Using sizeof operator on a typedef-ed struct

Question

This might be something too obvious. However, I couldn\'t find the specific answer though many stackoverflow threads talk about different aspects of this.

typede         


        

Answer 1

add parentheses around tmp: sizeof(tmp)

Answer 2

The sizeof operator have two forms:

sizeof expression
sizeof(type)

As you're giving it a type, you need the parenthesis, sizeof(tmp)

Answer 3

5.3.3 Sizeof [expr.sizeof]

1) The sizeof operator yields the number of bytes in the object representation of its operand. The operand is either an expression, which is an unevaluated operand (Clause 5), or a parenthesized type-id. (emphasis mine)

In your case, it is a type-id so it must be parenthesized. What a type-id is is described in 8.1 Type names [dcl.name].

sizeof tmp should be sizeof (tmp).

As in

if (c <= sizeof tmp) should be if (c <= sizeof (tmp)).

Yup, pretty "obvious and straightforward".