Question

If have an array of char’s pulled out of an NSData object with getBytes:range:

I want to test if a particular bit is set. I would assume I would do it with a bitwise AND but it doesn’t seem to be working for me.

I have the following:

unsigned char firstBytes[3];
[data getBytes:&firstBytes range:range];

int bitIsSet = firstBytes[0] & 00100000;

if (bitIsSet) {
  // Do Something
}

The value of firstBytes[0] is 48 (or ‘0’ as an ASCII character). However bitIsSet always seems to be 0. I would imagine I am just doing something silly here, I am new to working on a bit level so maybe my logic is wrong.

Answer 1

If you put a 0 before a number you are saying it’s expressed in octal representation.
00100000 actually means 32768 in decimal representation, 10000000 00000000 in binary representation.

Try

int bitIsSet = firstBytes[0] & 32;

or

int bitIsSet = firstBytes[0] & 0x20;