cppreference std::max_align_t

Notes

Pointers returned by allocation functions such as std::malloc are suitably aligned for any object, which means they are aligned at least as strictly as std::max_align_t.

std::max_align_t is usually synonymous with the largest scalar type, which is long double on most platforms, and its alignment requirement is either 8 or 16.

stackoverflow Order between STDCPP_DEFAULT_NEW_ALIGNMENT and alignof(std::max_align_t)

With GCC and Clang on x86-64/Linux alignof(std::max_align_t) and __STDCPP_DEFAULT_NEW_ALIGNMENT__ are both equal to 16.

With MSVC on x86-64/Windows alignof(std::max_align_t) is 8 and __STDCPP_DEFAULT_NEW_ALIGNMENT__ is 16.

The standard defines the two terms corresponding to these quantities in [basic.align]/3:

An extended alignment is represented by an alignment greater than alignof(std::max_­align_­t). [...] A type having an extended alignment requirement is an over-aligned type. [...] A new-extended alignment is represented by an alignment greater than _­_­STDCPP_­DEFAULT_­NEW_­ALIGNMENT_­_­.

A

1、std::max_align_t: The alignment of the biggest scalar type

2、__STDCPP_DEFAULT_NEW_ALIGNMENT__: The alignment of allocated memory

NOTE:

C++17引入