std::ranges::fill
From cppreference.com
| Defined in header <algorithm>
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| Call signature |
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template< class T, std::output_iterator<const T&> O, std::sentinel_for<O> S >
constexpr O fill( O first, S last, const T& value );
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(1) | (since C++20) (until C++26) |
template< class O, std::sentinel_for<O> S, class T = std::iter_value_t<O> >
requires std::output_iterator<O, const T&>
constexpr O fill( O first, S last, const T& value );
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(since C++26) | |
template< class T, ranges::output_range<const T&> R >
constexpr ranges::borrowed_iterator_t<R> fill( R&& r, const T& value );
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(2) | (since C++20) (until C++26) |
template< class R, class T = ranges::range_value_t<R> >
requires ranges::output_range<R, const T&>
constexpr ranges::borrowed_iterator_t<R> fill( R&& r, const T& value );
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(since C++26) | |
template< /*execution-policy*/ Ep,
std::random_access_iterator O, std::sized_sentinel_for<O> S,
class T = std::iter_value_t<O> >
requires std::indirectly_writable<O, const T&>
O fill( Ep&& policy, O first, S last, const T& value );
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(3) | (since C++26) |
template< /*execution-policy*/ Ep,
/*sized-random-access-range*/ R,
class T = ranges::range_value_t<R> >
requires std::indirectly_writable<ranges::iterator_t<R>, const T&>
ranges::borrowed_iterator_t<R> fill( Ep&& policy, R&& r, const T& value );
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(4) | (since C++26) |
For the definition of /*execution-policy*/, see this page; for the definition of /*sized-random-access-range*/, see this page.
1,2) Assigns
value to all elements in the target range [first, last) or r.3,4) Same as (1,2), but executed according to
policy.The function-like entities described on this page are algorithm function objects (informally known as 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.
Parameters
| first, last | - | the pair of iterators defining the target range |
| r | - | the target range |
| value | - | the value to be assigned |
| policy | - | the execution policy to use |
Return value
The past-the-end iterator of the source range.
Complexity
Given N as ranges::distance(first, last) or ranges::distance(r):
1-4) Exactly N assignments.
Exceptions
3,4) During the execution process:
- If the temporary memory resources required for parallelization are not available, std::bad_alloc is thrown.
- If an uncaught exception is thrown while accessing objects via an algorithm argument, the behavior is determined by the execution policy (for standard policies, std::terminate is invoked).
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 = ranges::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);
}
template<ranges::forward_range R, class T = ranges::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::next(ranges::begin(r), ranges::end(r)),
value);
}
};
inline constexpr fill_fn fill;
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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
| copy-assigns the given value to every element in a range (function template) | |
(C++20) |
assigns a value to a number of elements (algorithm function object) |
(C++20)(C++20) |
copies a range of elements to a new location (algorithm function object) |
(C++20) |
saves the result of a function in a range (algorithm function object) |
(C++20) |
applies a function to a range of elements (algorithm function object) |
(C++26) |
fills a range with random numbers from a uniform random bit generator (algorithm function object) |