CODEWITHSUNDEEP
c
user4284784
user4284784

Reputation:

C macro with special variable arguments

I always write below code for debug purpose:

printf("%s:%d this is a string %s int %d",__FUNCTION__,__LINE__,strval,intval);

Now since the first part (FUNCTION,LINE) is always used, so I wish to create a macro to do it and just append other debug strings.

Maybe looks like:

#define MYPRINT(args...) printf("%s:%d",__FUNCTION__,__LINE__);printf(##args)

But I wish to use one statement rather than two as above! Is it possible?

Clarify not duplicate of this one

This is different because I wish to add some new field into print command. actually answers here is great, thanks for all's help!

Upvotes: 7

Views: 314

Answers (3)

Quentin
Quentin

Reputation: 63124

How about this :

#include <stdio.h>

#define MYPRINT(fmt, ...) \
    printf("[%s]:%d - " fmt "\n", __FUNCTION__, __LINE__, __VA_ARGS__)

int main() {
    char const *s = "My string";
    int i = 42;
    MYPRINT("%s, %d", s, i);
}

Outputs :

[main]:8 - My string, 42

Upvotes: 1

jxh
jxh

Reputation: 70402

If you want a single call to printf(), your MYPRINT needs to be aware of a format string. You can try something like this, so long as the format string is a literal:

#define MYPRINT(FMT, ...) printf("%s:%d " FMT, __FUNCTION__, __LINE__, ##__VA_ARGS__)

The ## is a GCC (and perhaps others) compiler extension that swallows the comma in the case __VA_ARGS__ is actually empty. If your compiler does not support it, leave it off.

Upvotes: 5

ouah
ouah

Reputation: 145829

You can use a variadic macro and use , to have one statement:

#define MYPRINT(...) (printf("%s:%d",__FUNCTION__,__LINE__), printf(__VA_ARGS__))

Upvotes: 4

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