PHP 8.4.0 RC2 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 8 notes

up
55
php at benizi dot com
14 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
25
Jan
18 years ago
Note that php comparison is not transitive:

"php" == 0 => true
0 == null => true
null == "php" => false
up
24
frank
17 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
2
Jeroen
1 year 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
10
edgar at goodforall dot eu
14 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
7
blue dot hirano at gmail dot com
10 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
jerryschwartz at comfortable dot com
19 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
mark at theanti dot social
6 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
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