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]