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。

Note:

某些数值操作会导致一个特殊值，可以用常量 NAN 表示。 无论是松散还是严格比较，这个值和其他任意值（包括它自身，但排除 true）比较时都会产生 false 的结果， 例如 NAN != NAN 和 NAN !== NAN。 导致 NAN 的操作例子包括 sqrt(-1)、asin(2)、 acosh(0)。

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 = array('a', 'b'); array false false true true
$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

User Contributed Notes

Anonymous 17-Nov-2020 02:24
I noticed that some "magic" also happens when comparing strings with leading zeros with only two equal signs:

<?php
var_dump('1' == '01');
var_dump('01' == '000001');
?>

Output:
bool(true)
bool(true)

If the string contains only numbers all leading zeroes seem to be ignored.
TrickyFoxy 02-Jan-2020 08:25
<?php
echo md5('240610708') == md5('QNKCDZO') ? "equal" : "not equal"; // prints equal!!!
php at ckls dot net 20-Aug-2018 02:50
regarding the editors note in php at richardneill dot org note:
[Editor's note: As of PHP 5.4.4 this is no longer true. Integral strings that overflow into floating point numbers will no longer be considered equal.]

While this is true, there is still the following behaviour:
<?php
$x = "1";
$y = "+1";
var_dump($x == $x);
?>
outputs "bool(true)". 
So still be wary of string-comparison where both strings might be interpreted as numbers.
mark at theanti dot social 29-Mar-2018 08:59
There is also 0.0 which is not identical to 0.

  $x = 0.0;
  gettype($x); // double
  empty($x); // true
  is_null($x); //false
  isset($x); // true
  is_numeric($x); // true
  $x ? true : false; // false
  $x == 0; // true
  $x == "0"; // true
  $x == "0.0"; // true
  $x == false; // true
  $x == null; // true
  $x === 0; // false
  $x === false; // false
  $x === null; // false
  $x === "0"; // false
  $x === "0.0"; // false
alt dot jl-3gi8b7l at binich dot com 10-Mar-2018 03:41
Here's how PHP handles loose and strict comparisons of default parameters in functions:

Very unintuitive:

<?php
function f($x='surprise')
    {
    if ($x == 'surprise')
        return $x; // returns 0 !!
    }
   
echo f(0);
?>

Here some further tests:

<?php
function f($x='surprise')
    {
    if ($x == 'surprise')
        return 'A:'.$x;
    if ($x === 'surprise')
        return 'B:'.$x;
    return 'C:'.$x;
    }
   
echo "\n".f(0); // A:0 !!
echo "\n".f(0.0); // A:0 !!
echo "\n".f(NULL); // C: !!
echo "\n".f(FALSE); // C:
echo "\n".f(); // A:surprise
echo "\n".f(''); // C:
echo "\n".f((integer)0); // A:0
echo "\n".f((string)0); // C:0
echo "\n".f('0'); // C:0
echo "\n".f(0.1); // C:0.1
echo "\n".f(array()); // C:Array
echo "\n".f('surprise'); // A:surprise
?>
biziclop at vipmail dot hu 12-Aug-2017 08:57
Want to strictly compare integers that may or may not be converted to floats (via PHPExcel import/export, etc.)? You are out of luck:

var_dump(   (int)1 ===   (int)1 ); // bool(true)
var_dump( (float)1 === (float)1 ); // bool(true)
var_dump( (float)1 ===   (int)1 ); // bool(false)
var_dump(   (int)1 === (float)1 ); // bool(false)

This slightly complicated function might help you:

function equal_numbers( $a, $b ){
  if( $a === $b )  return true;
  if(   is_int( $a ) && is_float( $b ))  return (float)$a === $b && $a ===   (int)$b;
  if( is_float( $a ) &&   is_int( $b ))  return   (int)$a === $b && $a === (float)$b;
  return false;
}

Here are some tests:

test(100, 100.0 ); // int(100) float(100) bool(true)
test(  0,  -0   ); // int(0)   int(0)     bool(true)
test( -0,  -0.0 ); // int(0)   float(-0)  bool(true)
test(  0, 1/0   ); // int(0)   float(INF) bool(false)
test(  0, acos(2));// int(0)   float(NAN) bool(false)
test(       PHP_INT_MAX * 10, 0 );             //float(92233720368547758080) int(0) bool(false)
test((float)PHP_INT_MAX,     PHP_INT_MAX     );//float(9223372036854775808)  int(9223372036854775807) bool(false)
test((float)PHP_INT_MAX / 2, PHP_INT_MAX / 2 );//float(4611686018427387904)  float(4611686018427387904) bool(true)

function test( $a, $b ){
  var_dump( $a, $b, equal_numbers( $a, $b ));
}
engineer dot morozov at gmail dot com 07-Feb-2016 03:23
If you want to calculate how much more/less items by the criterion

Example:

in loop:
$counter += intval($item->isValid()) <=> 0.5;

if $counter >= 0 - valid items are more then invalid on $counter
if $counter  < 0 - valid items are less then invalid on $counter
trexx68 25-Apr-2015 05:11
If you want to view the truth tables colorized, just:

1. Save a local copy of this page as an .html file,
2. View the page source with any text editor.
3. Replace the opening <head> tag so it will include this:

<head>
  <script src="https://code.jquery.com/jquery-1.10.2.js"></script>

4. Replace the closing </body> tag with this:

  <script>
    $( "td:contains('FALSE')" ).css("color", "red");
    $( "td:contains('TRUE')" ).css("color", "green");
  </script>
</body>

5. Save the file, and view it on your browser.  Enjoy.
aravind dot a dot padmanabhan at gmail dot com 22-Apr-2015 02:31
please note that
 
$x = 0.0 ;
print empty($x); // returns 1 (true)

$x = "0.0";
print empty($x); // returns blank (false);
Anonymous 16-Oct-2014 06:19
The loose comparison chart is missing a few things.

array(1)==true returns true.

also:

(int)array(1) === 1 returns true

This is symmetric:

array(1) === (array)1 returns true

but the loose comparison

array(1)==1 still returns false.
blue dot hirano at gmail dot com 07-Sep-2014 02:29
The truth tables really ought to be colorized; they're very hard to read as they are right now (just big arrays of TRUE and FALSE).

Also, something to consider: clustering the values which compare similarly (like is done on qntm.org/equality) would make the table easier to read as well. (This can be done simply by hand by rearranging the order of headings to bring related values closer together).
Anonymous 21-Nov-2013 01:43
I'm running PHP 5.5.3.

This is a correction to one of the previous posts.

<?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
?>

Output is:

true, false, false
crazy888s at hotmail dot com 14-Dec-2012 06:14
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 12-Apr-2012 07:45
[Editor's note: As of PHP 5.4.4 this is no longer true. Integral strings that overflow into floating point numbers will no longer be considered equal.]

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 17-Jun-2011 02:18
If $var not declared.

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

in php 5.3 :
<?php if($var) ?> - dont work and generate error E_NOTICE
php at benizi dot com 15-Feb-2010 10:31
It's interesting to note that 'empty()' and 'boolean : if($x)'
are paired as logical opposites, as are 'is_null()' and 'isset()'.
edgar at goodforall dot eu 15-Dec-2009 06:55
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);
}

?>
info at shaelf dot ru 06-Jan-2008 01:51
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 03:06
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...).
Jan 29-Dec-2005 11:23
Note that php comparison is not transitive:

"php" == 0 => true
0 == null => true
null == "php" => false
jerryschwartz at comfortable dot com 26-Jul-2005 01:04
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 02:27
<?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 07:00
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.