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PHP 类型比较表

以下的表格显示了 PHP 类型和比较运算符在松散和严格比较时的作用。该补充材料还和类型戏法的相关章节内容有关。同时，大量的用户注释和 » BlueShoes 的工作也给该材料提供了帮助。

在使用这些表格之前，需要明白变量类型及它们的意义。例如，"42" 是一个字符串而 42 是一个整数。FALSE 是一个布尔值而 "false" 是一个字符串。

Note:

HTML 表单并不传递整数、浮点数或者布尔值，它们只传递字符串。要想检测一个字符串是不是数字，可以使用 is_numeric() 函数。

Note:

在没有定义变量 $x 的时候，诸如 if ($x) 的用法会导致一个 E_NOTICE 级别的错误。所以，可以考虑用 empty() 或者 isset() 函数来初始化变量。

使用 PHP 函数对变量 $x 进行比较
表达式 gettype() empty() is_null() isset() boolean : if($x)
$x = ""; string TRUE FALSE TRUE FALSE
$x = null; NULL TRUE TRUE FALSE FALSE
var $x; NULL TRUE TRUE FALSE FALSE
$x is undefined 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

松散比较 ==
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 FALSE TRUE FALSE TRUE FALSE FALSE TRUE FALSE TRUE TRUE FALSE TRUE
1 TRUE FALSE TRUE FALSE FALSE TRUE FALSE FALSE FALSE FALSE FALSE FALSE
0 FALSE TRUE FALSE TRUE FALSE FALSE TRUE FALSE TRUE FALSE TRUE TRUE
-1 TRUE FALSE FALSE FALSE TRUE FALSE FALSE TRUE FALSE FALSE FALSE FALSE
"1" TRUE FALSE TRUE FALSE FALSE TRUE FALSE FALSE FALSE FALSE FALSE FALSE
"0" FALSE TRUE FALSE TRUE FALSE FALSE TRUE FALSE FALSE FALSE FALSE FALSE
"-1" TRUE FALSE FALSE FALSE TRUE FALSE FALSE TRUE FALSE FALSE FALSE FALSE
NULL FALSE TRUE FALSE TRUE FALSE FALSE FALSE FALSE TRUE TRUE FALSE TRUE
array() FALSE TRUE FALSE FALSE FALSE FALSE FALSE FALSE TRUE TRUE FALSE FALSE
"php" TRUE FALSE FALSE TRUE FALSE FALSE FALSE FALSE FALSE FALSE TRUE FALSE
"" FALSE TRUE FALSE TRUE FALSE FALSE FALSE FALSE TRUE FALSE FALSE TRUE

严格比较 ===
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 FALSE TRUE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
1 FALSE FALSE TRUE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
0 FALSE FALSE FALSE TRUE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
-1 FALSE FALSE FALSE FALSE TRUE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
"1" FALSE FALSE FALSE FALSE FALSE TRUE FALSE FALSE FALSE FALSE FALSE FALSE
"0" FALSE FALSE FALSE FALSE FALSE FALSE TRUE FALSE FALSE FALSE FALSE FALSE
"-1" FALSE FALSE FALSE FALSE FALSE FALSE FALSE TRUE FALSE FALSE FALSE FALSE
NULL FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE TRUE FALSE FALSE FALSE
array() FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE TRUE FALSE FALSE
"php" FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE TRUE FALSE
"" FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE TRUE

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PHP手册 - N: PHP 类型比较表

用户评论:

Jouriy LYSENKO (17-Jun-2011 10:18)

If $var not declared.

In php 5.2 :
<?php if($var) ?> - work

in php 5.3 :
<?php if($var) ?> - dont work and generate error E_NOTICE

mauritsdajong at gmail dot com (18-Feb-2011 03:12)

When we're doing loose comparisons (with double equals signs), the following fact is interesting.

false == array() evaluates to true
false == "" evaluates to true
array() == "" however, evaluates to false

php at benizi dot com (15-Feb-2010 06:31)

It's interesting to note that 'empty()' and 'boolean : if($x)'
are paired as logical opposites, as are 'is_null()' and 'isset()'.

edgar at goodforall dot eu (15-Dec-2009 02:55)

Some function to write out your own comparisson table in tsv format. Can be easily modified to add more testcases and/or binary functions. It will test all comparables against each other with all functions.

<?php
$funcs = array(
        /* Testing equality */
        'eq' => '==',
        'ne' => '!=',
        'gt' => '>',
        'lt' => '<',
        'ne2' => '<>',
        'lte' => '<=',
        'gte' => '>=',
        /* Testing identity */
        'id' => '===',
        'nid' => '!=='
);
class Test {
        protected $a;
        public $b;
        public function __construct($a,$b){
                $this->a = $a;
                $this->b = $b;
        }
        public function getab(){
                return $this->a.",". $this->b;
        }

}
$tst1 = new Test(1,2);
$tst2 = new Test(1,2);
$tst3 = new Test(2,2);
$tst4 = new Test(1,1);

$arr1 = array(1,2,3);
$arr2 = array(2,3,4);
$arr3 = array('a','b','c','d');
$arr4 = array('a','b','c');
$arr5 = array();

$comp1 = array(
        'ints' => array(-1,0,1,2),
        'floats' => array(-1.1,0.0,1.1,2.0),
        'string' => array('str', 'str1', '', '1'),
        'bools' => array(true, false),
        'null' => array(null),
        'objects' => array($tst1,$tst2,$tst3,$tst4),
        'arrays' => array($arr1, $arr2, $arr3, $arr4, $arr5)
);
$fbody = array();

foreach($funcs as $name => $op){
        $fbody[$name] = create_function('$a,$b', 'return $a ' . $op . ' $b;');
}

$table = array(array('function', 'comp1', 'comp2', 'f comp1 comp2', 'type'));
/* Do comparisons */
$comp2  = array();
foreach($comp1 as $type => $val){
        $comp2[$type] = $val;
}

foreach($comp1 as $key1 => $val1){
        foreach($comp2 as $key2 => $val2){
                addTableEntry($key1, $key2, $val1, $val2);
        }
}
$out = '';
foreach($table as $row){
        $out .= sprintf("%-20s\t%-20s\t%-20s\t%-20s\t%-20s\n", $row[0], $row[1], $row[2], $row[3], $row[4]);
}

print $out;
exit;

function addTableEntry($n1, $n2, $comp1, $comp2){
        global $table, $fbody;
        foreach($fbody as $fname => $func){
                        foreach($comp1 as $val1){
  foreach($comp2 as $val2){
                                        $val = $func($val1,$val2);
                                                $table[] = array($fname, gettype($val1) . ' => ' . sprintval($val1), gettype($val2) .' => ' . sprintval($val2), gettype($val) . ' => ' . sprintval($val), gettype($val1) . "-" . gettype($val2) . '-' . $fname);
                                        }
                        }
        }
}

function sprintval($val){
        if(is_object($val)){
                return 'object-' . $val->getab();
        }
        if(is_array($val)){
                return implode(',', $val);
        }
        if(is_bool($val)){
                if($val){
                        return 'true';
                }
                return 'false';
        }
        return strval($val);
}

?>

rich (08-May-2008 03:20)

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 08:48)

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 09:51)

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 (14-Aug-2007 11:06)

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 10:06)

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 07:32)

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 07:23)

Note that php comparison is not transitive:

"php" == 0 => true
0 == null => true
null == "php" => false

jerryschwartz at comfortable dot com (26-Jul-2005 09:04)

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 10:27)

<?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 03:00)

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.