std::uninitialized_move_n(3) | C++ Standard Libary | std::uninitialized_move_n(3) |
NAME¶
std::uninitialized_move_n - std::uninitialized_move_n
Synopsis¶
Defined in header <memory>
template< class InputIt, class Size, class NoThrowForwardIt >
std::pair<InputIt, NoThrowForwardIt> (1) (since
C++17)
uninitialized_move_n( InputIt first, Size count, NoThrowForwardIt
d_first );
template< class ExecutionPolicy, class ForwardIt, class Size,
class NoThrowForwardIt >
std::pair<ForwardIt, NoThrowForwardIt> (2) (since C++17)
uninitialized_move_n( ExecutionPolicy&& policy, ForwardIt first,
Size count,
NoThrowForwardIt d_first );
1) Moves count elements from a range beginning at first to an uninitialized
memory
area beginning at d_first as if by
for ( ; n > 0; ++d_first, (void) ++first, --n)
::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 the
source
range 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 - the beginning of the range of the elements to move
d_first - the beginning of the destination range
count - the number of elements to move
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¶
A pair whose first element is an iterator to the element past the
last element moved
in the source range, and whose second element is an iterator to the element
past the
last element moved in the destination range.
Complexity¶
Linear in count.
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 Size, class NoThrowForwardIt>
std::pair<InputIt, NoThrowForwardIt>
uninitialized_move_n(InputIt first, Size count, NoThrowForwardIt d_first)
{
using Value = typename
std::iterator_traits<NoThrowForwardIt>::value_type;
NoThrowForwardIt current = d_first;
try {
for (; count > 0; ++first, (void) ++current, --count) {
::new (const_cast<void*>(static_cast<const volatile void*>(
std::addressof(*current)))) Value(std::move(*first));
}
} catch (...) {
std::destroy(d_first, current);
throw;
}
return {first, current};
}
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[] { "One", "Definition", "Rule"
};
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_n(std::begin(in), sz, 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: "One" "Definition"
"Rule"
after move, in: "" "" ""
after move, out: "One" "Definition" "Rule"
See also¶
uninitialized_move moves a range of objects to an uninitialized
area of
(C++17) memory
(function template)
uninitialized_copy_n copies a number of objects to an uninitialized area of
(C++11) memory
(function template)
ranges::uninitialized_move_n moves a number of objects to an uninitialized
area of
(C++20) memory
(niebloid)
2022.07.31 | http://cppreference.com |