PHP 8.3.0 RC 6 available for testing

PHP 类型比较表

以下的表格显示了 PHP 类型比较运算符 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 != NANNAN !== 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 25 notes

up
80
php at richardneill dot org
11 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]
up
49
php at benizi dot com
13 years ago
It's interesting to note that 'empty()' and 'boolean : if($x)'
are paired as logical opposites, as are 'is_null()' and 'isset()'.
up
29
aidan at php dot net
18 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.
up
28
frank
16 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...).
up
27
Jan
17 years ago
Note that php comparison is not transitive:

"php" == 0 => true
0 == null => true
null == "php" => false
up
5
TrickyFoxy
3 years ago
<?php
echo md5('240610708') == md5('QNKCDZO') ? "equal" : "not equal"; // prints equal!!!
up
5
alt dot jl-3gi8b7l at binich dot com
5 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
?>
up
8
edgar at goodforall dot eu
13 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);
}

?>
up
5
blue dot hirano at gmail dot com
9 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).
up
3
Anonymous
9 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.
up
1
Jeroen
3 months ago
Be aware of the difference between checking the *value* of an array item, and checking the *existence* of an array item:
<?php
$arr
= [
'x' => 0,
'y' => null,
];

isset(
$arr['x']); // true, same as isset(0)
isset($arr['y']); // false, same as isset(null)

array_key_exists('y', $arr); // true, though the value is null
array_key_exists('z', $arr); // false
up
1
trexx68
8 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.
up
-1
ray dot paseur at SometimesUsesGmail dot com
8 months ago
A colorized version of the loose comparison table is here (no copyright, nor attribution required)
https://iconoun.com/php_type_comparisons.php
up
0
jerryschwartz at comfortable dot com
18 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).
up
-1
php at ckls dot net
5 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.
up
-3
crazy888s at hotmail dot com
10 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.
up
-6
Anonymous
9 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
up
-2
mark at theanti dot social
5 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
up
-2
biziclop at vipmail dot hu
6 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 ));
}
up
-7
info at shaelf dot ru
15 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
?>
up
-8
aravind dot a dot padmanabhan at gmail dot com
8 years ago
please note that

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

$x = "0.0";
print empty($x); // returns blank (false);
up
-14
Jouriy LYSENKO
12 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
up
-4
Anonymous
2 years 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.
up
-10
engineer dot morozov at gmail dot com
7 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 $counter
up
-24
tom
18 years ago
<?php
if (strlen($_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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