Terminating the app due to uncaught exception in Objective-C for iPhone app

Question

Hello, i've written a for loop in Objective-C, This is how my code looks like

NSString *string = [NSString stringWithContentsOfFile=@"/Users/Home/myFile.doc"];
NSString *seperator=@"\n";
NSArray *mainarray = [string componentsSeparatedByString:seperator];
// Since i want to parse each element of mainarray
for(NSString *s in mainarray)
{
  //again parising the string using a new separator
    NSString newseparator = @"=";
    NSArray *subarray = [s componentsSeparatedByString : newseparator];

  //Copying the elements of array into key and object string variables

    NSString *key = [subarray objectAtIndex:0];
    NSLog(@"%@",key);
    NSString *class_name= [subarray objectAtIndex:1];
    NSLog(@"%@",class_name);

   // create an instance for the class_name
      //dont knw how it ll take the value from file and ???  

 //Putting the key and objects values into hashtable 
    NSMutableDictionary = [NSDictionary dictinaryWithObject:class_name forKey:key];
}

Whenever i execute this code this crashes my program saying as, Terminating the app due to uncaught exception NSRangeException

How to know the range of array and how to specify the terminating condition in the for loop???and plz let me knw how to handle this exception???

Answer 1

I'm surprised that code even compiles. If I remember correctly, it can't compile unless you have gone to great lengths to turn off a whole bunch of compiler warnings.

NSString newseparator = @";";

That should give an error write there in that you don't have the *.

NSString *key = [subarray objectAtIndex[0]];
NSString *object = [subarray objectAtIndex[1]];

Neither of these lines of code make any sense.

It would appear that you haven't posted the actual code?

---

Now, getting back to the exception. A range exception will be tossed if you try to access an item at an index that is outside of the range of indexes available in the array. Thus, if componentsSeparatedByString: returned an array of 0 or 1 elements, then [subarray objectAtIndex: 1]; will cause a range exception to be raised.

What you don't want to do is to try and handle the exception using an @catch block. In Cocoa (and iPhone development), exceptions are treated as non-recoverable errors.

So, instead, use the -count method on NSArray to verify that the array actually contains the # of elements you were expecting. Since you are writing a casual parser, this is probably a good idea as a minimal check of input validity.