Parsing NSData by byte count

Question

I have NSData and i would like to parse it by bytes. Here is an example. data is <8283010c ec4f483f 0d00000c 0c0f2840 >

I would like to pass 8 bytes to each object i create (8283010c ec4f483f for first object,0d00000c 0c0f2840 for the second) , and then parse those each bytes like this.

  //  First byte > Action = 82
  //  2nd and 3rd byte > Status = 83 01
  //  4,5,6,7 byte > Time = 0c ec 4f48
  //  8 byte > Number = 3f

How could i parse NSData to such structure, what types should i use for my variables (Action)?

unsigned char aBuffer[8];
[data getBytes:aBuffer length:8];

Tried to do a little test in such way, but NSLog prints aBuffer with strange symbols, instead of byte values.

Well, what do you mean by "parsing"? In this context, it doesn't quite make sense. Why don't you just copy 8 bytes from `[data bytes] + offset * 8` anyway? — , Dec 21 '12 at 13:30
What encoding does the data use? It may be returning 4 unichar characters instead of 8 ASCII characters.You should also tell us the definition of the structure, the one you provided isn't clear. — Ramy Al Zuhouri, Dec 21 '12 at 13:34
There is no encoding for data. It's raw data. It would be great if i could convert this data to like NSString somehow. H2CO3 could you write a simple example on how to do this, or point me where could i learn this. Because currently this is a dark forest to me with no light. — Datenshi, Dec 21 '12 at 13:36
@Datenshi Have you ever used `printf()`? If not, have you tried reading and understanding the documentation of `NSData`? I don't think so... — , Dec 21 '12 at 13:37
Yes I'v tried both, your comment makes me feel kinda stupid. Your answer did help me, and that was exactly what i was asking for, thank you for your time. And sorry for not being smart enough to grasp everything without help :) — Datenshi, Dec 21 '12 at 13:42

score 3 · Accepted Answer · answered Dec 21 '12 at 13:36

NSLog prints aBuffer with strange symbols, instead of byte values.

Because those are the actual bytes NSData contains, and not their hexadecimal representation. If you want a hexadecimal representation, you have to format the bytes accordingly:

NSMutableString *hexRepr = [NSMutableString string];
for (int i = 0; i < 8; i++) {
    [hexRepr appendFormat:@"%02x", ((uint8_t *)[data bytes])[offset * 8 + i]];
}

score 0 · Answer 2 · edited Jun 20 '20 at 09:12

0

As a follow up on @H2CO3's answer,

According to NSData docs, [data description] returns hexadecimal representation. Wouldn't that be easier?

UPDATE: Found why [data description] shouldn't be used: https://stackoverflow.com/a/9084784/58505

edited Jun 20 '20 at 09:12

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answered Mar 26 '13 at 21:23

pixelfreak

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Parsing NSData by byte count

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