std::uninitialized_copy
From cppreference.com
| Defined in header <memory>
|
||
template< class InputIt, class NoThrowForwardIt >
NoThrowForwardIt uninitialized_copy( InputIt first, InputIt last,
NoThrowForwardIt d_first );
|
(1) | (constexpr since C++26) |
template< class ExecutionPolicy, class ForwardIt,
class NoThrowForwardIt >
NoThrowForwardIt uninitialized_copy( ExecutionPolicy&& policy,
ForwardIt first, ForwardIt last,
NoThrowForwardIt d_first );
|
(2) | (since C++17) |
1) Constructs elements in the destination range beginning at
d_first from elements in the source range [first, last) as if by
for (; first != last; ++d_first, (void) ++first)
::new (voidify(*d_first))
typename std::iterator_traits<NoThrowForwardIt>::value_type(*first);
return d_first;
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 the value of the following expression is
true:
|
|
(until C++20) |
|
|
(since C++20) |
|
If |
(since C++20) |
Parameters
| first, last | - | the pair of iterators defining the range of elements to copy |
| d_first | - | the beginning of the destination range |
| policy | - | the execution policy to use |
| Type requirements | ||
-InputIt must meet the requirements of LegacyInputIterator.
| ||
-ForwardIt must meet the requirements of LegacyForwardIterator.
| ||
-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)
| ||
Return value
As described above.
Exceptions
2) 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).
Notes
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_raw_memory_algorithms |
202411L |
(C++26) | constexpr for specialized <memory> algorithms, (1)
|
Possible implementation
template<class InputIt, class NoThrowForwardIt>
constexpr NoThrowForwardIt uninitialized_copy(InputIt first, InputIt last,
NoThrowForwardIt d_first)
{
using T = typename std::iterator_traits<NoThrowForwardIt>::value_type;
NoThrowForwardIt current = d_first;
try
{
for (; first != last; ++first, (void) ++current)
::new (static_cast<void*>(std::addressof(*current))) T(*first);
return current;
}
catch (...)
{
for (; d_first != current; ++d_first)
d_first->~T();
throw;
}
}
|
Example
Run this code
#include <cstdlib>
#include <iostream>
#include <memory>
#include <string>
int main()
{
const char *v[] = {"This", "is", "an", "example"};
auto sz = std::size(v);
if (void *pbuf = std::aligned_alloc(alignof(std::string), sizeof(std::string) * sz))
{
try
{
auto first = static_cast<std::string*>(pbuf);
auto last = std::uninitialized_copy(std::begin(v), std::end(v), first);
for (auto it = first; it != last; ++it)
std::cout << *it << '_';
std::cout << '\n';
std::destroy(first, last);
}
catch (...) {}
std::free(pbuf);
}
}
Output:
This_is_an_example_
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 replacement- new instead |
| LWG 2133 | C++98 | the effect description used a for loop with the iterationexpression ++d_first, ++first, which resultsin an argument-dependent lookup of operator,
|
discards the value of one operand to disable that ADL |
| LWG 2433 | C++11 | this algorithm might be hijacked by overloaded operator&
|
uses std::addressof |
See also
(C++11) |
copies a number of objects to an uninitialized area of memory (function template & algorithm function object) |
(C++20) |
|
(C++20) |
copies a range of objects to an uninitialized area of memory (algorithm function object) |