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The sizeof operator yields the size (in bytes) of its operand, which may be an expression or the parenthesized name of a type. In most cases, the operand is not evaluated. A possible exception is when the type of the operand is a variable length array type (VLA) the expression is evaluated. When part of the operand of the sizeof operator is a VLA type and when changing the value of the VLA's size expression would not affect the result of the operator, it is unspecified whether or not the size expression is evaluated . See (see unspecified behavior 22 in Annex J of the C Standard).
The operands passed to _Generic and _Alignof are never evaluated.
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