Question

I need to use a method that returns several strings, different ones, according to a value.
My code looks like:

- (void) returnStringsAccordingToSet:(NSString *)string1: (NSString *)string2: (NSInteger)setNo {
    switch (setNo){
        case 1:
            if (generalStringSettings){
                string1 = @"The first string";
                string2 = @"The second string";
            } else {
                string1 = @"The first other string";
                string2 = @"The second other string";
            }
            break;
        case 2:
             ...
             break;
        case 3:
             ...
             break;
    }
}


I call that method with:

NSString *firstString = [[NSString alloc]init];
NSString *secondString = [[NSString alloc]init];
NSUInteger set  = 1;

[self getStringsAccordingToSet: firstString: secondString: set];

I can’t get it to work! All I get is empty strings. I’ve got a feeling that the call for the strings is somewhat wrong. Please help.

Answer 1

You could do this by filling a NSArray, but just to show how C works I’ll show the error that you made.
string1 and string2 are just pointers, so you can pass either mutable or immutable strings as arguments.But the original pointer never gets modified, for example:

NSString* string1=@"Hello";  // Let's suppose string1 is on the 0x8000 address
                             // And points to the 0x9000 address
NSString* string2=@"How are you?";  // string2: 0x1000 , pointing to 0x2000
[self returnStringsAccordingToSet: string1: string1 string2: string2];

Then when you call a method a copy is made for every pointer that you pass to the method:

- (void) returnStringsAccordingToSet:(NSString *)string1: (NSString *)string2: (NSInteger)setNo {
// string1 and string2 both point on the same address, but they are other pointers
// for example string1 is on 0x7000 and string2 on 0x7400, pointing to 0x9000
// and 0x2000
    switch (setNo){
        case 1:
            if (generalStringSettings){
                string1 = @"The first string";  // You just create another instance
                string2 = @"The second string"; // of the string, but the original
                // pointers aren't affected
            } else {
                string1 = @"The first other string";
                string2 = @"The second other string";
            }
            break;
        case 2:
             ...
             break;
        case 3:
             ...
             break;
    }
}

The solutions:

1. Pass a NSMutableString as argument and instead of assigning them, just modify the contents;
2. Pass a pointer to pointer;
3. Return a NSArray containing the new strings.