std::fill
Defined in header <algorithm>
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(1) | ||
template< class ForwardIt, class T > void fill( ForwardIt first, ForwardIt last, const T& value ); |
(constexpr since C++20) (until C++26) |
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template< class ForwardIt, class T = typename std::iterator_traits <ForwardIt>::value_type > |
(since C++26) | |
(2) | ||
template< class ExecutionPolicy, class ForwardIt, class T > void fill( ExecutionPolicy&& policy, |
(since C++17) (until C++26) |
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template< class ExecutionPolicy, class ForwardIt, class T = typename std::iterator_traits |
(since C++26) | |
[
first,
last)
.
std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true. |
(until C++20) |
std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>> is true. |
(since C++20) |
If value is not writable to first, the program is ill-formed.
Contents |
[edit] Parameters
first, last | - | the range of elements to modify |
value | - | the value to be assigned |
policy | - | the execution policy to use. See execution policy for details. |
Type requirements | ||
-ForwardIt must meet the requirements of LegacyForwardIterator.
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[edit] Complexity
Exactly std::distance(first, last) assignments.
[edit] Exceptions
The overload with a template parameter named ExecutionPolicy
reports errors as follows:
- If execution of a function invoked as part of the algorithm throws an exception and
ExecutionPolicy
is one of the standard policies, std::terminate is called. For any otherExecutionPolicy
, the behavior is implementation-defined. - If the algorithm fails to allocate memory, std::bad_alloc is thrown.
[edit] Possible implementation
fill |
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template<class ForwardIt, class T = typename std::iterator_traits<ForwardIt>::value_type> void fill(ForwardIt first, ForwardIt last, const T& value) { for (; first != last; ++first) *first = value; } |
[edit] Notes
Feature-test macro | Value | Std | Feature |
---|---|---|---|
__cpp_lib_algorithm_default_value_type |
202403 |
(C++26) | List-initialization for algorithms (1,2) |
[edit] Example
#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, 6, 7, 8}; println(v); // set all of the elements to 8 std::fill(v.begin(), v.end(), 8); println(v); std::vector<std::complex<double>> nums{{1, 3}, {2, 2}, {4, 8}}; println(nums); #ifdef __cpp_lib_algorithm_default_value_type std::fill(nums.begin(), nums.end(), {4, 2}); #else std::fill(nums.begin(), nums.end(), std::complex<double>{4, 2}); #endif println(nums); }
Output:
0 1 2 3 4 5 6 7 8 8 8 8 8 8 8 8 8 8 (1,3) (2,2) (4,8) (4,2) (4,2) (4,2)
[edit] Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
DR | Applied to | Behavior as published | Correct behavior |
---|---|---|---|
LWG 283 | C++98 | T was required to be CopyAssignable, butT is not always writable to ForwardIt
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required to be writable instead |
[edit] See also
copy-assigns the given value to N elements in a range (function template) | |
(C++11) |
copies a range of elements to a new location (function template) |
assigns the results of successive function calls to every element in a range (function template) | |
applies a function to a range of elements, storing results in a destination range (function template) | |
(C++20) |
assigns a range of elements a certain value (algorithm function object) |