std::uninitialized_fill_n
Defined in header <memory>
|
||
template< class NoThrowForwardIt, class Size, class T > NoThrowForwardIt uninitialized_fill_n( NoThrowForwardIt first, |
(1) | (constexpr since C++26) |
template< class ExecutionPolicy, class NoThrowForwardIt, class Size, class T > |
(2) | (since C++17) |
+
[
0,
count)
as if by
for (; count--; ++first)
::new (voidify
(*first))
typename std::iterator_traits<NoThrowForwardIt>::value_type(value);
return first;
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) |
Contents |
[edit] Parameters
first | - | the beginning of the range of the elements to initialize |
count | - | number of elements to construct |
value | - | the value to construct the elements with |
Type requirements | ||
-NoThrowForwardIt must meet the requirements of LegacyForwardIterator.
| ||
-No increment, assignment, comparison, or indirection through valid instances of NoThrowForwardIt may throw exceptions. Applying &* to a NoThrowForwardIt value must yield a pointer to its value type.(until C++11)
|
[edit] Return value
As described above.
[edit] Complexity
Linear in count.
[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] Notes
Feature-test macro | Value | Std | Feature |
---|---|---|---|
__cpp_lib_raw_memory_algorithms |
202411L |
(C++26) | constexpr for specialized memory algorithms, (1) |
[edit] Possible implementation
template<class NoThrowForwardIt, class Size, class T> constexpr NoThrowForwardIt uninitialized_fill_n(NoThrowForwardIt first, Size count, const T& value) { using V = typename std::iterator_traits<NoThrowForwardIt>::value_type; NoThrowForwardIt current = first; try { for (; count > 0; ++current, (void) --count) ::new (static_cast<void*>(std::addressof(*current))) V(value); return current; } catch (...) { for (; first != current; ++first) first->~V(); throw; } return current; } |
[edit] Example
#include <algorithm> #include <iostream> #include <memory> #include <string> #include <tuple> int main() { std::string* p; std::size_t sz; std::tie(p, sz) = std::get_temporary_buffer<std::string>(4); std::uninitialized_fill_n(p, sz, "Example"); for (std::string* i = p; i != p + sz; ++i) { std::cout << *i << '\n'; i->~basic_string<char>(); } std::return_temporary_buffer(p); }
Output:
Example Example Example Example
[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 866 | C++98 | given T as the value type of NoThrowForwardIt , ifT::operator new exists, the program might be ill-formed |
uses global placement new instead |
LWG 1339 | C++98 | the location of the first element following the filling range was not returned |
returned |
LWG 2433 | C++11 | this algorithm might be hijacked by overloaded operator& | uses std::addressof |
LWG 3870 | C++20 | this algorithm might create objects on a const storage | kept disallowed |
[edit] See also
copies an object to an uninitialized area of memory, defined by a range (function template) | |
(C++20) |
copies an object to an uninitialized area of memory, defined by a start and a count (algorithm function object) |