iPhone - Creating variadic functions in objective c issue - iphone

Question

I referred this SO Answer for creating variadic function in objective C.
I tested your code by passing arguments like below:
[self logMessage:#"string: %#\n number: %#\n image: %#",
#"asdf",
[NSNumber numberWithInt:23],
[UIImage imageNamed:#"local.png"]];
and edited the code with NSLog();
- (void)logMessage:(NSString *)format, ... {
va_list args;
va_start(args, format);
id arg = nil;
int i = 1;
NSLogv(format, args);
while ((arg = va_arg(args,NSString *))) {
NSLog(#"val: %d", i++);
/// Do your thing with arg here
//NSString *name = NSStringFromClass([arg class]);
//NSLog(#"string: %#", name);
}
va_end(args);
}
But the output as follows:
2012-09-28 19:34:45.271 SIMO[2384:c07] string: asdf
number: 23
image: <UIImage: 0x8151f80>
2012-09-28 19:34:45.273 SIMO[2384:c07] val: 1
2012-09-28 19:34:45.273 SIMO[2384:c07] val: 2
2012-09-28 19:34:45.274 SIMO[2384:c07] val: 3
2012-09-28 19:34:45.274 SIMO[2384:c07] val: 4
2012-09-28 19:34:45.274 SIMO[2384:c07] val: 5
2012-09-28 19:34:45.275 SIMO[2384:c07] val: 6
2012-09-28 19:34:45.275 SIMO[2384:c07] val: 7
2012-09-28 19:34:45.276 SIMO[2384:c07] val: 8
This tells that the argument is 8, but I passed only 3 (NSString, NSNumber, UIImage)
I can't get the concept.. Could you clarify me
Could anyone clarify this

Answer 1

va_arg doesn't really know when the argument list ends. The approach you're using expects the argument list to be terminated by nil, like +[NSArray arrayWithObjects:].
So either change your invocation to add nil at the end of the argument list, or find some other way of knowing when the arguments are over (e.g. for a printf clone, you might know the number of format arguments from the format string itself).