Question

I have created a method that accept variadic arguments like

- (NSDictionary *) getImagePixelsAtLocation: (int) locations,...NS_REQUIRES_NIL_TERMINATION

but when I send message to this class method, the value of locations variable in called method is 0 (it does not matter how many arguments I pass).

The method receives scalar data types. My question is: Can we pass scalar variable to a method as variadic arguments? If yes, what am I doing wrong?

The method definition is:

- (NSDictionary *) getImagePixelsAtLocation: (int) pixel1,...
{
    NSMutableDictionary *dict = [NSMutableDictionary dictionary];
    va_list args;
    va_start(args, pixel1);

    //processing logic


    va_end(args);
} 

This is how I am sending message:

[HSImageProcessing getImagePixelsAtLocation:1,2,nil];

Answer 1

Actually, there is one glaringly obvious flaw in your code there: when a variadic function is nil-terminated, the accepted type must be an object. You cannot compare an int to nil or NULL, or [NSNull null], which defeats the purpose of nil-termination, and effectively defeats all chances of iteration using the standard for and for-in loops. In addition, NSDictionary isn’t too happy about storing non-object types, and will happily make the compiler complain. I’ve rewritten it to accept NSNumber*, and output a dictionary of numbers.

- (NSDictionary*) getImagePixelsAtLocation: (NSNumber*) pixel1,...
{
    NSMutableDictionary *dict = [NSMutableDictionary dictionary];
    va_list args;
    va_start(args, pixel1);

    //processing logic
    for (NSNumber* arg = pixel1; arg != nil; arg = va_arg(args, NSNumber*)) {
        [dict setObject:arg forKey:[NSString stringWithFormat:@"%i", [arg intValue]]];
    }

    va_end(args);
    return dict;
}

All it takes is a little bit of extra code on your part to get that very same call working as well:

[self getImagePixelsAtLocation:[NSNumber numberWithInt:1],[NSNumber numberWithInt:2],nil];