PHP 类型比较表

crazy888s at hotmail dot com (2012-12-14 18:14:32)

PHP's loose comparisons can be a huge convenience when used properly! It's extremely helpful to just remember the following are always FALSE:
null, false, "", 0, "0", array()
If your application never depends on a particular "empty/false/null/0/not set" value type, you won't have to worry about 99% of the other weird cases listed here. You won't need empty() or isset(). And ALL variable types will always work as expected for statements like:
if(boolean && !string){...}
if(array){...}
if(!null || int){...}
Consider the same when working with your database values.

php at richardneill dot org (2012-04-12 19:45:28)

Be wary of string-comparison where both strings might be interpreted as numbers. Eg:
$x="123456789012345678901234567890"; $y="123456789012345678900000000000";
echo ($x==$y)?"equal":"not_equal"; #Prints equal !!
Both strings are getting converted to floats, then losing precision, then becoming equal :-(
Using "===" or making either of the strings non-numeric will prevent this.
[This is on a 32-bit machine, on a 64-bit, you will have to make the strings longer to see the effect]

Jouriy LYSENKO (2011-06-17 02:18:19)

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 (2011-02-18 07:12:13)

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 (2010-02-15 10:31:09)

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 (2009-12-15 06:55:54)

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 (2008-05-08 07:20:34)

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 (2008-05-08 00:48:41)

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 (2008-01-06 13:51:14)

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 (2007-08-14 15:06:35)

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...).

(2007-03-15 14:06:25)

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 (2006-08-23 11:32:17)

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 (2005-12-29 11:23:21)

Note that php comparison is not transitive:
"php" == 0 => true
0 == null => true
null == "php" => false

jerryschwartz at comfortable dot com (2005-07-26 13:04:32)

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 (2005-06-17 02:27:52)

<?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 (2005-01-24 07:00:06)

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.