Preprocessor macro question

Preprocessor macro question

[Joe MacDonald]

Hi folks,

I looked around in the archives but couldn't find a conclusive answer to
my question.  I have the following macro defined:

#ifdef _J_DEBUG_
#define debugDump(format, ...) \
   fprintf(stderr, "%s:%d> ", __FILE__, __LINE__); \
   fprintf(stderr, format, ##__VA_ARGS__ )
#else
#define debugDump(format, ...)
#endif

And I'm defining _J_DEBUG_ at compile time.  Now in a file called cmd.c
I have the following:

17   debugDump("not a command node");
18   !xmlnode->name ?
19      debugDump("xmlnode->name == NULL\n") :
20      debugDump("xmlnode->name == \"%s\"\n", "foo") ;

And when I compile I see this:

cmd.c:20:54: warning: pasting would not give a valid preprocessing token
cmd.c:25:67: warning: pasting would not give a valid preprocessing token
cmd.c: In function `addCommand':
cmd.c:19: parse error before `;'
cmd.c:19: parse error before `:'
make: *** [cmd-d] Error 1

So here's my question.  Have I done something particularly wrong, or is
this related to a bug back in September 2000 discussed in the thread at
http://gcc.gnu.org/ml/gcc/2000-09/msg00138.html by Zack Weinberg among
others?  I suspect it is since I'm currently using gcc 2.96 (from a Red
Hat 7.0 install through no fault of my own. ;-) ) but before I start
asking for folks on the team to upgrade the compiler, I'd like some
advice.

Thanks,
-Joe.

-- 
Joe MacDonald
:wq

Re: Preprocessor macro question

[John Love-Jensen]

Hi Joe,

That's not a well formed macro.  Do this instead...

#define debugDump(x) \
    printf("%s:%d> ", __FILE__, __LINE__); \
    printf x

void Foo(const char* inName) {
    debugDump(("%s %s %s\n", "Hi", "there", inName));
}

Note:  If you want to do stderr, you'll need a stub routine which uses
vfprintf coded to spit out to stderr.

Also, you need the double-parens to contain the parms.  Icky.

But there's an even better C++ way anyway.

// Caution:  macro magery.
#define debugDump(x) \
    cerr << __FILE__ << ":" << __LINE__ << "> " << x << endl;

void Foo(const string& inName) {
    debugDump("Hi" << " " << "there" << " " << inName);
}

And if you have some sort of log levels, you can add that into the
macro-magic.  (Note:  macro-magic is usually considered bad, this is one of
the few cases where I find it acceptable in C++.  I wish invoking a macro
REQUIRED an octalthorpe ('#') character on the end of a macro name.  *sigh*)

namespace Log {
enum Level_t { kEmergency, kAlert, kCritical, kError, kWarning, kNotice,
kInfo, kDebug };
Level_t gLevel = kError;
} // namespace Log

// Caution:  macro magery.
#define debugDump(log, x) \
    if(log < Log::gLevel) { \
        std::ostringstream debugDump_theOutput; \
        debugDump_theOutput << __FILE__ << ":" << __LINE__ << "> " << x <<
std::endl; \
        gLoggingFacility.logMessage(debugDump_theOutput.str()); \
    }

void Foo(const string& inName) {
    debugDump(kLogInfo, "Hi" << " " << "there" << " " << inName);
}

Happy debugging!

--Eljay