5.3.3 Sizeof [expr.sizeof]

1 The sizeof operator yields the number of bytes in the object represen-
tation of its operand. The operand is either an expression, which is
not evaluated, or a parenthesized type-id. The sizeof operator shall

not be applied to an expression that has function or incomplete type,
or to an enumeration type before all its enumerators have been
declared, or to the parenthesized name of such types, or to an lvalue
that designates a bit-field. sizeof(char), sizeof(signed char) and
sizeof(unsigned char) are 1; the result of sizeof applied to any other
fundamental type (_basic.fundamental_) is implementation-defined.
[Note: in particular, sizeof(bool) and sizeof(wchar_t) are
implementation-defined.15) ] [Note: See _intro.memory_ for the defini-
tion of byte and _basic.types_ for the definition of object represen-
tation. ]

2 When applied to a reference or a reference type, the result is the
size of the referenced type. When applied to a class, the result is
the number of bytes in an object of that class including any padding
required for placing objects of that type in an array. The size of a
most derived class shall be greater than zero (_intro.object_). The
result of applying sizeof to a base class subobject is the size of the
base class type.16) When applied to an array, the result is the total
number of bytes in the array. This implies that the size of an array
of n elements is n times the size of an element.

3 The sizeof operator can be applied to a pointer to a function, but
shall not be applied directly to a function.

4 The lvalue-to-rvalue (_conv.lval_), array-to-pointer (_conv.array_),
and function-to-pointer (_conv.func_) standard conversions are not
applied to the operand of sizeof.

5 Types shall not be defined in a sizeof expression.

6 The result is a constant of type size_t. [Note: size_t is defined in
the standard header <cstddef>(_lib.support.types_). ]