写一个NSString类的实现

  + (id)initWithCString:(c*****t char *)nullTerminatedCString  encoding:(NSStringEncoding)encoding;**   + (id) stringWithCString: (c*****t char*)nullTerminatedCString          encoding: (NSStringEncoding)encoding   {    NSString *obj;    obj = [self allocWithZone: NSDefaultMallocZone()];    obj = [obj initWithCString: nullTerminatedCString encoding:  encoding];    return AUTORELEASE(obj);   }