Question

I haven’t found any get equivalent to appendBytes. If I’ve understood getBytes correctly, that method always returns bytes from the start of the buffer. It will not increment.

What’s the reason for this?

Answer 1

There are several methods that give you access to some part of the data in a NSData object. For example, you can use -getBytes:range: to copy the data specified by a NSRange into a buffer. Or you can use -subdataWithRange: to get a NSData that contains just a portion of another.

If you want to read sequentially through the contents of a NSData object, you can create a NSInputStream and initialize it with your NSData, and then read from the stream using -getBuffer:length: or -read:maxLength:.

NSInputStream *stream = [[NSInputStream alloc] initWithData:myData];
[stream open];
while ([stream read:&buffer maxLength:bufferLength] > 0) {
    // do something with buffer
}

Note: you obviously don’t need the while loop in the code above if you’re not doing the same thing to each chunk of data that you read — I just included it because it’s a common way to read data.