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

Sizeof analyzes the passed expression to find its type. It then returns the size of the type.

Because the size of a type is always known at compile time, it is put into the machine code as a constant.