{"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

\n\n\t\t
\n\n\t\t
\n\t\t\t\t\t\t< View plain text<\/span> ><\/a>\n\t\t\t\t\t<\/div>\n\n\t\t
php<\/div>\n\n\t\t\n\t\t
\n\n\t<\/div>\n\t\n\t
\n\t\t
  1. <?php<\/span><\/div><\/li>\n
  2. define<\/span>(<\/span>'BLOCK_ARCHIVES'<\/span> ,<\/span> 1<\/span>)<\/span>;<\/span><\/div><\/li>\n
  3. define<\/span>(<\/span>'BLOCK_CALENDAR'<\/span> ,<\/span> BLOCK_ARCHIVES <<<\/span> 1<\/span>)<\/span>;<\/span><\/div><\/li>\n
  4. define<\/span>(<\/span>'BLOCK_LASTCOM'<\/span>  ,<\/span> BLOCK_ARCHIVES <<<\/span> 2<\/span>)<\/span>;<\/span><\/div><\/li>\n
  5. define<\/span>(<\/span>'BLOCK_QUOTE'<\/span>    ,<\/span> BLOCK_ARCHIVES <<<\/span> 3<\/span>)<\/span>;<\/span><\/div><\/li>\n
  6. define<\/span>(<\/span>'BLOCK_CCNUMBER'<\/span> ,<\/span> BLOCK_ARCHIVES <<<\/span> 4<\/span>)<\/span>;<\/span><\/div><\/li>\n
  7. define<\/span>(<\/span>'BLOCK_BABE'<\/span> ,<\/span> BLOCK_ARCHIVES <<<\/span> 5<\/span>)<\/span>;<\/span><\/div><\/li>\n
  8. define<\/span>(<\/span>'BLOCK_ADMIN'<\/span>    ,<\/span> BLOCK_ARCHIVES <<<\/span> 6<\/span>)<\/span>;<\/span><\/div><\/li>\n
  9. ?><\/span><\/div><\/li>\n<\/ol>\t<\/div>\n\n<\/div>\n\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

    \n\n\t\t
    \n\n\t\t
    \n\t\t\t\t\t\t< View plain text<\/span> ><\/a>\n\t\t\t\t\t<\/div>\n\n\t\t
    php<\/div>\n\n\t\t\n\t\t
    \n\n\t<\/div>\n\t\n\t
    \n\t\t
    1. <?php<\/span><\/div><\/li>\n
    2. $display_left<\/span> =<\/span> BLOCK_ARCHIVES |<\/span> BLOCK_QUOTE |<\/span> BLOCK_ADMIN;<\/span><\/div><\/li>\n
    3. $display_right<\/span> =<\/span> BLOCK_CALENDAR |<\/span> BLOCK_LASTCOM |<\/span> BLOCK_BABE;<\/span><\/div><\/li>\n
    4. ?><\/span><\/div><\/li>\n<\/ol>\t<\/div>\n\n<\/div>\n\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

      \n\n\t\t
      \n\n\t\t
      \n\t\t\t\t\t\t< View plain text<\/span> ><\/a>\n\t\t\t\t\t<\/div>\n\n\t\t
      php<\/div>\n\n\t\t\n\t\t
      \n\n\t<\/div>\n\t\n\t
      \n\t\t
      1. <?php<\/span><\/div><\/li>\n
      2. if<\/span> (<\/span>constant<\/span>(<\/span>$block<\/span>)<\/span> ===<\/span> (<\/span>$display_left<\/span> &<\/span> constant<\/span>(<\/span>$block<\/span>)<\/span>)<\/span>)<\/span> {<\/span><\/div><\/li>\n
      3.        echo<\/span> "$block<\/span> goes left"<\/span>;<\/span><\/div><\/li>\n
      4. }<\/span> elseif<\/span> (<\/span>constant<\/span>(<\/span>$block<\/span>)<\/span> ===<\/span> (<\/span>$display_right<\/span> &<\/span> constant<\/span>(<\/span>$block<\/span>)<\/span>)<\/span>)<\/span> {<\/span><\/div><\/li>\n
      5.        echo<\/span> "$block<\/span> goes right"<\/span>;<\/span><\/div><\/li>\n
      6. }<\/span> else<\/span> {<\/span><\/div><\/li>\n
      7.        echo<\/span> "$block<\/span> goes \/dev\/null"<\/span>;<\/span><\/div><\/li>\n
      8. }<\/span><\/div><\/li>\n
      9. ?><\/span><\/div><\/li>\n<\/ol>\t<\/div>\n\n<\/div>\n\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