std::alloca...te_at_least(3) C++ Standard Libary std::alloca...te_at_least(3) NAME std::allocator_traits::allocate_at_least - std::allocator_traits::allo- cate_at_least Synopsis [[nodiscard]] static constexpr std::allocation_result<pointer, size_type> (since C++23) allocate_at_least( Alloc& a, size_type n ); allocate_at_least calls a.allocate_at_least(n) and returns its result if the call is well-formed, otherwise, it is equivalent to return {a.allocate(n), n};. allocator_at_least tries to allocate a storage for at least n value_type objects, and provides a fallback mechanism that allocates a storage for exact n objects. Parameters a - an allocator used for allocating storage n - the lower bound of number of objects to allocate storage for Return value a.allocate_at_least(n) if it is well-formed. Otherwise, std::allocation_result<pointer, size_type>{a.allocate(n), n}. Exceptions Throws what and when the selected allocation function throws. Notes The allocate_at_least member function of Allocator types are mainly pro- vided for contiguous containers, e.g. std::vector and std::basic_string, in order to reduce reallocation by making their capacity match the actually allocated size when possible. Because allocate_at_least provides a fallback mechanism, it can be directly used where appropriate. Given an allocator object a of type Alloc, let result denote the value returned from std::allocator_traits<Alloc>::allocate_at_least(a, n), the storage should be deallocated by a.deallocate(result.ptr, m) (typically called via std::allocator_traits<Alloc>::deallocate(a, result.ptr, m)) in order to avoid memory leak. The argument m used in deallocation must be not less than n and not greater than result.count, otherwise, the behavior is undefined. Note that n is al- ways equal to result.count if the allocator does not provide allocate_at_least, which means that m is required to be equal to n. Feature-test macro Value Std Feature __cpp_lib_allocate_at_least 202302L (C++23) allocate_at_least etc. Example This section is incomplete Reason: no example See also allocate_at_least allocates uninitialized storage at least as large as requested (C++23) size (public member function of std::allocator<T>) Category: * Todo no example http://cppreference.com 2024.06.10 std::alloca...te_at_least(3)
NAME | Synopsis | Parameters | Return value | Exceptions | Notes | Example | See also | Category:
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