Is this a correct print macro?

[dspfun]

Hi,

Is the following print macro "DEBUGPRINT" ok?

// debugging macros so we can pin down message origin at a glance
#define WHERESTR "[file %s, line %d]: "
#define WHEREARG __FILE__, __LINE__
#define DEBUGPRINT2(...) fprintf(stderr, __VA_ARGS__)
#define DEBUGPRINT(_fmt, ...) DEBUGPRINT2(WHERESTR _fmt, WHEREARG,
__VA_ARGS__)

Brs,
Markus

 

[Joel C. Salomon]

Is the following print macro "DEBUGPRINT" ok?

What do you mean by "ok"? It works, if that's what you mean.

If you're using C99, you might also want to add __function__ to the
debug output.

Given the output format, each DEBUGPRINT belongs on its own output
line -- so don't make the user include the newline.

Also note that you cannot use this version without additional
arguments; e.g.,
DEBUGPRINT("got here, no variables to display\n");
is invalid.

Here's some code I've used to accomplish much the same idea:

/* debug_print.h */
#ifndef DEBUG_PRINT_H
#define DEBUG_PRINT_H

extern void debug_print(char const *file, long line, char const *func,
char const *fmt, ...);

#define debug_print(...) \
debug_print(__FILE__, __LINE__, __func__, __VA_ARGS__)

#endif
/* end debug_print.h */

/* debug_print.c */
#include <stdio.h>
#include <stdarg.h>
#include "debug_print.h"

#undef debug_print

void
debug_print(char const *file, long line, char const *func,
char const *fmt, ...)
{
fprintf(stderr, "[%s:%ld, %s()] ", file, line, func);

va_list args;
va_start(args, fmt);
vfprintf(stderr, fmt, args);
va_end(args);

fprintf(stderr, "\n");
}

/* end debug_print.h */

(Actually, my code style include saving argv[0] in a global variable,
and I include that as well.)

Share & enjoy.

--Joel

 

[Seebs]

Hi,

Is the following print macro "DEBUGPRINT" ok?

Maybe, but... why?

// debugging macros so we can pin down message origin at a glance
#define WHERESTR "[file %s, line %d]: "

#define WHERESTR "[file " __FILE__ ", line " ...

For fun, figure out how to get the line number in there as a string so
you can use string concatenation instead of formatting.

-s

 

[Joel C. Salomon]

#define WHERESTR "[file " __FILE__ ", line " ...

For fun, figure out how to get the line number in there as a string so
you can use string concatenation instead of formatting.

Of course, the expand-and-stringify trick doesn't help with __func__.

An advantage of Seeb's suggested version is that you can define the
macro to work on both these lines:

DEBUGPRINT("foo");
DEBUGPRINT("%s", "bar");

without using the oh-so-clever PP_NARG hack, and without defining an
extra function.

You need some extra cleverness to get rid of the need for the explicit
"\n" this way, though.

--Joel

 

[Joel C. Salomon]

An advantage of Seeb's suggested version is that you can define the
macro to work on both these lines:

    DEBUGPRINT("foo");
    DEBUGPRINT("%s", "bar");

without using the oh-so-clever PP_NARG hack, and without defining an
extra function.

You need some extra cleverness to get rid of the need for the explicit
"\n" this way, though.

I nerd-sniped myself; couldn't stop till I'd solved the problem. Both
versions below my signature; as before, share & enjoy.

--Joel


#include <stdio.h>
#include <stdarg.h>


extern void debug_print(char const *file, long line, char const *func,
char const *fmt, ...)
/* __attribute__((format(printf, 4, 5))) */;

#define debug_print(...) \
debug_print(__FILE__, __LINE__, __func__, __VA_ARGS__)


#define PP_STR_(x) #x
#define PP_STR(x) PP_STR_(x)

#define PP_LOCATION __FILE__ ":" PP_STR(__LINE__) ": "

#define DEBUG_PRINT(...) do { \
fprintf(stderr, PP_LOCATION __VA_ARGS__); \
fprintf(stderr, "\n"); \
} while (0)


int
main(void)
{
debug_print("foo");
debug_print("%s", "bar");

DEBUG_PRINT("foo");
DEBUG_PRINT("%s", "bar");

return 0;
}


void
(debug_print)(char const *file, long line, char const *func,
char const *fmt, ...)
{
fprintf(stderr, "%s:%ld, %s(): ", file, line, func);

va_list args;
va_start(args, fmt);
vfprintf(stderr, fmt, args);
va_end(args);

fprintf(stderr, "\n");
}