NAME¶

std::ranges::fill - std::ranges::fill

Synopsis¶

Defined in header <algorithm>
Call signature
template< class T, std::output_iterator<const
T&> O, std::sentinel_for<O> S > (since C++20)
constexpr O fill( O first, S last, const T& (until C++26)
value );
template< class O, std::sentinel_for<O> S, class
T = std::iter_value_t<O> >

requires std::output_iterator<O, const T&> (since C++26)

constexpr O fill( O first, S last, const T&
value ); (1)
template< class T, ranges::output_range<const
T&> R > (since C++20)
constexpr ranges::borrowed_iterator_t<R> fill( (until C++26)
R&& r, const T& value );
template< class R, class T =
std::range_value_t<R> > (2)

requires ranges::output_range<R, const T&> (since C++26)

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

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 O, std::sentinel_for<O> S, class T = std::iter_value_t<O>>
requires std::output_iterator<O, const T&>
constexpr O operator()(O first, S last, const T& value) const
{
while (first != last)
*first++ = value;

return first;
}

template<class R, class T = std::range_value_t<R>>
requires ranges::output_range<R, const T&>
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;

Notes¶

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

Example¶

// Run this code

#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);
}

Output:¶

-1 -1 -1 -1 -1 -1
10 10 10 10 10 10
(1,3) (2,2) (4,8)
(4,2) (4,2) (4,2)

See also¶

ranges::fill_n assigns a value to a number of elements
(C++20) (niebloid)
ranges::copy
ranges::copy_if copies a range of elements to a new location
(C++20) (niebloid)
(C++20)
ranges::generate saves the result of a function in a range
(C++20) (niebloid)
ranges::transform applies a function to a range of elements
(C++20) (niebloid)
ranges::generate_random fills a range with random numbers from a uniform random bit
(C++26) generator
(niebloid)
fill copy-assigns the given value to every element in a range
(function template)