Question

This is a stupid question, but I can’t work it out and it’s beginning to irritate me!

I have the following (reg is a global):

#define CS 4
#define DS 5

unsigned char reg[6] = {0, 0, 0, 0, 0, 0x10};

Now, I would expect reg[DS] to access element 5 of array reg (0x10). However, when debugging (VC2010), Visual Studio is claiming that DS is zero and the first element is accessed. Is it me, or is Visual Studio being stupid?

Answer 1

Yes.

reg[DS] == 0x10

Unless you have redefined the macro DS somewhere else in the code.
Macros are evaluated at pre-compilation. So if you defined DS as 5 then what goes to the compiler for compilation is reg[5].

Also, You cannot check a macro value at run-time because they do not exist at run-time, they are already substituted with whatever value they are defined as.