I have been trying to implement a function macro in C that prepends "DEBUG: ", to the argument, and passes its arguments to printf:
#define DBG(format, ...) printf("DEBUG: " #format "\n", __VA_ARGS__)
This gives me this error in gcc:
src/include/debug.h:4:70: error: expected expression before ‘)’ token
#define DBG(format, ...) printf("DEBUG: " #format "\n", __VA_ARGS__)
^
Supposedly, it should stringise format, and pass its variable arguments to printf, but so far I can't get past this error.
EDIT
After giving up on stringising arguments, and double-hashing (##
) __VA_ARGS__
I now have this error:
src/lib/cmdlineutils.c: In function ‘version’:
src/lib/cmdlineutils.c:56:17: warning: ISO C99 requires rest arguments to be used [enabled by default]
DBG("version()");
Should I be placing a comma after the argument?
DBG("version()",); // ?
For reference, DBG() now looks like this:
#define DBG(format, ...) printf("DEBUG: " format "\n", ##__VA_ARGS__)
This happens unless there's at least one variable argument. You can try this GNU extension to fix it:
#define DBG(format, ...) printf("DEBUG: " #format "\n", ##__VA_ARGS__)
^^
As explained in the GNU doc:
[if] the variable argument is left out when the macro is used, then the comma before the ‘##’ will be deleted.