lvalue required as unary ‘&’ operand

Question

I have the following lines of code :

#define PORT 9987

and

char *ptr = (char *)&PORT;

This seems to work in my server code. But as I wrote it in my client code, it gives this error message :

lvalue required as unary ‘&’ operand

What am I doing wrong?

Answer 1

C preprocessor is at play here. After the code is preprocessed, this how it looks like.

char *ptr = (char *)&9987;

address of ( & ) operator can be applied to a variable and not a literal.

Answer 2

The preprocessor macros have no memory and at compile time the macro is replaced with the value. So actualy thing happening here is char *ptr = (char *)&9987 ;, which is not possible.