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

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.)

Answer 2

If you're a Linux user and you also use GNOME then I would have to recommend GEdit. I really loved it after I installed some plugins for Intellisense, file browsing, etc... If you're not running GNOME but are still using Linux (KDE) you might be able to use Kate. I didn't play with it for too long so I don't have much to say about that. GEdit will work in KDE but it won't look right.

If you're using Windows and have a really good PC then try Netbeans (yeah it's for C++ also, not just Java). If not there's always Visual C++ 2008 (still pretty RAM dependent though).

I'm not sure about Mac as I can't afford one, but Netbeans works on it also (as well as Linux).

Answer 3

Consider looking at "Son of Unifdef", cited in the answer to Is there a C pre-processor which eliminates #ifdef blocks based on values defined/undefined?. This isn't a visual editor - it would, however, take C code (or code with C preprocessor directives in it) and generate a modified file which you could then compare with the original.

I'm curious about the mention of Informix 4GL (I4GL). The C code it generates is not, AFAIK, laced with #ifdef constructs. At least, the output was not allowed to contain any when I was in charge of it. (Which version of I4GL are you using?) There are lots of #line entries; those permit you to chase the generated code back to the corresponding I4GL source. I have a script that converts those into simple C comments so that I can use a debugger (gdb or dbx or ... perish the thought, sdb or adb) on the compiled code. And I have also seen preprocessors (both cpp and m4) used to generate I4GL source code for submission to the I4GL compiler.

Answer 4

Emacs has hide-ifdef-mode (I've never had to use it myself, so I can't vouch for its quality)

Answer 5

You can also try unifdef which is rather simpler than sunifdef.