std::get_temporary_buffer
Defined in header <memory>
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template< class T > std::pair<T*, std::ptrdiff_t> |
(until C++11) | |
template< class T > std::pair<T*, std::ptrdiff_t> |
(since C++11) (deprecated in C++17) (removed in C++20) |
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If count is negative or zero, does nothing.
Otherwise, requests to allocate uninitialized contiguous storage for count adjacent objects of type T
. The request is non-binding, and the implementation may instead allocate the storage for any other number of (including zero) adjacent objects of type T
.
It is implementation-defined whether over-aligned types are supported. |
(since C++11) |
Contents |
[edit] Parameters
count | - | the desired number of objects |
[edit] Return value
A std::pair, the member first
is a pointer to the beginning of the allocated storage and the member second
is the number of objects that fit in the storage that was actually allocated.
If count <= 0 or allocated storage is not enough to store a single element of type T
, the member first
of the result is a null pointer and the member second
is zero.
[edit] Notes
This API was originally designed with the intent of providing a more efficient implementation than the general-purpose operator new, but no such implementation was created and the API was deprecated and removed.
[edit] Example
#include <algorithm> #include <iostream> #include <iterator> #include <memory> #include <string> int main() { const std::string s[] = {"string", "1", "test", "..."}; const auto p = std::get_temporary_buffer<std::string>(4); // requires that p.first is passed to return_temporary_buffer // (beware of early exit points and exceptions), or better use: std::unique_ptr<std::string, void(*)(std::string*)> on_exit(p.first, [](std::string* p) { std::cout << "returning temporary buffer...\n"; std::return_temporary_buffer(p); }); std::copy(s, s + p.second, std::raw_storage_iterator<std::string*, std::string>(p.first)); // has same effect as: std::uninitialized_copy(s, s + p.second, p.first); // requires that each string in p is individually destroyed // (beware of early exit points and exceptions) std::copy(p.first, p.first + p.second, std::ostream_iterator<std::string>{std::cout, "\n"}); std::for_each(p.first, p.first + p.second, [](std::string& e) { e.~basic_string<char>(); }); // same as: std::destroy(p.first, p.first + p.second); // manually reclaim memory if unique_ptr-like technique is not used: // std::return_temporary_buffer(p.first); }
Output:
string 1 test ... returning temporary buffer...
[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 425 | C++98 | the behavior when count <= 0 was unclear | made clear |
LWG 2072 | C++98 | it was not allowed to allocate insufficient memory | allowed |
[edit] See also
(deprecated in C++17)(removed in C++20) |
frees uninitialized storage (function template) |
[static] (C++23) |
allocates storage at least as large as the requested size via an allocator (public static member function of std::allocator_traits<Alloc> )
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