Question

This is for practise. I try to build something similar to NSLog. Currently I have this:

#define LogThis(info) \
    [[MyLogger sharedLogger] logThis:info];\


- (void)logThis:(NSString*)info {
    fprintf(stderr, [[NSString stringWithFormat:@"  %@\n", info] cString]);
}

Currently all I can do is pass a simple @"string" to it, but no formats and arguments like I could with NSLog. The main advantage here is that I get rid of all this overhead which NSLog produces. For learning purpose I’d like to know how I can get multiple arguments to make something similar to NSLog, so that I could call:

LogThis(@"method foo received input value %d", inputValue)

Is this possible?

Answer 1

Here’s how you define variadic macros in gcc’s cpp:

#define LogThis(format, ...) \
    do { printf(format, ## __VA_ARGS__); } while(0)