NAME¶

std::get_temporary_buffer - std::get_temporary_buffer

Synopsis¶

Defined in header <memory>
template< class T >

std::pair<T*, std::ptrdiff_t> (until C++11)

get_temporary_buffer( std::ptrdiff_t count );
template< class T >
(since C++11)
std::pair<T*, std::ptrdiff_t> (deprecated in C++17)
(removed in C++20)
get_temporary_buffer( std::ptrdiff_t count ) noexcept;

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)

Parameters¶

count - the desired number of objects

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.

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.

Example¶

// Run this code

#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...

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 allowed
memory

See also¶

return_temporary_buffer frees uninitialized storage
(deprecated in C++17) (function template)
(removed in C++20)
allocates storage at least as large as the requested size
allocate_at_least via an allocator
[static] (C++23) (public static member function of
std::allocator_traits<Alloc>)