The alignas type specifier is a portable, C++ standard way to specify custom alignment of variables and user defined types. The alignof operator is likewise a standard, portable way to obtain the alignment of a specified type or variable.
You can use alignas on a class, struct or union, or on individual members. When multiple alignas specifiers are encountered, the compiler will choose the strictest one, (the one with the largest value).
// alignas_alignof.cpp
// compile with: cl /EHsc alignas_alignof.cpp
#include <iostream>
struct alignas(16) Bar
{
int i; // 4 bytes
int n; // 4 bytes
alignas(4) char arr[3];
short s; // 2 bytes
};
int main()
{
std::cout << alignof(Bar) << std::endl; // output: 16
}