PHP - Manual: PHP 类型比较表

2024-11-15

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。

注意:
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。

注意:
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。

注意:
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`
`$x = [];`	array	`true`	`false`	`true`	`false`
`$x = ['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`	`[]`	`"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`	`false`*	`false`*
`-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`
`[]`	`false`	`true`	`false`	`false`	`false`	`false`	`false`	`false`	`true`	`true`	`false`	`false`
`"php"`	`true`	`false`	`false`	`false`*	`false`	`false`	`false`	`false`	`false`	`false`	`true`	`false`
`""`	`false`	`true`	`false`	`false`*	`false`	`false`	`false`	`false`	`true`	`false`	`false`	`true`

* 代表在 PHP 8.0.0 之前为 true。

**严格比较 `===`**
	`true`	`false`	`1`	`0`	`-1`	`"1"`	`"0"`	`"-1"`	`null`	`[]`	`"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`
`[]`	`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`

add a note

User Contributed Notes 23 notes

down

php at richardneill dot org ¶

10 years ago


[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]

down

php at benizi dot com ¶

12 years ago


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

down

aidan at php dot net ¶

17 years ago


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.

down

frank ¶

14 years ago


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...).

down

Jan ¶

16 years ago


Note that php comparison is not transitive:

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

down

blue dot hirano at gmail dot com ¶

7 years ago


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).

down

alt dot jl-3gi8b7l at binich dot com ¶

4 years ago


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
?>

down

edgar at goodforall dot eu ¶

12 years ago


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);
}

?>

down

TrickyFoxy ¶

2 years ago


<?php
echo md5('240610708') == md5('QNKCDZO') ? "equal" : "not equal"; // prints equal!!!

down

-1

trexx68 ¶

7 years ago


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.

down

-2

Anonymous ¶

7 years ago


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.

down

-1

jerryschwartz at comfortable dot com ¶

16 years ago


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).

down

-3

crazy888s at hotmail dot com ¶

9 years ago


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.

down

-4

Anonymous ¶

8 years ago


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

down

-2

biziclop at vipmail dot hu ¶

4 years ago


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 ));
}

down

-7

info at shaelf dot ru ¶

14 years ago


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
?>

down

-3

php at ckls dot net ¶

3 years ago


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.

down

-3

mark at theanti dot social ¶

4 years ago


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

down

-12

Jouriy LYSENKO ¶

11 years ago


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

down

-8

aravind dot a dot padmanabhan at gmail dot com ¶

7 years ago


please note that

$x = 0.0 ;
print empty($x); // returns 1 (true) 

$x = "0.0";
print empty($x); // returns blank (false);

down

-10

engineer dot morozov at gmail dot com ¶

6 years ago


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

down

-5

Anonymous ¶

1 year ago


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.

down

-21

tom ¶

17 years ago


<?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.]]

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