Question

I wanted to track some options via bitmask’ing them, and borrowed bitmask values from this answer, yet they not seem to work together.

#include <iostream>

#define OP1 0x00003FFFUL
#define OP2 0x00007FFFUL
#define OP3 0x0000FFFFUL

int main() {
        unsigned long params = 0; // .
        params |= OP3;
        if ( (params & OP1) == OP1)
                std::cout << "Whoa. Lame masking\n";
}

Is it a type problem, or this method can’t be used for holding more than 1 option at a time (both OP1, OP2 and OP3 are wanted to stay in same params)?

Answer 1

For options you should use other masks, ones that are not overlapped, such as:

   #define OP1 0x000000FUL
   #define OP2 0x00000F0UL
   #define OP3 0x0000F00UL

or (in this case you’ll be able to store as many options as available bits):

   #define OP1 0x0000001UL
   #define OP2 0x0000002UL
   #define OP3 0x0000004UL
   //ETC...

Your masks will never work properly because if OP3 is set then OP1 and OP2 will be contained (the same goes if you use OP2, then OP1 will be implied):

     FFFF = 1111111111111111
  &  3FFF = 0011111111111111
     -----------------------
     3FFF = 0011111111111111

The masks in the example you pasted were intended to extrapolate the last bits of an UL.