Okay, so maybe this is a total newbie question, and maybe it’s even a question better placed in a site about C, but here goes anyway: how do you allow a method to use variable numbers of arguments?

I seem to recall somebody saying on one of the lists that it was just the same as in C, but since I don’t know how to do it in C either, I have to ask anyhow.

Thanks,

– General/RobRix

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You might want to start your journey at ‘man stdarg’. Then check the archives for both Apple’s cocoa-dev list and Omni’s macosx-dev list.

– General/DaveHenderson

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Thanks very much, Dave. As it happens, I had saved an e-mail containing exactly the information I was looking for, but, being me, forgot I had saved it. Here are the contents, for any interested parties:

Daniel Staudigel wrote:

How do you declare and implement a method in obj-c (like General/NSArray’s arrayWithObjects:(id)firstObj, …)?

Declare a varargs list, e.g:

va_list args;

call the start macro:

va_start(args, firstObj);

and then call va_arg(args, typeOfWhatYouWantToRead) to get each argument in the list.

Here’s the way I did it a few weeks back:

• (General/NSString ) stringByAppendingStrings:(General/NSString *) aString, … /“This instance method returns an autoreleased string which is the result of contatenating the reciever and all of the arguments given in a nil-terminated list.”*/ { va_list strings;

  General/NSString *thisString, *result = [self stringByAppendingString:aString];

  va_start(strings, aString);

  while (thisString = va_arg(strings, id)) result = [result stringByAppendingString:thisString];

  va_end(strings); return result; }

I didn’t deal with the pathological case of someone handing me just a nil.

You might also want to have a look at the man page for varargs.

-jcr

Thanks also to John C. Randolph who wrote the above e-mail. Anyhow, that’s it.

– General/RobRix

The following version is able to handle an “empty” list (i.e. one with just a nil):

• (General/NSString ) stringByAppendingStrings:(General/NSString *) aString, … /“This instance method returns an autoreleased string which is the result of contatenating the reciever and all of the arguments given in a nil-terminated list.”*/ { va_list strings;

  General/NSMutableString *result = General/[NSMutableString stringWithString:self];

  va_start(strings, aString);

  General/NSString *thisString; for (thisString = aString; thisString; thisString = va_arg(strings, id)) [result appendString:thisString];

  va_end(strings); return result; }

See also: General/VariableLengthArgumentLists