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std::allocator::allocate(3) C++ Standard Libary std::allocator::allocate(3) NAME std::allocator::allocate - std::allocator::allocate Synopsis pointer allocate( size_type n, const void* (until C++17) hint = 0 ); T* allocate( std::size_t n, const void* (since C++17) hint ); (deprecated) (1) (removed in C++20) T* allocate( std::size_t n ); (since C++17) (2) (until C++20) [[nodiscard]] constexpr T* allocate( (since C++20) std::size_t n ); Allocates n * sizeof(T) bytes of uninitialized storage by calling ::operator new(std::size_t) or ::operator new(std::size_t, std::align_val_t) (since C++17), but it is unspecified when and how this function is called. The pointer hint may be used to provide locality of reference: the allo- cator, if supported by the implementation, will attempt to allocate the new memory block as close as possible to hint. Then, this function creates an array of type T[n] in the storage and starts its lifetime, but does not start lifetime of any of its elements. Use of this function is ill-formed if T is an incomplete type. In order to use this function in a constant expression, the allo- cated storage must be deallocated within the evaluation of the same (since C++20) expression. Parameters n - the number of objects to allocate storage for hint - pointer to a nearby memory location Return value Pointer to the first element of an array of n objects of type T whose elements have not been constructed yet. Exceptions Throws std::bad_array_new_length if (since C++11) std::numeric_limits<std::size_t>::max() / sizeof(T) < n. Throws std::bad_alloc if allocation fails. Notes The "unspecified when and how" wording makes it possible to combine or optimize away heap allocations made by the standard library containers, even though such optimizations are disallowed for direct calls to ::operator new. For example, this is implemented by libc++ ([1] and [2]). After calling allocate() and before construction of elements, pointer arithmetic of T* is well-defined within the allocated array, but the behavior is undefined if elements are accessed. Defect reports The following behavior-changing defect reports were applied retroac- tively to previously published C++ standards. DR Applied to Behavior as published Correct behavior hint was required to be either 0 or a LWG 578 C++98 pointer previously returned not required from allocate() and not yet passed to deallocate() LWG 3190 C++11 allocate() might allocate throws std::bad_array_new_length storage of wrong size instead See also allocate allocates uninitialized storage using the allocator [static] (public static member function of std::allocator_traits<Al- loc>) http://cppreference.com 2024.06.10 std::allocator::allocate(3)
NAME | Synopsis | Parameters | Return value | Exceptions | Notes | See also
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