Question

I saw in school a system that set permissions using binary string.

Let’s say 101001 = 41

So :

• 1 can be permission to page 1
• 2 can be permission to page 2
• 4 can be permission to page 3
• 8 can be permission to page 4
• 16 can be permission to page 5
• 32 can be permission to page 6

So let’s say I got the above binary string (101001). I have access to page 1, 4 and 6.

How can I do this in PHP ? Let’s say I got a field in MySQL named perms stored in dec so 101001 will be 41. How can I know that 41 is equal to 1, 8 and 32 in PHP ?

Thanks.

Answer 1

Sounds like you’re talking about bits and bit-wise operators. This easiest way to set this up is to define constants for every permission

const POST   = 1;
const DELETE = 2;
const UPDATE = 4;
const READ   = 8;

Once you have these defined it’s easy to make comparisons using the bitwise operators:

$userValue = '1101';

if ($userValue & self::POST) {
  echo 'Can Post';
}

if ($userValue & self::DELETE) {
  echo 'Can Delete';
}

if ($userValue & self::UPDATE) {
  echo 'Can Update';
}

if ($userValue & self::READ) {
  echo 'Can Read';
}

This is how many of PHP’s own constants work. If you’ve ever set the error reporting using something like E_ALL & E_DEPRECATED you’re actually working with binary numbers.