{"id":538,"date":"2006-05-12T20:57:51","date_gmt":"2006-05-12T18:57:51","guid":{"rendered":"http:\/\/frenchfragfactory.net\/ozh\/archives\/2006\/05\/12\/538\/"},"modified":"2007-05-08T15:51:06","modified_gmt":"2007-05-08T13:51:06","slug":"php-bitwise-operators-example-of-use","status":"publish","type":"post","link":"https:\/\/planetozh.com\/blog\/2006\/05\/php-bitwise-operators-example-of-use\/","title":{"rendered":"PHP Bitwise Operators Example of Use"},"content":{"rendered":"

In my neverending amateur journey through the wonders of coding, here is something I've learnt in PHP today : how to conveniently store a set of flags into one value, with bitmask comparisons made easy thanks to PHP bitwise operators<\/a>. Sounds greek to you ? Read on, it's this kind of things that are piece of cake to use while they still make you look brilliant when you explain it to your wife.
\n<\/p>\n

Example of use<\/h2>\n

Say you're making a WordPress theme and want to give users control over whether a particular block should be in left sidebar or right sidebar (if displayed at all). To do so you've set up this kind of form :<\/p>\n

\"Sort<\/p>\n

First : DEFINE<\/h2>\n

First, define a set of constants<\/p>\n

<?php\r\ndefine('BLOCK_ARCHIVES'\t, 1);\r\ndefine('BLOCK_CALENDAR'\t, BLOCK_ARCHIVES << 1);\r\ndefine('BLOCK_LASTCOM'\t, BLOCK_ARCHIVES << 2);\r\ndefine('BLOCK_QUOTE'\t, BLOCK_ARCHIVES << 3);\r\ndefine('BLOCK_CCNUMBER'\t, BLOCK_ARCHIVES << 4);\r\ndefine('BLOCK_BABE'\t, BLOCK_ARCHIVES << 5);\r\ndefine('BLOCK_ADMIN'\t, BLOCK_ARCHIVES << 6);\r\n?><\/code><\/pre><\/div>\n
All these constants now have the following values : 1, 2, 4, 8, 16, 32, 64 (powers of 2).<\/p>\n
Now use<\/h2>\n
Once the user submits the form in the above screenshot, you would create and store two values, something like :<\/p>\n
<?php\r\n$display_left = BLOCK_ARCHIVES | BLOCK_QUOTE | BLOCK_ADMIN;\r\n$display_right = BLOCK_CALENDAR | BLOCK_LASTCOM | BLOCK_BABE;\r\n?><\/code><\/pre><\/div>\n
The beauty of it is that, no matter how many options you have, you just need to store 2 integers to remember them all.<\/p>\n
Testing whether a block should display left, right or nowhere is now easy :<\/p>\n
<?php\r\nif (constant($block) === ($display_left & constant($block))) {\r\n       echo "$block goes left";\r\n} elseif (constant($block) === ($display_right & constant($block))) {\r\n       echo "$block goes right";\r\n} else {\r\n       echo "$block goes \/dev\/null";\r\n}\r\n?><\/code><\/pre><\/div>\n
Testing the above code with $block = 'BLOCK_ARCHIVES'<\/strong> would for example echo BLOCK_ARCHIVES goes left<\/strong>. Easy, isn't it ?<\/p>\n
Other ideas of use<\/h2>\n
Really, this trick is a useful one. You could imagine storing a lot of things this way :<\/p>\n