I must be missing something... (Categories)

Reading through the Objective C docs from Apple, I'm seeing this 
neat-sounding thing called "categories", whereby one can extend existing 
objects.

So, since I'm working with a wad of raw data (held by an NSMutableData 
object) that needs to do many searches for "magic strings" in the wad to 
locate the bits of data that it's actually interested in, I figured 
"This is a good place to do some extending".

I came up with the following. Apologies for blown line-wrapping - pasted 
directly from XCode, complete with my attempts at figuring out what's 
going wrong via printf(). And yes, I'm aware it's crude, clunky, and has 
its own built-in problem - as noted in the comment. If you'd be so kind 
as to ignore those details and concentrate on helping me figure out why 
it isn't working *AT ALL* (not even incorrectly...) I'd appreciate it:

-=-=-=- begin .h file
#im****t <Cocoa/Cocoa.h>

@[EMAIL PROTECTED]
 NSMutableData (Search)
- (unsigned)findNSString:(NSString *)targetString 
startingAt:(unsigned)Start;
@[EMAIL PROTECTED]
 end .h file

-=-=-=-- begin .m file
#im****t "NSMutableDataSearch.h"

// Extending NSMutableData by adding a crude findString:startingAt 
routine for NSMutableData objects.
// Takes an NSString (the target) and a starting location (offset from 
the start of the NSMutableData buffer). 
// Returns 0 = Not found (or found at location 0! Small problem here!) 
or non-zero for found.
// Restrictions: Best bet is to avoid sending this message to an 
instance unless it's known that the target data WILL NOT be found at 
offset 0...

@[EMAIL PROTECTED]
 NSMutableData (Search)

- (unsigned)findNSString:(NSString *)targetString 
startingAt:(unsigned)Start
{
   unsigned Max;
   unsigned Index;
   NSString *TempString;
   char TempCString[255];

   printf("Entering findNSString\n");
   Max = [self length];
   Index = 0;
   
   printf("findNSString: TargetString = '%s', Max = %d\n", [targetString 
getCString:&TempCString[0]], Max);
   for (Index=Start;Index < Max;Index++)
    {
      TempString = [NSString stringWithCharacters:([self 
mutableBytes]+Index) length:[targetString length]];
      printf("Checking against '%s'...\n", [TempString 
getCString:&TempCString[0]]);
      if ([targetString isEqualTo:TempString])
       {
         printf("Got a match in findNSString!\n");
         break;
       }
      else
       {
         printf("No match in findNSString\n");
       }
    }
   if (Index < Max)
      return Index;
   else
      return 0;
}

@[EMAIL PROTECTED]
 end .m file


Looks OK "on paper", but doesn't operate *AT ALL* in reality - When 
called, it does *ABSOLUTELY NOTHING*. It's as if it doesn't exist at all 
- No printf output from any of the diagnostics, and the returned value 
is zero every time. Trying to "step into" it in the debugger does 
zip-ola - It's as if it's a null statement.

So it would appear that I'm doing something wrong, misunderstanding the 
use of categories, or some of both. 

Hints? Clarifications? Assistance?

-- 
Don Bruder - dakidd@[EMAIL PROTECTED]
 - If your "From:" address isn't on my
whitelist,
or the subject of the message doesn't contain the exact text
"PopperAndShadow"
somewhere, any message sent to this address will go in the garbage without
my
ever knowing it arrived. Sorry... <http://www.sonic.net/~dakidd>
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