{"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<\/div><\/li>\n
    2. for($i=0;$i<$loop;$i++) {<\/div><\/li>\n
    3.     $test = ((sin($val0 * $val1 + $val2))\/$val6 * (sqrt( log($val3) * abs($val4 - 1\/$val5)) \/ $val7)) * $val8;<\/div><\/li>\n
    4. }<\/div><\/li>\n
    5.  <\/div><\/li>\n
    6. \/\/ straight processing, arrays<\/div><\/li>\n
    7. for($i=0;$i<$loop;$i++) {<\/div><\/li>\n
    8.     $test = ((sin($arrayval&#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;)) * $arrayval&#91;8&#93;;<\/div><\/li>\n
    9. }<\/div><\/li>\n
    10.  <\/div><\/li>\n
    11. \/\/ straight processing, constants<\/div><\/li>\n
    12. for($i=0;$i<$loop;$i++) {<\/div><\/li>\n
    13.     $test = ((sin(VAL0 * VAL1 + VAL2))\/VAL6 * (sqrt( log(VAL3) * abs(VAL4 - 1\/VAL5)) \/ VAL7)) * VAL8;<\/div><\/li>\n
    14. }<\/div><\/li>\n
    15.  <\/div><\/li>\n
    16. \/\/ function call, variables<\/div><\/li>\n
    17. function testvar($loop) {<\/div><\/li>\n
    18.     global $val0,$val1,$val2,$val3,$val4,$val5,$val6,$val7,$val8;<\/div><\/li>\n
    19.     for ($i=0;$i<$loop;$i++) {<\/div><\/li>\n
    20.         $test = ((sin($val0 * $val1 + $val2))\/$val6 * (sqrt( log($val3) * abs($val4 - 1\/$val5)) \/ $val7)) * $val8;<\/div><\/li>\n
    21.     }<\/div><\/li>\n
    22. }<\/div><\/li>\n
    23.  <\/div><\/li>\n
    24. \/\/ function call, array<\/div><\/li>\n
    25. function testarr($loop) {<\/div><\/li>\n
    26.     global $arrayval;<\/div><\/li>\n
    27.     for ($i=0;$i<$loop;$i++) {<\/div><\/li>\n
    28.         $test = ((sin($arrayval&#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;)) * $arrayval&#91;8&#93;;<\/div><\/li>\n
    29.     }<\/div><\/li>\n
    30. }<\/div><\/li>\n
    31.  <\/div><\/li>\n
    32. \/\/ function call, constants<\/div><\/li>\n
    33. function testconst($loop) {<\/div><\/li>\n
    34.     for ($i=0;$i<$loop;$i++) {<\/div><\/li>\n
    35.         $sum = ((sin(VAL0 * VAL1 + VAL2))\/VAL6 * (sqrt( log(VAL3) * abs(VAL4 - 1\/VAL5)) \/ VAL7)) * VAL8;<\/div><\/li>\n
    36.     }<\/div><\/li>\n
    37. }<\/div><\/li>\n
    38. &#91;\/php&#93;<\/div><\/li>\n
    39.  <\/div><\/li>\n
    40. (Download the full <a href="\/download\/benchmarking-constants-variables.php">benchmark script<\/a>)<\/div><\/li>\n
    41.  <\/div><\/li>\n
    42. <h2>Results<\/h2><\/div><\/li>\n
    43.  <\/div><\/li>\n
    44. <table cellpadding="5" border="1"><\/div><\/li>\n
    45. <tr><td>&nbsp;<\/td><td>PHP 4.4.2<\/td><td>PHP 5.1.2<\/td><\/tr><\/div><\/li>\n
    46. <tr><td>straight, variables<\/td><td>0.0382<\/td><td>0.0269<\/td><\/tr><\/div><\/li>\n
    47. <tr><td>straight, array<\/td><td>0.0510<\/td><td>0.0363<\/td><\/tr><\/div><\/li>\n
    48. <tr><td>straight, constants<\/td><td>0.0552<\/td><td>0.03848<\/td><\/tr><\/div><\/li>\n
    49. <tr><td>function call, variables<\/td><td>0.0382<\/td><td>0.0276<\/td><\/tr><\/div><\/li>\n
    50. <tr><td>function call, array<\/td><td>0.0462<\/td><td>0.0331<\/td><\/tr><\/div><\/li>\n
    51. <tr><td>function call, constants<\/td><td>0.0470<\/td><td>0.0388<\/td><\/tr><\/div><\/li>\n
    52. <\/table><\/div><\/li>\n
    53.  <\/div><\/li>\n
    54. Hey, where is the supposedly speed advantage of constants ? Not only using variables is faster, but even arrays which I thought would perform worse consistently outperform constants.<\/div><\/li>\n
    55.  <\/div><\/li>\n
    56. <h2>Conclusions<\/h2><\/div><\/li>\n
    57.  <\/div><\/li>\n
    58. I was not able to compare memory usage across these tests, 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.<\/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's safer to use a constant that cannot be redefined than a variable. Consider the following :<\/div><\/li>\n
    61.  <\/div><\/li>\n
    62. [php]<\/div><\/li>\n
    63. if ($variable = 1) {<\/div><\/li>\n
    64. \/\/ oops !<\/div><\/li>\n
    65. }<\/div><\/li>\n
    66.  <\/div><\/li>\n
    67. if (VARIABLE = 1) {<\/div><\/li>\n
    68. \/\/ easy to spot and won't work<\/div><\/li>\n
    69. }<\/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 (1 == $variable) { \/\/ do stuff }<\/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 this. Wondering how big or\u2026<\/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}]}}