std::get_temporary_buffer
Defined in header <memory> | ||
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) | |
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(){conststd::string s[]={"string", "1", "test", "..."};constauto 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>) |
