Why isn't the result of this cast an lvalue?

Question

I need some advice with this strange behavior – lets have this code:

int ** p;

This compiles without any trouble:

p++;
         


        

Answer 1

When you typecast an expression, the result of that expression is an rvalue rather than an lvalue. Intuitively, a typecast says "give me the value that this expression would have if it had some other type," so typecasting a variable to its own type still produces an rvalue and not an lvalue. Consequently, it's not legal to apply the ++ operator to the result of a typecast, since ++ requires an lvalue and you're providing an rvalue.

That said, it is in principle possible to redefine the C language so that casting a value to its own type produces an lvalue if the original expression is an lvalue, but for simplicity's and consistency's sake I suppose the language designers didn't do this.

Hope this helps!