C & PHP: Storing settings in an integer using bitwise operators?

Question

I\'m not familiar with bitwise operators, but I have seem them used to store simple settings before.

I need to pass several on/off options to a function, and I\'d li

Answer 1

quote "the idea is not good, really. you would better pass few boolean. if you want use bitwise then

function someFunc($options)
{

   if ($options & 1 != 0)
      //then option 1 enabled
   if ($options & (1 << 1) != 0)
      //then option 2 enabled      
   if ($options & (1 << 2) != 0)
      //then option 3 enabled      
}

"

What you have done would be okay if you were checking for a single value, although not optimal, so checking that a bit is enabled, but lets say we wanted to be able to match any, or exact we could have the following methods

function matchExact($in, $match) { // meets your criterion, as would a switch, case, but ultimately not suited for use with flags
    return $in === $match;
}

function matchAny($in, $match) { // meets original criterion with more lexical name however it returns true if any of the flags are true
    return $in |= $match;
}

if you then wanted to expand upon this by having specific actions only happening if bit x,y,z was enabled then you could use the following

function matchHas($in, $match) { // more bitwise than === as allows you to conditionally branch upon specific bits being set
    return $in &= $match;
}

I also think if you are doing what was done in the above quote, flags may not be the best idea, exact values might be better, which does have the benefit of allowing more discreet actions. (0-255) for 8-bit over 8 distinct flags

The whole reason flags work so well is because in base 2 "8" does not contain "4", and "2" does not contain "1".

 ________________________
 |8|4|2|1|Base 10 Value |
 ------------------------
 |1|1|1|1|15            |
 |1|1|1|0|14            |
 |1|1|0|1|13            |
 |1|1|0|0|12            |
 |1|0|1|1|11            |
 |1|0|1|0|10            |
 |1|0|0|1|9             |
 |1|0|0|0|8             |
 |0|1|1|1|7             |
 |0|1|1|0|6             |
 |0|1|0|1|5             |
 |0|1|0|0|4             |
 |0|0|1|1|3             |
 |0|0|1|0|2             |
 |0|0|0|1|1             |
 |0|0|0|0|0             |
 ------------------------