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There are a lot of instances where a program or script will need to work with multiple users. Most of the time, users will need to have certain permissions (for example, a normal user and an administrator).

Lot’s of developers feel the need to make a huge database table with all these “can_*” fields as the permissions. But there’s an easier (and cleaner) way of doing this. All it takes is one integer field in your table.

You can represent a bunch of “on/off” permissions using one number and bit operators. Let’s take the user example. We could have permissions for access to the ACP, posting, uploading and deleting. We just assign a bit value (1, 2, 4, 8, 16, 32 etc):

In PHP, I’d just make an array:

Now all you have to do is add up all the permissions that you want the user to have. Here are two examples:

So you have a final value, all you have to do is use bit operators to test if a user is allowed to do whatever you want. In PHP, you would use a single ampersand character (read here). Here is a couple of examples:

The basic statement is test_against & test_with. The & operator checks for bits set in both the numbers on either side of it. So in a normal users permission of 6, the ‘can_delete’ bit of 8 is not found. Neither is the ‘is_admin’ bit of 1 found, so both of those are false.

It might be a little hard to grasp, but it saves a lot of hard work!

This entry was posted on Wednesday, September 29th, 2004 at 5:12 pm and is filed under Dev. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.