How to get an NSString from a non-terminated array of unicode chars (length is known)

FROM : Stuart Malin
DATE : Tue Mar 04 08:00:59 2008

My problem is that I receive a function call from a C library that 
gives me a wchar_t array and its length. The unicode array is _not_ 
terminated.

The library defines an XML_Char type, so my code below refers to 
that, but XML_Char is wchar_t (which, I believe is UTF8 on a Mac).

I'm very weak with C, so please forgive my perhaps naive attempts here.

I tried this approach:

   NSMutableData *data = [NSMutableData dataWithBytes:(void *)s 
length:len];  //as supplied, s is: (const XML_Char *), and len is its 
length
   //append a NULL unicode char
   XML_Char nullChar = 0;
   XML_Char *nullCharPtr = &nullChar;
   int nullCharLen = sizeof nullChar;
   [data appendBytes:nullCharPtr length:nullCharLen];
   NSString *str = [NSString stringWithUTF8String:(const char*)data];

The idea being to append a NULL to the non-terminated library 
supplied wchar_t array, and then convert given its encoding.
But that gives me nil (even though my test data is plain old ASCII 
caracters, so all the XML_Chars are single bytes).

So, in experimenting, I tried this:

   NSMutableString *ms = [NSMutableString stringWithCapacity:len];
   int i;
   for (i = 0; i<len; i++) {
       [ms appendFormat:@"%C", s[i]];
   }
   NSLog(@"string is: %@", ms);

That works, but obviously is quite inefficient.

There must be a sensible way to do this?

Many thanks in advance for whatever help someone(s) can provide.
--Stuart