Iterate through variable number of arguments in function without passing nil - objective-c

Question

I, like many, constantly have to look up date codes for date formatter. I decided to make a file that will make it easier for me to remember them all. I include a function for readability that I declare like this:
NSString * dateFormatString(NSString * string1, ...) {
// Parse out Args
va_list args;
va_start(args,string1);
// Set up our Format String
NSMutableString * formatString = [NSMutableString string];
// Build Format string
for (NSString * arg = string1; arg != nil; arg = va_arg(args, NSString*)) {
[formatString appendString:arg];
}
va_end(args);
return formatString;
}
So, I can then program my NSDateFormatter like this:
dateFormatter.dateFormatString = dateFormatString(DKDayOfWeekFull, #", ", DKMonthNameFull, #" ", DKDayOfMonthComplete, nil);
You could do achieve pretty much the same thing by declaring:
[NSString stringWithFormat:#"%#, %# %#", DKDayOfWeekFull, DKMonthNameFull, DKDayOfMonthComplete];
However, if you're describing a date with more variables like "Sat, Jan 14 2006 at 7:52 AM" it would have to be:
NSString * dateFormatterString = [NSString stringWithFormat:#"%#, %# %# %# 'at' %#:%# %#", DKDayOfWeekAbbreviated, DKMonthNameAbbreviated, DKDayOfMonthComplete, DKYearComplete, DKHour12hrComplete, DKMinutes2Digits, DKAmPm];
Which I personally think is a bit more readable like this:
NSString * dateFormatterString = dateFormatString(DKDayOfWeekAbbreviated, #", ", DKMonthNameAbbreviated, #" ", DKDayOfMonthComplete, #" ", DKYearComplete, #"'at' ", DKHour12hrComplete, #":", DKMinutes2Digits, #" ", DKAmPm, nil);
Question
I would prefer a way to iterate through the variables without having to pass nil into the function. Is there another way to iterate through a variable argument list, other than:
for (NSString * arg = string1; arg != nil; arg = va_arg(args, NSString*)) {
[formatString appendString:arg];
}

Answer 1

I assume you meant to say dateFormatter.dateFormat = ..., since NSDateFormatter has no dateFormatString property.
I assume DKDayOfWeekAbbreviated is a string constant defined as #"E", and DKDayOfWeekFull is #"EEEE", and so on, based on UTS #35.
If that is so, here's a different approach. Define your constants like this:
#define DKDayOfWeekAbbreviated #"E"
#define DKDayOfWeekFull #"EEEE"
#define DKMonthNameFull #"MMMM"
#define DKDayOfMonthComplete #"dd"
Then use compile-time string concatenation to build your strings. The compiler merges two adjacent string constants. For example, "hello " "world" becomes "hello world", and #"hello " #"world" becomes #"hello world". In fact, you can omit the second and later # characters, so #"hello " "world" becomes #"hello world".
Thus:
dateFormatter.dateFormat = DKDayOfWeekFull ", " DKMonthNameFull " " DKDayOfMonthComplete;
You don't need a helper function or varargs.

Answer 2

The only way to support variable arguments using the standard C syntax is to do what you are doing.
But you have another option - use an NSArray.
Your function becomes:
NSString * dateFormatString(NSArray *strings) {
// Set up our Format String
NSMutableString * formatString = [NSMutableString string];
// Build Format string
for (NSString * arg in strings) {
[formatString appendString:arg];
}
return formatString;
}
or simply do:
NSString * dateFormatString(NSArray *strings) {
return [strings componentsJoinedByString:#""];
}
And you call it like this:
dateFormatter.dateFormatString = dateFormatString(#[ DKDayOfWeekFull, #", ", DKMonthNameFull, #" ", DKDayOfMonthComplete ]);
No need for nil using the modern NSArray syntax.