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Page history last edited by Kenneth Finnegan 14 years, 6 months ago

I use this trick a lot to see how many times a function is called or what section of code a segmentation fault came from.  The useful part about this trick is that once all the messages are in the code, them being compiled into the program is optional.



#ifdef DEBUG

#define ErR(a) fprintf(stderr, "%s\n", a)


#define ErR(a) NULL




// hello.c

main() {

     ErR("Beginning of main");

     printf("Hello World!\n");

     ErR("End of main");



Compile with:

cc -o hello hello.c -DDEBUG

The -D flag defines the symbol after it, so ErR gets replaced with fprintf only if DEBUG is defined, otherwise it disappears.



If the debug messages are going by too fast, you can add in a second clause for DEBUG_SLOW being defined to pause 1 seconds after each message

#if defined DEBUG

#define ErR(a) fprintf(stderr, "%s\n", a)

#elif defined DEBUG_SLOW

#define ErR(a) fprintf(stderr, "%s\n", a); sleep(1)


#define ErR(a) NULL



If you want something more general than just printing messages, you can instead do:

#ifdef DEBUG

#define IF_DEBUG(a) (a)


#define IF_DEBUG(a) NULL



For a very good outline on how to have the program also display which file and which line in the file the message was from, read this article.





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