_Alignof operator
From cppreference.com
Queries the alignment requirement of its operand type.
Syntax
_Alignof( type-name )
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(since C11) | ||||||||
This operator is typically used through the convenience macro alignof, which is provided in the header stdalign.h
Explanation
Returns the alignment requirement of the type named by type-name. If type-name is an array type, the result is the alignment requirement of the array element type. The type-name cannot be function type or an incomplete type.
The result is an integer constant of type size_t.
The operand is not evaluated (so external identifiers used in the operand do not have to be defined)
Notes
The use of alignof with expressions is allowed by some C compilers as a non-standard extension.