method with 2 return values

Question

I want to call a method which returns two values

basically lets say my method is like the below (want to return 2 values)

NSString* myfunc
{
   NSString          


        

Answer 1

You have a few options:

• NSArray: Just return an array. Pretty simple.
• Pointers: Pass in two pointers, and write to them instead of returning anything. Make sure to check for NULL!
• Structure: Create a struct that has two fields, one for each thing you want to return, and return one of that struct.
• Object: Same a structure, but create a full NSObject subclass.
• NSDictionary: Similar to NSArray, but removes the need to use magic ordering of the values.

Answer 2

As you can only return one value/object, maybe wrap them up in an array:

-(NSArray*) arrayFromMyFunc
{
   NSString *myString = @"MYDATA";
   NSString *myString2 = @"MYDATA2";
   return [NSArray arrayWithObjects:myString,myString2,nil];
}

You can then use it like this:

NSArray *arr = [self arrayFromMyFunc];

NSString *value1 = [arr objectAtIndex:0];
NSString *value2 = [arr objectAtIndex:1];

You could pass results back by reference, but this is easy to get wrong (syntactically, semantically, and from memory management point of view).

Edit One more thing: Make sure that you really need two return values. If they are quite independent, two separate function are often the better choice - better reusabilty and mentainable. Just in case you are making this as a matter of premature optimization. :-)

Answer 3

Wrap the two strings in an NSArray:

- (NSArray*)myFunc
{
   NSString *myString = @"MYDATA";
   NSString *myString2 = @"MYDATA2";
   return [NSArray arrayWithObjects:myString, myString2, nil];
}

NSArray *theArray = [self myFunc]
NSString *value1 = [theArray objectAtIndex:0];
NSString *value2 = [theArray] objectAtIndex:1];

Answer 4

You can only return 1 value. That value can be a struct or an object or a simple type. If you return a struct or object it can contain multiple values.

The other way to return multiple values is with out parameters. Pass by reference or pointer in C.

Here is a code snippet showing how you could return a struct containing two NSStrings:

typedef struct {
    NSString* str1;
    NSString* str2;
} TwoStrings;

TwoStrings myfunc(void) {
    TwoStrings result;
    result.str1 = @"data";
    result.str2 = @"more";
    return result;
}

And call it like this:

TwoStrings twoStrs = myfunc();
NSLog(@"str1 = %@, str2 = %@", twoStrs.str1, twoStrs.str2);

You need to be careful with memory management when returning pointers even if they are wrapped inside a struct. In Objective-C the convention is that functions return autoreleased objects (unless the method name starts with create/new/alloc/copy).

Answer 5

You can only directly return one value from a function. But there is a way of doing it.

-(void) myfuncWithVal1:(NSString**)val1 andVal2:(NSString**)val2
{
  *val1 = @"MYDATA";
  *val2 = @"MYDATA2";
}

Then to call it outside the method you'd use:

NSString* a;
NSString* b;

[self myfuncWithVal1:&a andVal2:&b];

Answer 6

void myfunc(NSString **string1, NSString **string2)
{
    *string1 = @"MYDATA";
    *string2 = @"MYDATA2";
}

...

NSString *value1, *value2;
myfunc(&value1, &value2);

Remember that you need to pass a pointer to a pointer when working with strings and other objects.