__VA_ARGS__ Macro expansion

Question

I'm trying to get my macro to work like NSLog() which accepts variable arguments. Code below causes parse issues.

What is the correct way to define this?

#define TF_CHECKPOINT(f, ...) \
do { \
NSString *s = [[NSString alloc] initWithFormat:f arguments:__VA_ARGS__] autorelease]; \
[TestFlight passCheckpoint:[NSString stringWithFormat:@"%@: %@", [self class], s]]; \
} while (0)

Answer 1

You forgot the opening bracket for the autorelease message.

Moreover -[NSString initWithFormat:arguments:] expects a va_list argument, whereas __VA_ARGS__ is replaced by all the passed arguments. Here, you need to use -[NSString initWithFormat:] or +[NSString stringWithFormat:].

Finally, you may prefix __VA_ARGS__ with ##. By doing so, the preceding comma is deleted when there is no argument.

Try this:

#define TF_CHECKPOINT(f, ...) \
do { \
NSString *s = [NSString stringWithFormat:(f), ##__VA_ARGS__]; \
[TestFlight passCheckpoint:[NSString stringWithFormat:@"%@: %@", [self class], s]]; \
} while (0)