PHP: Tabulky porovnání datových typů v PHP

Last updated: Sat, 24 Mar 2007

Příloha Q. Tabulky porovnání datových typů v PHP

Následující tabulky ukazují chování PHP typů a porovnávacích operatorů, jak pro volné, tak pro striktní porovnávání. Tento doplněk se také vztahuje k manuálové sekci o manipulaci s typy. Inspirace byla čerpána z různých uživatelských komentářů a z práce na » BlueShoes.

Před použitím těchto tabulek je důležité pochopit typy a jejich významy. Například "42" je string (řetězec), kdežto 42 je integer (celé číslo). FALSE je boolean, kdežto "false" je string.

Poznámka: HTML formuláře nepředávají celá čísla, čísla v plovoucí řádové čárce ani pravdivostní hodnoty; předávají řetězce. Ke zjištění, zda se jedná o číselný řetězec, můžete použít funkci is_numeric().

Poznámka: Jednoduché if ($x), když $x není definováno, vygeneruje chybu úrovně E_NOTICE. Namísto toho zvolte použití empty() nebo isset() a/nebo své proměnné inicializujte.

Tabulka Q.1. Porovnání $x v PHP funkcích

Výraz	gettype()	empty()	is_null()	isset()	boolean : `if($x)`
`$x = "";`	string	`TRUE`	`FALSE`	`TRUE`	`FALSE`
`$x = NULL`	NULL	`TRUE`	`TRUE`	`FALSE`	`FALSE`
`var $x;`	NULL	`TRUE`	`TRUE`	`FALSE`	`FALSE`
`$x` není definováno	NULL	`TRUE`	`TRUE`	`FALSE`	`FALSE`
`$x = array();`	array	`TRUE`	`FALSE`	`TRUE`	`FALSE`
`$x = false;`	boolean	`TRUE`	`FALSE`	`TRUE`	`FALSE`
`$x = true;`	boolean	`FALSE`	`FALSE`	`TRUE`	`TRUE`
`$x = 1;`	integer	`FALSE`	`FALSE`	`TRUE`	`TRUE`
`$x = 42;`	integer	`FALSE`	`FALSE`	`TRUE`	`TRUE`
`$x = 0;`	integer	`TRUE`	`FALSE`	`TRUE`	`FALSE`
`$x = -1;`	integer	`FALSE`	`FALSE`	`TRUE`	`TRUE`
`$x = "1";`	string	`FALSE`	`FALSE`	`TRUE`	`TRUE`
`$x = "0";`	string	`TRUE`	`FALSE`	`TRUE`	`FALSE`
`$x = "-1";`	string	`FALSE`	`FALSE`	`TRUE`	`TRUE`
`$x = "php";`	string	`FALSE`	`FALSE`	`TRUE`	`TRUE`
`$x = "true";`	string	`FALSE`	`FALSE`	`TRUE`	`TRUE`
`$x = "false";`	string	`FALSE`	`FALSE`	`TRUE`	`TRUE`

Tabulka Q.2. Volné porovnání pomocí ==

	`TRUE`	`FALSE`	`1`	`0`	`-1`	`"1"`	`"0"`	`"-1"`	`NULL`	`array()`	`"php"`
`TRUE`	`TRUE`	`FALSE`	`TRUE`	`FALSE`	`TRUE`	`TRUE`	`FALSE`	`TRUE`	`FALSE`	`FALSE`	`TRUE`
`FALSE`	`FALSE`	`TRUE`	`FALSE`	`TRUE`	`FALSE`	`FALSE`	`TRUE`	`FALSE`	`TRUE`	`TRUE`	`FALSE`
`1`	`TRUE`	`FALSE`	`TRUE`	`FALSE`	`FALSE`	`TRUE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`
`0`	`FALSE`	`TRUE`	`FALSE`	`TRUE`	`FALSE`	`FALSE`	`TRUE`	`FALSE`	`TRUE`	`FALSE`	`TRUE`
`-1`	`TRUE`	`FALSE`	`FALSE`	`FALSE`	`TRUE`	`FALSE`	`FALSE`	`TRUE`	`FALSE`	`FALSE`	`FALSE`
`"1"`	`TRUE`	`FALSE`	`TRUE`	`FALSE`	`FALSE`	`TRUE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`
`"0"`	`FALSE`	`TRUE`	`FALSE`	`TRUE`	`FALSE`	`FALSE`	`TRUE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`
`"-1"`	`TRUE`	`FALSE`	`FALSE`	`FALSE`	`TRUE`	`FALSE`	`FALSE`	`TRUE`	`FALSE`	`FALSE`	`FALSE`
`NULL`	`FALSE`	`TRUE`	`FALSE`	`TRUE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`TRUE`	`TRUE`	`FALSE`
`array()`	`FALSE`	`TRUE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`TRUE`	`TRUE`	`FALSE`
`"php"`	`TRUE`	`FALSE`	`FALSE`	`TRUE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`TRUE`

Tabulka Q.3. Striktní porovnání pomocí ===

	`TRUE`	`FALSE`	`1`	`0`	`-1`	`"1"`	`"0"`	`"-1"`	`NULL`	`array()`	`"php"`
`TRUE`	`TRUE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`
`FALSE`	`FALSE`	`TRUE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`
`1`	`FALSE`	`FALSE`	`TRUE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`
`0`	`FALSE`	`FALSE`	`FALSE`	`TRUE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`
`-1`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`TRUE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`
`"1"`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`TRUE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`
`"0"`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`TRUE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`
`"-1"`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`TRUE`	`FALSE`	`FALSE`	`FALSE`
`NULL`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`TRUE`	`FALSE`	`FALSE`
`array()`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`TRUE`	`FALSE`
`"php"`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`TRUE`

Poznámka pro PHP 3.0: Hodnota řetězce "0" se v PHP 3 považuje za neprázdnou. V PHP 4 se toto chování změnilo a řetězec je nyní považován za prázdný.

Seznam tokenů parseru

Unixová oblast: Unix a UDG

Last updated: Sat, 24 Mar 2007

add a note User Contributed Notes
Tabulky porovnání datových typů v PHP

rich
08-May-2008 04:20


The note about object comparison should be corrected. Cloning objects does not imply instances are the same, so === would return FALSE. 



Compare object

<?php

$o = new stdClass();

$o->we = 12;



$o2 = new stdClass();

$o2->we = 12;



$o3 = clone $o2;

var_dump($o == $o2); //true

var_dump($o === $o2); //false

var_dump($o3 === $o2); //false

?>

gernovich at ya dot ru
08-May-2008 09:48


Universal comparison test.



<?php



$tests = array();

$tests['==']  = create_function('$a, $b', 'return $a==$b;');

$tests['==='] = create_function('$a, $b', 'return $a===$b;');

$tests['!='] = create_function('$a, $b', 'return $a!=$b;');

$tests['<>'] = create_function('$a, $b', 'return $a<>$b;');

$tests['!=='] = create_function('$a, $b', 'return $a!==$b;');

$tests['<']   = create_function('$a, $b', 'return $a<$b;');

$tests['>']   = create_function('$a, $b', 'return $a>$b;');

$tests['<=']  = create_function('$a, $b', 'return $a<=$b;');

$tests['>=']  = create_function('$a, $b', 'return $a>=$b;');



$comparison = array();

$comparison['TRUE'] = true;

$comparison['FALSE'] = false;

$comparison['1'] = 1;

$comparison['0'] = 0;

$comparison['-1'] = -1;

$comparison['3,14'] = pi();

$comparison['"1"'] = '1';

$comparison['"0"'] = '0';

$comparison['"-1"'] = '-1';

$comparison['NULL'] = null;

$comparison['array()'] = array();

$comparison['"php"'] = 'php';

        

print '<h1>PHP version '.PHP_VERSION.' type comparison tables</h1>';

        

foreach ($tests as $test=>$function) {

    print "<h2>Comparisons with $test</h2>";

    print "<table border='1'>";

    print "<tr>";

    print "<th>&nbsp;</th>";

    foreach (array_keys($comparison) as $name) {

        print "<th>$name</th>";

    }

    print "</tr>";

    foreach ($comparison as $arg_1_name => $arg_1_value) {

        print '<tr>';

        print "<th>$arg_1_name</th>";

        foreach ($comparison as $arg_2_value) {

            print '<td>';

            print $function($arg_1_value, $arg_2_value)==true ?

                        '<span style="color:#00F;">TRUE</span>' : '<span style="color:#F00;">FALSE</span>';

            print '</td>';

        }

        print "</tr>";

    }

    print "</table>";

}



?>

info at shaelf dot ru
06-Jan-2008 10:51


Compare object

<?php

$o = new stdClass();

$o->we = 12;



$o2 = new stdClass();

$o2->we = 12;



$o3 = clone $o2;

var_dump($o == $o2); //true

var_dump($o === $o2); //false

var_dump($o3 === $o2); //true

?>

frank
15-Aug-2007 12:06


A comparison table for <=,<,=>,> would be nice...

Following are TRUE (tested PHP4&5):

NULL <= -1

NULL <= 0

NULL <= 1

!(NULL >= -1)

NULL >= 0

!(NULL >= 1)

That was a surprise for me (and it is not like SQL, I would like to have the option to have SQL semantics with NULL...).

15-Mar-2007 11:06


Re: omit's comment



The note omit quotes is referring to the VALUE returned, not its name. If you put 42 into a text field, the corresponding array value will be the string "42". The note makes no comment on the array's keys.

omit
23-Aug-2006 08:32


the manual said "HTML Forms do not pass integers, floats, or booleans; they pass strings"



while this is true, php will sometimes change the type to either type array, or possibly type integer(no, not a numeric string) if it was used as an array key. php seems to do this when it parses the request data into the predefined variable arrays.



example:



<input type="text" name="foo[5]">

<input type="text" name="foo[7]">



now obviously the browser will send those names as a string. but php will change thier type.



<?php



// $_POST['foo'] is an array

var_dump($_POST['foo']);



foreach ($_POST['foo'] as $key => $val) {

    // the keys 5 and 7 will be type integer

    var_dump($key);

}



?>



because of this, its also a good idea to check the types of your variables.

Jan
29-Dec-2005 08:23


Note that php comparison is not transitive:



"php" == 0 => true

0 == null => true

null == "php" => false

php [at] barryhunter [.] co [.] uk
07-Sep-2005 09:44


In case it helps someone, here's a table to compare different Variable tests (created before I found this page!)



http://www.deformedweb.co.uk/php_variable_tests.php

jerryschwartz at comfortable dot com
26-Jul-2005 10:04


In some languages, a boolean is promoted to an integer (with a value of 1 or -1, typically) if used in an expression with an integer. I found that PHP has it both ways:



If you add a boolean with a value of true to an integer with a value of 3, the result will be 4 (because the boolean is cast as an integer).



On the other hand, if you test a boolean with a value of true for equality with an integer with a value of three, the result will be true (because the integer is cast as a boolean).



Surprisingly, at first glance, if you use either < or > as the comparison operator the result is always false (again, because the integer as cast as a boolean, and true is neither greater nor less than true).

tom
17-Jun-2005 11:27


<?php


if (strlen($_POST['var']) > 0) {


    // form value is ok


}


?>





When working with HTML forms this a good way to:





(A) let "0" post values through like select or radio values that correspond to array keys or checkbox booleans that would return FALSE with empty(), and;


(B) screen out $x = "" values, that would return TRUE with isset()!





Because HTML forms post values as strings, this is a good way to test variables!





[[Editor Note: This will create a PHP Error of level E_NOTICE if the checked variable (in this case $_POST['var']) is undefined. It may be used after (in conjuection with) isset() to prevent this.]]

aidan at php dot net
24-Jan-2005 04:00


The way PHP handles comparisons when multiple types are concerned is quite confusing.



For example:

"php" == 0



This is true, because the string is casted interally to an integer. Any string (that does not start with a number), when casted to an integer, will be 0.

add a note

Seznam tokenů parseru

Unixová oblast: Unix a UDG

Last updated: Sat, 24 Mar 2007