what's the mechanism of sizeof() in C/C++?

Question

It seems sizeof is not a real function?

for example, if you write like this:

int i=0;
printf(\"%d\\n\", sizeof(++i));
printf(\"%d\\n\", i);
         


        

Answer 1

You said it yourself: 'sizeof' is not a function. It is a built-in operator with special syntax and semantics (see the previous responses). To remember better that it is not a function, you might want to get rid of the habit to use superfluous braces and prefer to use the "braceless" 'sizeof' with expressions as in the following example

printf("%d\n", sizeof ++i);

This is exactly equivalent to your original version.