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。

**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 = 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`

用户评论:

[#1] trexx68 [2015-04-25 17:11:30]

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.

[#2] aravind dot a dot padmanabhan at gmail dot com [2015-04-22 14:31:24]

please note that

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

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

[#3] Anonymous [2014-10-16 18:19:03]

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.

[#4] blue dot hirano at gmail dot com [2014-09-07 02:29:39]

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).

[#5] lorenzo dot campagna at ymail dot com [2014-01-21 21:33:09]

Someone can explain why this comparison result TRUE when it should be FALSE?

<?php $a = "3abcdef"; $b = 3; if($a == $b) {print("Match!");} //Because of this comparison TRUE script will output: ?>

[#6] Anonymous [2013-11-21 13:43:02]

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

[#7] 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.

[#8] php at richardneill dot org [2012-04-12 19:45:28]

[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]

[#9] 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

[#10] 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()'.

[#11] 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( 'eq' => '==', 'ne' => '!=', 'gt' => '>', 'lt' => '<', 'ne2' => '<>', 'lte' => '<=', 'gte' => '>=', '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')); $comp2 = array(); foreach($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); } ?>

[#12] 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 ?>

[#13] 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...).

[#14] Jan [2005-12-29 11:23:21]

Note that php comparison is not transitive:

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

[#15] 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).

[#16] 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.]]

[#17] 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.