#define macro for debug printing in C?

So, when using gcc, I like:

#define DBGI(expr) ({int g2rE3=expr; fprintf(stderr, "%s:%d:%s(): ""%s->%i\n", __FILE__,  __LINE__, __func__, #expr, g2rE3); g2rE3;})

Because it can be inserted into code.

Suppose you're trying to debug

printf("%i\n", (1*2*3*4*5*6));

720

Then you can change it to:

printf("%i\n", DBGI(1*2*3*4*5*6));

hello.c:86:main(): 1*2*3*4*5*6->720
720

And you can get an analysis of what expression was evaluated to what.

It's protected against the double-evaluation problem, but the absence of gensyms does leave it open to name-collisions.

However it does nest:

DBGI(printf("%i\n", DBGI(1*2*3*4*5*6)));

hello.c:86:main(): 1*2*3*4*5*6->720
720
hello.c:86:main(): printf("%i\n", DBGI(1*2*3*4*5*6))->4

So I think that as long as you avoid using g2rE3 as a variable name, you'll be OK.

Certainly I've found it (and allied versions for strings, and versions for debug levels etc) invaluable.

#define PRINT_LOG(str_format, ...) { \
    time_t curtime=time (NULL); \
    struct tm *ltm = localtime (&curtime); \
    printf("[%d-%02d-%02d %02d:%02d:%02d] " str_format, \
        ltm->tm_year + 1900, ltm->tm_mon + 1, ltm->tm_mday, \
        ltm->tm_hour, ltm->tm_min, ltm->tm_sec, ##__VA_ARGS__); \
}
    
PRINT_LOG("[%d] Serving client, str=%s, number=%d\n", getpid(), "my str", 10);

If you don't care that the output goes to stdout, you can use this:

int doDebug = DEBUG;  // Where DEBUG may be supplied in compiler command
#define trace if (doDebug) printf

trace("whatever %d, %i\n", arg1, arg2);