std::uninitialized_move(3) | C++ Standard Libary | std::uninitialized_move(3) |
NAME¶
std::uninitialized_move - std::uninitialized_move
Synopsis¶
Defined in header <memory>
template< class InputIt, class NoThrowForwardIt >
NoThrowForwardIt uninitialized_move( InputIt first, InputIt last, (1)
(since C++17)
NoThrowForwardIt d_first );
template< class ExecutionPolicy, class ForwardIt, class
NoThrowForwardIt >
NoThrowForwardIt uninitialized_move( ExecutionPolicy&& policy,
(2) (since C++17)
ForwardIt first, ForwardIt last,
NoThrowForwardIt d_first );
1) Moves elements from the range [first, last) to an uninitialized memory
area
beginning at d_first as if by
for (; first != last; ++d_first, (void) ++first)
::new (/*VOIDIFY*/(*d_first))
typename
std::iterator_traits<NoThrowForwardIt>::value_type(std::move(*first));
where /*VOIDIFY*/(e) is:
static_cast<void*>(std::addressof(e)) (until C++20)
const_cast<void*>(static_cast<const volatile (since C++20)
void*>(std::addressof(e)))
If an exception is thrown during the initialization, some objects in [first,
last)
are left in a valid but unspecified state, and the objects already
constructed are
destroyed in an unspecified order.
2) Same as (1), but executed according to policy. This overload does
not participate
in overload resolution unless
std::is_execution_policy_v<std::decay_t<ExecutionPolicy>>
(until C++20)
std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>>
(since C++20) is true.
Parameters¶
first, last - the range of the elements to move
d_first - the beginning of the destination range
policy - the execution policy to use. See execution policy for
details.
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.
Return value¶
Iterator to the element past the last element moved.
Complexity¶
Linear in the distance between first and last.
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 other ExecutionPolicy, the behavior is implementation-defined.
* If the algorithm fails to allocate memory, std::bad_alloc is thrown.
Possible implementation¶
template<class InputIt, class NoThrowForwardIt>
NoThrowForwardIt uninitialized_move(InputIt first, InputIt last,
NoThrowForwardIt d_first) {
using Value = typename
std::iterator_traits<NoThrowForwardIt>::value_type;
NoThrowForwardIt current = d_first;
try {
for (; first != last; ++first, (void) ++current) {
::new (const_cast<void*>(static_cast<const volatile void*>(
std::addressof(*current)))) Value(std::move(*first));
}
return current;
} catch (...) {
std::destroy(d_first, current);
throw;
} }
Example¶
// Run this code
#include <cstdlib>
#include <iomanip>
#include <iostream>
#include <memory>
#include <string>
void print(auto rem, auto first, auto last) {
for (std::cout << rem; first != last; ++first)
std::cout << std::quoted(*first) << ' ';
std::cout << '\n';
}
int main() {
std::string in[] { "Home", "Work!" };
print("initially, in: ", std::begin(in), std::end(in));
if (
constexpr auto sz = std::size(in);
void* out = std::aligned_alloc(alignof(std::string), sizeof(std::string) *
sz)
) {
try {
auto first {static_cast<std::string*>(out)};
auto last {first + sz};
std::uninitialized_move(std::begin(in), std::end(in), first);
print("after move, in: ", std::begin(in), std::end(in));
print("after move, out: ", first, last);
std::destroy(first, last);
}
catch (...) {
std::cout << "Exception!\n";
}
std::free(out);
}
}
Possible output:¶
initially, in: "Home" "Work!"
after move, in: "" ""
after move, out: "Home" "Work!"
See also¶
copies a range of objects to an uninitialized area of
uninitialized_copy memory
(function template)
uninitialized_move_n moves a number of objects to an uninitialized area of
(C++17) memory
(function template)
ranges::uninitialized_move moves a range of objects to an uninitialized area
of
(C++20) memory
(niebloid)
2022.07.31 | http://cppreference.com |