How To Test PHP Bitwise Function Input Parameters

Question

Sometimes in programming they allow one to chain parameters in a single function input variable like the second input variable below:

define('FLAGA',40);
define('FLAGB',10);
define('FLAGC',3);
function foo($sFile, $vFlags) {
  // do something
}
foo('test.txt',FLAGA | FLAGB | FLAGC);

PHP calls this single pipe character (|) the Bitwise OR operator. How do I now add something inside foo() to test $vFlags to see which flags were set?

Answer 1

I think you'll find that flags like this are normally defined as powers of 2, e.g.:

define('FLAGA',1);
define('FLAGB',2);
define('FLAGC',4); /* then 8, 16, 32, etc... */

As you rightly stated, these can be combined by using a bitwise OR operator:

foo('test.txt',FLAGA | FLAGB | FLAGC);

To test these flags inside your function, you need to use a bitwise AND operator as follows:

function foo($sFile, $vFlags) {
  if ($vFlags & FLAGA) {
    // FLAGA was set
  }
  if ($vFlags & FLAGB) {
    // FLAGB was set
  }
  //// etc...
}