std::uninitialized_fill
From cppreference.com
C++
Feature test macros (C++20)
Concepts library (C++20)
Metaprogramming library (C++11)
Ranges library (C++20)
Filesystem library (C++17)
Concurrency support library (C++11)
Execution control library (C++26)
Memory management library
Uninitialized memory algorithms
Constrained uninitialized memory algorithms
Memory resources
Uninitialized storage (until C++20)
Garbage collector support (until C++23)
(exposition only*)
(C++11)
(C++23)
(C++11)
(C++17)
(C++11)
(C++11)
(C++20)
(C++20)
uninitialized_fill
(C++17)
(C++11)
(C++17)
(C++20)
(C++17)
(C++17)
(C++17)
(C++17)
(C++17)
(C++17)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++17)
(C++17)
(C++17)
(C++17)
(C++17)
(C++17)
(C++17)
(C++17)
(until C++20*)
(until C++20*)
(until C++20*)
(C++11)(until C++23)
(C++11)(until C++23)
(C++11)(until C++23)
(C++11)(until C++23)
(C++11)(until C++23)
(C++11)(until C++23)
(C++11)
(C++11)
(C++17)
(C++20)
(C++17)
(C++11)
(C++11)
(C++11)
(until C++17*)
(C++11)
(C++17)
(C++26)
(C++26)
(C++11)
(C++11)
(C++11)
(C++23)
(C++23)
(C++11)
(C++20)
(C++11)
(C++11)
(C++20)
(C++26)
Defined in header
<memory>
template< class NoThrowForwardIt, class T >
(1)
(constexpr since C++26)
void uninitialized_fill( NoThrowForwardIt first,
template< class ExecutionPolicy, class NoThrowForwardIt, class T >
(2)
(since C++17)
void uninitialized_fill( ExecutionPolicy&& policy,
NoThrowForwardIt first,
1) Copies value to an uninitialized memory area
[first, last) as if by
for (; first != last; ++first)
::new (voidify (*first))
typename std::iterator_traits <NoThrowForwardIt>::value_type(value);
If an exception is thrown during the initialization, the objects already constructed are destroyed in an unspecified order.
2) Same as (1), but executed according to policy.
This overload participates in overload resolution only if all following conditions are satisfied:
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, last
-
the pair of iterators defining the range of elements to initialize
value
-
the value to construct the elements with
policy
-
the execution policy to use
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] Complexity
Linear in the distance between first and last.
[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
ExecutionPolicyis 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 T> constexpr void uninitialized_fill(NoThrowForwardIt first, NoThrowForwardIt last, const T& value) { using V = typename std::iterator_traits <NoThrowForwardIt>::value_type; NoThrowForwardIt current = first; try { for (; current != last; ++current) ::new (static_cast<void*>(std::addressof (*current))) V(value); } catch (...) { for (; first != current; ++first) first->~V(); throw; } }
[edit] Example
Run this code
#include <algorithm> #include <iostream> #include <memory> #include <string> int main() { const std::size_t sz = 4; std::allocator <std::string > alloc; std::string * p = alloc.allocate(sz); std::uninitialized_fill(p, p + sz, "Example"); for (std::string * i = p; i != p + sz; ++i) { std::cout << *i << '\n'; i->~basic_string<char>(); } alloc.deallocate(p, sz); }
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 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 start and a count
(function template) [edit]
(function template) [edit]
(C++20)
(algorithm function object)[edit]