Converting NSData to int

Question

I've an NSData object, the length is 4 bytes .These four bytes i'm extracting from another NSData object using ,

fourByteData=[completeData subdataWithRange:NSMakeRange(0, 16)];

My first question is, will the above statement provide me the first four bytes of complete data.

If Yes, then how to convert all these bytes to an equivalent int.

Answer 1

Is 268566528 the value you expect or perhaps you expect 528? If the correct value is 528 then the byte order is big-endian but the cpu is little-endian, the bytes need to be reversed.

So, if the correct value should be 528 then:

NSData *data4 = [completeData subdataWithRange:NSMakeRange(0, 4)];
int value = CFSwapInt32BigToHost(*(int*)([data4 bytes]));

Also note that network standard order is big-endian.

Answer 2

That statement would give you the first 16 bytes of data, not 4. To get the first 4 bytes you need to modify your statement to:

fourByteData = [completeData subdataWithRange:NSMakeRange(0, 4)];

To read the data from the NSData Object to an integer you could do something like:

int theInteger;
[completeData getBytes:&theInteger length:sizeof(theInteger)];

You do not need to get the first 4 bytes if you are just converting it to an integer. You can do this directly from the two lines above and your completeData receiver