©
このドキュメントでは、 php中国語ネットマニュアル リリース
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。
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 |
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 |
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 |
[#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.