Re: variadic macros and and empty replacement for __VA_ARGS__

On 2006-03-27, John Devereux <jdREMOVE@xxxxxxxxxxxxxxxxxx> wrote:
Urs Thuermann <urs@xxxxxxxxxxxxxxxxx> writes:

I want to write a macro that produces debug output and has a variable
number of arguments, so that I can use like this:

int i;
char *s;

DBG("simple message\n");
DBG("message with an int argument, value is %d\n", i);
DBG("two arguments: int %d, strings %s\n", i, s);

The output should be a fixed prefix, say "DEBUG ", followed by the
function name the macros is used in, and then by the string passed to
the macro, including further arguments.

The best solution I have found so far, is

#define DBG(fmt, ...) printf("DEBUG %s:" fmt, __func__, __VA_ARGS__)

<SNIP>
Is there a better way to write the DBG() macro to avoid this?


There was a related thread a couple of weeks ago:

<http://groups.google.co.uk/group/comp.lang.c/browse_frm/thread/ac0bda529a91d754/949239c624c9fe71?lnk=st&q=logging+group%3Acomp.lang.c&rnum=3&hl=en#949239c624c9fe71>

This basically used a *function* instead of a macro. The logging
function accepts variadic arguments, and these can then be modified
and passed on to a varargs form of printf (e.g. vfprintf).


One little thing you might consider at an early stage : have an
importance or category enum as the first/second parameter : very
useful for filtering/enabling/disabling runtime logging for different
subsets in a non trivial system. You might even use the function name
and have settings to enable/disable logging for the particular function.
.

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