Question

I am working on an NSData object that is 4840 bytes, and want to omit the first 20 bytes and fetch the rest. Are the substring methods substringFromIndex: / substringToIndex: applicable to NSData?

Answer 1

You are close, NSData has a method subdataWithRange:. You can make a range with the function NSMakeRange and then use that range to produce an NSData trimmed as you like.

An example:

// Create NSData
NSString* myString = @"Lorem ipsum dolor sit amet, consectetur cras amet.";
NSData*   myData   = [myString dataUsingEncoding:NSUTF8StringEncoding];
if (myData != nil && myData.length > 20) {

  // Create trimmed NSData
  NSData* newData = [myData subdataWithRange:NSMakeRange(20, myData.length - 20)];
  if (newData != nil) {

    // Test
    NSString* newString = [[NSString alloc] initWithData: newData 
                                                encoding: NSUTF8StringEncoding];
    NSLog(@"%@", newString);
    // -> "t amet, consectetur cras amet."
  }
}