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std::ranges::fill_n

From cppreference.com
< cpp‎ | algorithm‎ | ranges
 
 
Algorithm library
Constrained algorithms and algorithms on ranges (C++20)
Constrained algorithms, e.g. std::ranges::copy, std::ranges::sort, ...
Execution policies (C++17)
Non-modifying sequence operations
(C++11)(C++11)(C++11)
(C++17)
Modifying sequence operations
Partitioning operations
Sorting operations
(C++11)
Binary search operations
Set operations (on sorted ranges)
Heap operations
(C++11)
Minimum/maximum operations
(C++11)
(C++17)

Permutations
Numeric operations
Operations on uninitialized storage
(C++17)
(C++17)
(C++17)
C library
 
Constrained algorithms
Non-modifying sequence operations
Modifying sequence operations
Partitioning operations
Sorting operations
Binary search operations
Set operations (on sorted ranges)
Heap operations
Minimum/maximum operations
Permutations
Operations on uninitialized storage
Return types
 
Defined in header <algorithm>
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)

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

The function-like entities described on this page are niebloids, that is:

In practice, they may be implemented as function objects, or with special compiler extensions.

Contents

[edit] Parameters

first - the beginning of the range of elements to modify
n - number of elements to modify
value - the value to be assigned

[edit] Return value

An output iterator that compares equal to first + n.

[edit] Complexity

Exactly n assignments.

[edit] Possible implementation

struct fill_n_fn {
  template<class T, std::output_iterator<const T&> O>
    constexpr O operator()(O first, std::iter_difference_t<O> n, const T& value) const {
      for (std::iter_difference_t<O> i{}; i != n; *first = value, ++first, ++i);
      return first;
    }
};
 
inline constexpr fill_n_fn fill_n{};

[edit] Example

#include <algorithm>
#include <iostream>
#include <string>
#include <vector>
 
auto print(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, "░░");
    print(v);
 
    std::ranges::fill_n(v.begin(), n, "▓▓");
    print(v);
}

Output:

░░ ░░ ░░ ░░ ░░ ░░ ░░ ░░
▓▓ ▓▓ ▓▓ ▓▓ ▓▓ ▓▓ ▓▓ ▓▓

[edit] See also

assigns a range of elements a certain value
(niebloid) [edit]
copies a number of elements to a new location
(niebloid) [edit]
saves the result of a function in a range
(niebloid) [edit]
applies a function to a range of elements
(niebloid) [edit]
copy-assigns the given value to N elements in a range
(function template) [edit]