std::get_temporary_buffer(3)

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>)