Java concepts in C: logging

One will always run into the problem that one needs more detailed output from a section at some time, and less verbose output at another time. Or the whole output should be more verbose, or you want to investigate a segfault.

There are some logging libraries (log4c for example). I however use the following approach:



debug.h:

#ifdef DEBUG

#define IFDEBUG if(1)

#else

#define IFDEBUG if(0)

#endif

#ifdef SEGV

#define IFSEGV if(1)

#else

#define IFSEGV if(0)

#endif

#define debug(str)        IFDEBUG { printf("\tDEBUG[%s]: %s\n", AT, str); fflush(NULL); }

#define dump_i(str, var)  IFDEBUG { printf("\tDEBUG[%s]: %s: %i\n", AT, str, var); fflush(NULL); }

#define dump_p(str, var)  IFDEBUG { printf("\tDEBUG[%s]: %s: %p\n", AT, str, var); fflush(NULL); }

in your code:

		debug("we are now doing foo ");

		IFSEGV

			dump_p("m\n", (void*)m);

		IFDEBUG

			printf("\t\tn_par=%d; status=%d\n", get_n_par(m), status);

Example output:

	DEBUG[tests/tests.c:196]: add starting points, ...

This allows you to recompile your code with -DDEBUG -DSEGV and enable/disable verbosity levels without constant code changes.

serious

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#ifndef DEBUG_H__ #define DEBUG_H__ #include <stdio.h> #ifdef DEBUG # define debugf(fmt, ...) \ fprintf(stderr, "%s:%d: %s: " fmt "\n", __FILE__, __LINE__, __func__, ##__VA_ARGS__) #else # define debugf(fmt, ...) #endif #endif

#1 by JohannesBuchner on August 1st, 2010

REPLY:
Thanks, I never got around to look at variable arguments in the preprocessor

Quote

#2 by panzi on April 18th, 2009

I prefer something like this (requires C99):

debug.h:

main.c:

#include "debug.h"
int main() {
debugf("foo %s bar %d baz %f", "...", 42, 3.1415);
return 0;
}

stderr should be unbuffered anyway, so I don’t need a fflush(stderr).

Johannes Buchner