[teo_zero]

It's not that simple!

To begin with, sizeof has two syntaxes: the first, which is the one you seem to refer to, is simply

  sizeof expression

where expression involves variables and constants, not types. The second is

  sizeof (type)

where the parentheses are mandatory.

Then, even in the first syntax, even if sizeof is listed among the operators, even if it doesn't look any different from "pointer operator ", nonetheless it has strange priority rules. For example

  sizeof (T) *x

If it was a regular prefix operator obeying priority and right-to-left evaluation, this would mean: dereference x, cast it to T, and return its size. Instead the C standard forces the compiler to interpret it as: take the size of type T and multiply it by x.