{"id":547,"date":"2006-06-01T21:29:29","date_gmt":"2006-06-01T19:29:29","guid":{"rendered":"http:\/\/frenchfragfactory.net\/ozh\/archives\/2006\/06\/01\/php-variables-vs-constants\/"},"modified":"2007-05-05T12:03:01","modified_gmt":"2007-05-05T10:03:01","slug":"php-variables-vs-constants","status":"publish","type":"post","link":"https:\/\/planetozh.com\/blog\/2006\/06\/php-variables-vs-constants\/","title":{"rendered":"PHP : Variables vs Constants"},"content":{"rendered":"

I thought, and had been told, that using constants<\/a> instead of variables<\/a> in PHP was mostly a matter of speed : at run time, the engine replaces every occurrence of a constant with its hard-coded value, making code presumably faster than using variables that must be evaluated each time they are encountered. Or something like this.<\/p>\n

Wondering how big or meaningless the incidence would be, and being the anal retentive useless benchmarks & statistics fan I am, I ran a few tests. With a surprise for me at the end. Bottom line : variables are faster ?!
\n<\/p>\n

Tests<\/h2>\n

To compare speed when processing some $variables, $arrays and CONSTANTS, I threw them twice into the silly formula ((sin(A * B + C))\/D * (sqrt( log(E) * abs(F – 1\/G)) \/ H)) * I<\/em><\/p>\n

    \n
  1. straight processing<\/li>\n
  2. function call and a global statement to access variables<\/li>\n<\/ol>\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. \/\/ straight processing, variables<\/span><\/div><\/li>\n
    2. for<\/span>(<\/span>$i<\/span>=<\/span>0<\/span>;<\/span>$i<\/span><<\/span>$loop<\/span>;<\/span>$i<\/span>++<\/span>)<\/span> {<\/span><\/div><\/li>\n
    3.     $test<\/span> =<\/span> (<\/span>(<\/span>sin<\/span>(<\/span>$val0<\/span> *<\/span> $val1<\/span> +<\/span> $val2<\/span>)<\/span>)<\/span>\/<\/span>$val6<\/span> *<\/span> (<\/span>sqrt<\/span>(<\/span> log<\/span>(<\/span>$val3<\/span>)<\/span> *<\/span> abs<\/span>(<\/span>$val4<\/span> -<\/span> 1<\/span>\/<\/span>$val5<\/span>)<\/span>)<\/span> \/<\/span> $val7<\/span>)<\/span>)<\/span> *<\/span> $val8<\/span>;<\/span><\/div><\/li>\n
    4. }<\/span><\/div><\/li>\n
    5.  <\/div><\/li>\n
    6. \/\/ straight processing, arrays<\/span><\/div><\/li>\n
    7. for<\/span>(<\/span>$i<\/span>=<\/span>0<\/span>;<\/span>$i<\/span><<\/span>$loop<\/span>;<\/span>$i<\/span>++<\/span>)<\/span> {<\/span><\/div><\/li>\n
    8.     $test<\/span> =<\/span> (<\/span>(<\/span>sin<\/span>(<\/span>$arrayval<\/span>&<\/span>#91;0&#93; * $arrayval&#91;1&#93; + $arrayval&#91;2&#93;))\/$arrayval&#91;6&#93; * (sqrt( log($arrayval&#91;3&#93;) * abs($arrayval&#91;4&#93; - 1\/$arrayval&#91;5&#93;)) \/ $arrayval&#91;7&#93;)) * $arrayval&#91;8&#93;;<\/span><\/div><\/li>\n
    9. }<\/span><\/div><\/li>\n
    10.  <\/div><\/li>\n
    11. \/\/ straight processing, constants<\/span><\/div><\/li>\n
    12. for<\/span>(<\/span>$i<\/span>=<\/span>0<\/span>;<\/span>$i<\/span><<\/span>$loop<\/span>;<\/span>$i<\/span>++<\/span>)<\/span> {<\/span><\/div><\/li>\n
    13.     $test<\/span> =<\/span> (<\/span>(<\/span>sin<\/span>(<\/span>VAL0 *<\/span> VAL1 +<\/span> VAL2)<\/span>)<\/span>\/<\/span>VAL6 *<\/span> (<\/span>sqrt<\/span>(<\/span> log<\/span>(<\/span>VAL3)<\/span> *<\/span> abs<\/span>(<\/span>VAL4 -<\/span> 1<\/span>\/<\/span>VAL5)<\/span>)<\/span> \/<\/span> VAL7)<\/span>)<\/span> *<\/span> VAL8;<\/span><\/div><\/li>\n
    14. }<\/span><\/div><\/li>\n
    15.  <\/div><\/li>\n
    16. \/\/ function call, variables<\/span><\/div><\/li>\n
    17. function<\/span> testvar(<\/span>$loop<\/span>)<\/span> {<\/span><\/div><\/li>\n
    18.     global<\/span> $val0<\/span>,<\/span>$val1<\/span>,<\/span>$val2<\/span>,<\/span>$val3<\/span>,<\/span>$val4<\/span>,<\/span>$val5<\/span>,<\/span>$val6<\/span>,<\/span>$val7<\/span>,<\/span>$val8<\/span>;<\/span><\/div><\/li>\n
    19.     for<\/span> (<\/span>$i<\/span>=<\/span>0<\/span>;<\/span>$i<\/span><<\/span>$loop<\/span>;<\/span>$i<\/span>++<\/span>)<\/span> {<\/span><\/div><\/li>\n
    20.         $test<\/span> =<\/span> (<\/span>(<\/span>sin<\/span>(<\/span>$val0<\/span> *<\/span> $val1<\/span> +<\/span> $val2<\/span>)<\/span>)<\/span>\/<\/span>$val6<\/span> *<\/span> (<\/span>sqrt<\/span>(<\/span> log<\/span>(<\/span>$val3<\/span>)<\/span> *<\/span> abs<\/span>(<\/span>$val4<\/span> -<\/span> 1<\/span>\/<\/span>$val5<\/span>)<\/span>)<\/span> \/<\/span> $val7<\/span>)<\/span>)<\/span> *<\/span> $val8<\/span>;<\/span><\/div><\/li>\n
    21.     }<\/span><\/div><\/li>\n
    22. }<\/span><\/div><\/li>\n
    23.  <\/div><\/li>\n
    24. \/\/ function call, array<\/span><\/div><\/li>\n
    25. function<\/span> testarr(<\/span>$loop<\/span>)<\/span> {<\/span><\/div><\/li>\n
    26.     global<\/span> $arrayval<\/span>;<\/span><\/div><\/li>\n
    27.     for<\/span> (<\/span>$i<\/span>=<\/span>0<\/span>;<\/span>$i<\/span><<\/span>$loop<\/span>;<\/span>$i<\/span>++<\/span>)<\/span> {<\/span><\/div><\/li>\n
    28.         $test<\/span> =<\/span> (<\/span>(<\/span>sin<\/span>(<\/span>$arrayval<\/span>&<\/span>#91;0&#93; * $arrayval&#91;1&#93; + $arrayval&#91;2&#93;))\/$arrayval&#91;6&#93; * (sqrt( log($arrayval&#91;3&#93;) * abs($arrayval&#91;4&#93; - 1\/$arrayval&#91;5&#93;)) \/ $arrayval&#91;7&#93;)) * $arrayval&#91;8&#93;;<\/span><\/div><\/li>\n
    29.     }<\/span><\/div><\/li>\n
    30. }<\/span><\/div><\/li>\n
    31.  <\/div><\/li>\n
    32. \/\/ function call, constants<\/span><\/div><\/li>\n
    33. function<\/span> testconst(<\/span>$loop<\/span>)<\/span> {<\/span><\/div><\/li>\n
    34.     for<\/span> (<\/span>$i<\/span>=<\/span>0<\/span>;<\/span>$i<\/span><<\/span>$loop<\/span>;<\/span>$i<\/span>++<\/span>)<\/span> {<\/span><\/div><\/li>\n
    35.         $sum<\/span> =<\/span> (<\/span>(<\/span>sin<\/span>(<\/span>VAL0 *<\/span> VAL1 +<\/span> VAL2)<\/span>)<\/span>\/<\/span>VAL6 *<\/span> (<\/span>sqrt<\/span>(<\/span> log<\/span>(<\/span>VAL3)<\/span> *<\/span> abs<\/span>(<\/span>VAL4 -<\/span> 1<\/span>\/<\/span>VAL5)<\/span>)<\/span> \/<\/span> VAL7)<\/span>)<\/span> *<\/span> VAL8;<\/span><\/div><\/li>\n
    36.     }<\/span><\/div><\/li>\n
    37. }<\/span><\/div><\/li>\n
    38. &<\/span>#91;\/php&#93;<\/span><\/div><\/li>\n
    39.  <\/div><\/li>\n
    40. (<\/span>Download the full <<\/span>a href=<\/span>"\/download\/benchmarking-constants-variables.php"<\/span>><\/span>benchmark script<\/<\/span>a><\/span>)<\/span><\/div><\/li>\n
    41.  <\/div><\/li>\n
    42. <<\/span>h2><\/span>Results<\/<\/span>h2><\/span><\/div><\/li>\n
    43.  <\/div><\/li>\n
    44. <<\/span>table cellpadding=<\/span>"5"<\/span> border=<\/span>"1"<\/span>><\/span><\/div><\/li>\n
    45. <<\/span>tr><<\/span>td>&<\/span>nbsp;<\/<\/span>td><<\/span>td><\/span>PHP 4.<\/span>4.<\/span>2<\/<\/span>td><<\/span>td><\/span>PHP 5.<\/span>1.<\/span>2<\/<\/span>td><\/<\/span>tr><\/span><\/div><\/li>\n
    46. <<\/span>tr><<\/span>td><\/span>straight,<\/span> variables<\/<\/span>td><<\/span>td><\/span>0.0382<\/span><\/<\/span>td><<\/span>td><\/span>0.0269<\/span><\/<\/span>td><\/<\/span>tr><\/span><\/div><\/li>\n
    47. <<\/span>tr><<\/span>td><\/span>straight,<\/span> array<\/<\/span>td><<\/span>td><\/span>0.0510<\/span><\/<\/span>td><<\/span>td><\/span>0.0363<\/span><\/<\/span>td><\/<\/span>tr><\/span><\/div><\/li>\n
    48. <<\/span>tr><<\/span>td><\/span>straight,<\/span> constants<\/<\/span>td><<\/span>td><\/span>0.0552<\/span><\/<\/span>td><<\/span>td><\/span>0.03848<\/span><\/<\/span>td><\/<\/span>tr><\/span><\/div><\/li>\n
    49. <<\/span>tr><<\/span>td><\/span>function<\/span> call,<\/span> variables<\/<\/span>td><<\/span>td><\/span>0.0382<\/span><\/<\/span>td><<\/span>td><\/span>0.0276<\/span><\/<\/span>td><\/<\/span>tr><\/span><\/div><\/li>\n
    50. <<\/span>tr><<\/span>td><\/span>function<\/span> call,<\/span> array<\/<\/span>td><<\/span>td><\/span>0.0462<\/span><\/<\/span>td><<\/span>td><\/span>0.0331<\/span><\/<\/span>td><\/<\/span>tr><\/span><\/div><\/li>\n
    51. <<\/span>tr><<\/span>td><\/span>function<\/span> call,<\/span> constants<\/<\/span>td><<\/span>td><\/span>0.0470<\/span><\/<\/span>td><<\/span>td><\/span>0.0388<\/span><\/<\/span>td><\/<\/span>tr><\/span><\/div><\/li>\n
    52. <\/<\/span>table><\/span><\/div><\/li>\n
    53.  <\/div><\/li>\n
    54. Hey,<\/span> where is the supposedly speed advantage of constants ? Not only using variables is faster,<\/span> but even arrays which I thought would perform worse consistently outperform constants.<\/span><\/div><\/li>\n
    55.  <\/div><\/li>\n
    56. <<\/span>h2><\/span>Conclusions<\/<\/span>h2><\/span><\/div><\/li>\n
    57.  <\/div><\/li>\n
    58. I was not able to compare memory usage across these tests,<\/span> but regarding speed I'm certainly disappointed to see how constants are doing. Of course, speed loss is probably negligible in almost if not all situations, but still.<\/span><\/div><\/li>\n
    59.  <\/div><\/li>\n
    60. Why use constants then ? Their only advantages over variables I can think of is that constant have a global scope so you can forget a global statement, and if you mistype a test (= instead of == or ===), it'<\/span>s safer to use<\/span> a constant<\/span> that cannot be redefined than a variable.<\/span> Consider the following :<\/span><\/div><\/li>\n
    61.  <\/div><\/li>\n
    62. [<\/span>php]<\/span><\/div><\/li>\n
    63. if<\/span> (<\/span>$variable<\/span> =<\/span> 1<\/span>)<\/span> {<\/span><\/div><\/li>\n
    64. \/\/ oops !<\/span><\/div><\/li>\n
    65. }<\/span><\/div><\/li>\n
    66.  <\/div><\/li>\n
    67. if<\/span> (<\/span>VARIABLE =<\/span> 1<\/span>)<\/span> {<\/span><\/div><\/li>\n
    68. \/\/ easy to spot and won't work<\/span><\/div><\/li>\n
    69. }<\/span><\/div><\/li>\n<\/ol>\t<\/div>\n\n<\/div>\n\n

      But this is slight advantage, and you're going safer anyway with a reverse syntax where typos generate a warning :<\/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. if<\/span> (<\/span>1<\/span> ==<\/span> $variable<\/span>)<\/span> {<\/span> \/\/ do stuff }<\/span><\/div><\/li>\n<\/ol>\t<\/div>\n\n<\/div>\n\n

        So, basically, I'm asking : why use constants ? Are you using them ?<\/p>\n","protected":false},"excerpt":{"rendered":"

        I thought, and had been told, that using constants instead of variables in PHP was mostly a matter of speed : at run time, the engine replaces every occurrence of a constant with its hard-coded value, making code presumably faster than using variables that must be evaluated each time they are encountered. Or something like […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[],"tags":[169,2,10,74,49],"class_list":["post-547","post","type-post","status-publish","format-standard","hentry","tag-benchmark","tag-code","tag-php","tag-stats","tag-useless"],"_links":{"self":[{"href":"https:\/\/planetozh.com\/blog\/wp-json\/wp\/v2\/posts\/547","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/planetozh.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/planetozh.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/planetozh.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/planetozh.com\/blog\/wp-json\/wp\/v2\/comments?post=547"}],"version-history":[{"count":0,"href":"https:\/\/planetozh.com\/blog\/wp-json\/wp\/v2\/posts\/547\/revisions"}],"wp:attachment":[{"href":"https:\/\/planetozh.com\/blog\/wp-json\/wp\/v2\/media?parent=547"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/planetozh.com\/blog\/wp-json\/wp\/v2\/categories?post=547"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/planetozh.com\/blog\/wp-json\/wp\/v2\/tags?post=547"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}