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

You sure can do it in PHP.

Let's say you have four booleans you want to store in a single value. That means we need four bits of storage space

0000

Each bit, when set individually, has a unique representation in decimal

0001 = 1 // or 2^0
0010 = 2 // or 2^1
0100 = 4 // or 2^2
1000 = 8 // or 2^3

A common way to implement this is with bit masks to represent each option. PHP's error levels are done this way, for example.

define( 'OPT_1', 1 );
define( 'OPT_2', 2 );
define( 'OPT_3', 4 );
define( 'OPT_4', 8 );

Then when you have an integer that represents 0 or more of these flags, you check with with the bitwise and operator which is &

$options = bindec( '0101' );
// can also be set like this
// $options = OPT_1 | OPT_3;

if ( $options & OPT_3 )
{
  // option 3 is enabled
}

This operator works as such: only bits that are set in both operands are set in the result

0101 // our options
0100 // the value of OPT_3
----
0100 // The decimal integer 4 evaluates as "true" in an expression

If we checked it against OPT_2, then the result would look like this

0101 // our options
0010 // the value of OPT_2
----
0000 // The decimal integer 0 evaluates as "false" in an expression