Is there any cure for the preprocessor blues?

Question

I know that I can kick the the preprocessor to spit out output with the -E option in my particular circumstance. For generated code this preprocessor output is murderous. For example I have a 4gl application and Informix converts this into C which in turn gets spit out to a horrible ugly mess.

What I want is an editor that will allow me to specify what preprocessor values are in effect and show me only the relevant code. I have something very basic working in Vim matching #ifdef and #endif, but the code is riddled with more advanced constructs such is #ifndef, #if, and #else. To make matters worse, the constructs are logically more complex, and I don't think my Vim scripting skills are adequate for me to get what I want out of it. For example:

#if DLEVEL > 5
    #define SIGNAL  1
    #if STACKUSE == 1
        #define STACK   200
    #else
        #define STACK   100
    #endif
#else
    #define SIGNAL  0
    #if STACKUSE == 1
        #define STACK   100
    #else
        #define STACK   50
    #endif
#endif
#if DLEVEL == 0
    #define STACK 0
#elif DLEVEL == 1
    #define STACK 100
#elif DLEVEL > 5
    display( debugptr );
#else
    #define STACK 200
#endif

Includes defining an expression evaluator if I want to tackle it. This has to be a solved problem! If you have Vim suggestions or other ones please let me know.

Answer 1

The Eclipse CDT editor does a pretty good job highlighting code based on the macros you declare to be active. You may want to check it out.

Answer 2

For an editor, Eclipse CDT works quite well. It shows which code is active and which code is #ifdef'ed out, it provides syntax highlighting within code that's #ifdef'ed out so you can still easily read it, and it can step through macro expansions one at a time if you mouse over a macro.

From the command line, cpp -dM filename.c processes a file and shows only the #defines that are in effect. For example, in your code, it might spit out

#define DLEVEL 5
#define SIGNAL 1
#define STACK 200
#define STACKUSE 1

without cluttering the listing with other preprocessor directives or with C/C++ code.

(On a related note, cpp -dM /dev/null is a handy way to find predefined macros for your platform.)