refactoring - Ways to ASSERT expressions at build time in C

Question

I'm tidying up some older code that uses 'magic numbers' all over the place to set hardware registers, and I would like to use constants instead of these numbers to make the code somewhat more expressive (in fact they will map to the names/values used to document the registers).

However, I'm concerned that with the volume of changes I might break the magic numbers. Here is a simplified example (the register set is more complex):

const short mode0 = 0;
const short mode1 = 1;
const short mode2 = 2;

const short state0 = 0;
const short state1 = 4;
const short state2 = 8;

so instead of :

set_register(5);

we have:

set_register(state1|mode1);

What I'm looking for is a build time version of:

ASSERT(5==(state1|mode1));

Update

@Christian, thanks for the quick response, I'm interested on a C / non-boost environment answer too because this is driver/kernel code.

Answer 1

NEW ANSWER :

In my original answer (below), I had to have two different macros to support assertions in a function scope and at the global scope. I wondered if it was possible to come up with a single solution that would work in both scopes.

I was able to find a solution that worked for Visual Studio and Comeau compilers using extern character arrays. But I was able to find a more complex solution that works for GCC. But GCC's solution doesn't work for Visual Studio. :( But adding a '#ifdef __ GNUC __', it's easy to choose the right set of macros for a given compiler.

Solution:

#ifdef __GNUC__
#define STATIC_ASSERT_HELPER(expr, msg) 
    (!!sizeof  (struct { unsigned int STATIC_ASSERTION__##msg: (expr) ? 1 : -1; }))
#define STATIC_ASSERT(expr, msg) 
    extern int (*assert_function__(void)) [STATIC_ASSERT_HELPER(expr, msg)]
#else
    #define STATIC_ASSERT(expr, msg)   
    extern char STATIC_ASSERTION__##msg[1]; 
    extern char STATIC_ASSERTION__##msg[(expr)?1:2]
#endif /* #ifdef __GNUC__ */

Here are the error messages reported for STATIC_ASSERT(1==1, test_message); at line 22 of test.c:

GCC:

line 22: error: negative width in bit-field `STATIC_ASSERTION__test_message'

Visual Studio:

test.c(22) : error C2369: 'STATIC_ASSERTION__test_message' : redefinition; different subscripts
    test.c(22) : see declaration of 'STATIC_ASSERTION__test_message'

Comeau:

line 22: error: declaration is incompatible with
        "char STATIC_ASSERTION__test_message[1]" (declared at line 22)

 
 

ORIGINAL ANSWER :

I do something very similar to what Checkers does. But I include a message that'll show up in many compilers:

#define STATIC_ASSERT(expr, msg)               
{                                              
    char STATIC_ASSERTION__##msg[(expr)?1:-1]; 
    (void)STATIC_ASSERTION__##msg[0];          
}

And for doing something at the global scope (outside a function) use this:

#define GLOBAL_STATIC_ASSERT(expr, msg)   
  extern char STATIC_ASSERTION__##msg[1]; 
  extern char STATIC_ASSERTION__##msg[(expr)?1:2]