std::get_temporary_buffer

Header: <memory>

If count is negative or zero, does nothing.

# Declarations

template< class T >
std::pair<T*, std::ptrdiff_t>
get_temporary_buffer( std::ptrdiff_t count );

(until C++11)

template< class T >
std::pair<T*, std::ptrdiff_t>
get_temporary_buffer( std::ptrdiff_t count ) noexcept;

(since C++11) (deprecated in C++17) (removed in C++20)

# 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.

# 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

#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);
}

# Defect reports

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