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)