比较运算符

比较运算符,如同它们名称所暗示的,允许对两个值进行比较。还可以参考 PHP 类型比较表看不同类型相互比较的例子。

比较运算符
例子 名称 结果
$a == $b 等于 true,如果类型转换后 $a 等于 $b
$a === $b 全等 true,如果 $a 等于 $b,并且它们的类型也相同。
$a != $b 不等 true,如果类型转换后 $a 不等于 $b
$a <> $b 不等 true,如果类型转换后 $a 不等于 $b
$a !== $b 不全等 true,如果 $a 不等于 $b,或者它们的类型不同。
$a < $b 小于 true,如果 $a 严格小于 $b
$a > $b 大于 true,如果 $a 严格大于 $b
$a <= $b 小于等于 true,如果 $a 小于或者等于 $b
$a >= $b 大于等于 true,如果 $a 大于或者等于 $b
$a <=> $b 太空船运算符(组合比较符) $a小于、等于、大于 $b时 分别返回一个小于、等于、大于0的 int 值。

当两个操作对象都是 数字字符串, 或一个是数字另一个是 数字字符串, 就会自动按照数值进行比较。 此规则也适用于 switch 语句。 当比较时用的是 ===!==, 则不会进行类型转换——因为不仅要对比数值,还要对比类型。

警告

PHP 8.0.0 之前,如果 string 与数字或者数字字符串进行比较, 则在比较前会将 string 转化为数字。 在如下示例中会出现不可预料的结果:

<?php
var_dump
(0 == "a");
var_dump("1" == "01");
var_dump("10" == "1e1");
var_dump(100 == "1e2");

switch (
"a") {
case
0:
echo
"0";
break;
case
"a":
echo
"a";
break;
}
?>

以上示例在 PHP 7 中的输出:

bool(true)
bool(true)
bool(true)
bool(true)
0

以上示例在 PHP 8 中的输出:

bool(false)
bool(true)
bool(true)
bool(true)
a

<?php
// 整数
echo 1 <=> 1; // 0
echo 1 <=> 2; // -1
echo 2 <=> 1; // 1

// 浮点数
echo 1.5 <=> 1.5; // 0
echo 1.5 <=> 2.5; // -1
echo 2.5 <=> 1.5; // 1

// 字符串
echo "a" <=> "a"; // 0
echo "a" <=> "b"; // -1
echo "b" <=> "a"; // 1

echo "a" <=> "aa"; // -1
echo "zz" <=> "aa"; // 1

// 数组
echo [] <=> []; // 0
echo [1, 2, 3] <=> [1, 2, 3]; // 0
echo [1, 2, 3] <=> []; // 1
echo [1, 2, 3] <=> [1, 2, 1]; // 1
echo [1, 2, 3] <=> [1, 2, 4]; // -1

// 对象
$a = (object) ["a" => "b"];
$b = (object) ["a" => "b"];
echo
$a <=> $b; // 0

$a = (object) ["a" => "b"];
$b = (object) ["a" => "c"];
echo
$a <=> $b; // -1

$a = (object) ["a" => "c"];
$b = (object) ["a" => "b"];
echo
$a <=> $b; // 1

// 不仅仅比较值,而且也会匹配键
$a = (object) ["a" => "b"];
$b = (object) ["b" => "b"];
echo
$a <=> $b; // 1

?>

对于多种类型,比较运算符根据下表比较(按顺序)。

比较多种类型
运算数 1 类型 运算数 2 类型 结果
nullstring string null 转换为 "",进行数字或词汇比较
boolnull 任何其它类型 转换为 boolfalse < true
object object 内置类可以定义自己的比较,不同类不能比较,相同的类查看对象比较
stringresourceintfloat stringresourceintfloat 将字符串和资源转换成数字,按普通数学比较
array array 成员越少的数组越小,如果运算数 1 中的键不存在于运算数 2 中则数组无法比较,否则挨个值比较(见下例)
object 任何其它类型 object 总是更大
array 任何其它类型 array 总是更大

示例 #1 Boolean/null comparison

<?php
// Bool 和 null 总是作为 bool 比较
var_dump(1 == TRUE); // TRUE - same as (bool)1 == TRUE
var_dump(0 == FALSE); // TRUE - same as (bool)0 == FALSE
var_dump(100 < TRUE); // FALSE - same as (bool)100 < TRUE
var_dump(-10 < FALSE);// FALSE - same as (bool)-10 < FALSE
var_dump(min(-100, -10, NULL, 10, 100)); // NULL - (bool)NULL < (bool)-100 is FALSE < TRUE
?>

示例 #2 标准数组比较代码

<?php
// 数组是用标准比较运算符或者太空船运算符进行比较的
function standard_array_compare($op1, $op2)
{
if (
count($op1) < count($op2)) {
return -
1; // $op1 < $op2
} elseif (count($op1) > count($op2)) {
return
1; // $op1 > $op2
}
foreach (
$op1 as $key => $val) {
if (!
array_key_exists($key, $op2)) {
return
1;
} elseif (
$val < $op2[$key]) {
return -
1;
} elseif (
$val > $op2[$key]) {
return
1;
}
}
return
0; // $op1 == $op2
}
?>

警告

比较浮点数

由于浮点数 float 的内部表达方式,不应比较两个浮点数float是否相等。

更多信息参见 float

注意: 请注意,在比较不同类型的值时,类型转换并不总是很明显,尤其是比较 intbool 或者 intstring。因此,在大多数情况下,通常建议使用 ===!== 进行比较而不是 ==!=

不能比较的值

虽然恒等比较(===!==)可以应用于任意值,其它比较运算符应该仅用于可比较的值。不能比较的值的比较的结果是不确定的,不应依赖。

三元运算符

另一个条件运算符是“?:”(或三元)运算符 。

示例 #3 赋默认值

<?php
// 三元运算符的例子
$action = (empty($_POST['action'])) ? 'default' : $_POST['action'];

// 以上等同于以下的 if/else 语句
if (empty($_POST['action'])) {
$action = 'default';
} else {
$action = $_POST['action'];
}
?>
表达式 (expr1) ? (expr2) : (expr3)expr1 求值为 true 时的值为 expr2,在 expr1 求值为 false 时的值为 expr3

可以省略三元运算符中间那部分。表达式 expr1 ?: expr3 等同于如果 expr1 求值为 true 时返回 expr1 的结果,否则返回 expr3expr1 在这里仅执行一次。

注意: 注意三元运算符是个语句,因此其求值不是变量,而是语句的结果。如果想通过引用返回一个变量这点就很重要。在一个通过引用返回的函数中语句 return $var == 42 ? $a : $b; 将不起作用,以后的 PHP 版本会为此发出一条警告。

注意:

建议避免将三元运算符堆积在一起使用。和其他语言相比, 当在单个表达式中使用多个未加括号的三元运算符时会造成 PHP 运算结果不清晰。 甚至在 PHP 8.0.0 之前,三元运算符是从左到右执行的, 而大多数其他编程语言是从右到左的。 自 PHP 7.4.0 起,弃用依靠左联。 PHP 8.0.0 起,三元运算符是非关联的。

示例 #4 不清晰的三元运算符行为

<?php
// 乍看起来下面的输出是 'true'
echo (true ? 'true' : false ? 't' : 'f');

// 然而,上面语句的实际输出是't',因为在 PHP 8.0.0 之前三元运算符是左联的

// 下面是与上面等价的语句,但更清晰
echo ((true ? 'true' : 'false') ? 't' : 'f');

// 这里可以看到第一个表达式的计算结果是 “true”,第二个表达式的计算结果为 (bool)true,
// 因此返回第二个三元表达式的 true 分支。
?>

注意:

然而,短三元运算符(?:)的链接是稳定且合理的。他将第一个参数进行求值,结果为非假值。注意,未定义的值将会引发警告。

示例 #5 Short-ternary chaining

<?php
echo 0 ?: 1 ?: 2 ?: 3, PHP_EOL; //1
echo 0 ?: 0 ?: 2 ?: 3, PHP_EOL; //2
echo 0 ?: 0 ?: 0 ?: 3, PHP_EOL; //3
?>

NULL 合并运算符

另一个简略运算符是 "??" (NULL 合并)运算符。

示例 #6 设置默认值

<?php
// NULL 合并运算符的例子
$action = $_POST['action'] ?? 'default';

// 以上例子等同于于以下 if/else 语句
if (isset($_POST['action'])) {
$action = $_POST['action'];
} else {
$action = 'default';
}
?>
expr1null,表达式 (expr1) ?? (expr2) 等同于 expr2,否则为 expr1

尤其要注意,当不存在左侧的值时,此运算符也和 isset() 一样不会产生警告。 对于 array 键尤其有用。

注意: 请注意:NULL 合并运算符是一个表达式,产生的也是表达式结果,而不是变量。 返回引用变量时需要强调这一点。 因此,在返回引用的函数里就无法使用这样的语句:return $foo ?? $bar;,还会提示警告。

注意:

null 合并运算符的优先级较低。这意味着如果将它与其它运算符(比如字符串链接或者算术运算符)混合使用,可能需要括号。

<?php
// $name 未定义,引发警告。
print 'Mr. ' . $name ?? 'Anonymous';

// 打印 "Mr. Anonymous"
print 'Mr. ' . ($name ?? 'Anonymous');
?>

注意:

请注意,NULL 合并运算符支持简单的嵌套:

示例 #7 嵌套 NULL 合并运算符

<?php

$foo
= null;
$bar = null;
$baz = 1;
$qux = 2;

echo
$foo ?? $bar ?? $baz ?? $qux; // 输出 1

?>

add a note add a note

User Contributed Notes 45 notes

up
144
crazy888s at hotmail dot com
14 years ago
I couldn't find much info on stacking the new ternary operator, so I ran some tests:

<?php
echo 0 ?: 1 ?: 2 ?: 3; //1
echo 1 ?: 0 ?: 3 ?: 2; //1
echo 2 ?: 1 ?: 0 ?: 3; //2
echo 3 ?: 2 ?: 1 ?: 0; //3

echo 0 ?: 1 ?: 2 ?: 3; //1
echo 0 ?: 0 ?: 2 ?: 3; //2
echo 0 ?: 0 ?: 0 ?: 3; //3
?>

It works just as expected, returning the first non-false value within a group of expressions.
up
88
arnaud at arnapou dot net
13 years ago
[Editor's note: consider using ===]

I discover after 10 years of PHP development something awfull : even if you make a string comparison (both are strings), strings are tested like integers and leading "space" character (even \n, \r, \t) is ignored ....

I spent hours because of leading \n in a string ... it hurts my developper sensibility to see two strings beeing compared like integers and not like strings ... I use strcmp now for string comparison ... so stupid ...

Test code :
<?php

test
("1234", "1234");
test("1234", " 1234");
test("1234", "\n1234");
test("1234", "1234 ");
test("1234", "1234\n");

function
test($v1, $v2) {
    echo
"<h1>[".show_cr($v1)."] vs [".show_cr($v2)."]</h1>";
    echo
my_var_dump($v1)."<br />";
    echo
my_var_dump($v2)."<br />";
    if(
$v1 == $v2) {
        echo
"EQUAL !";
    }
    else {
        echo
"DIFFERENT !";
    }
}

function
show_cr($var) {
    return
str_replace("\n", "\\n", $var);
}

function
my_var_dump($var) {
   
ob_start();
   
var_dump($var);
   
$dump = show_cr(trim(ob_get_contents()));
   
ob_end_clean();
    return
$dump;
}

?>

Displays this ->

[1234] vs [1234]
string(4) "1234"
string(4) "1234"
EQUAL !

[1234] vs [ 1234]
string(4) "1234"
string(5) " 1234"
EQUAL !

[1234] vs [\n1234]
string(4) "1234"
string(5) "\n1234"
EQUAL !

[1234] vs [1234 ]
string(4) "1234"
string(5) "1234 "
DIFFERENT !

[1234] vs [1234\n]
string(4) "1234"
string(5) "1234\n"
DIFFERENT !
up
46
Harry Willis
9 years ago
I was interested about the following two uses of the ternary operator (PHP >= 5.3) for using a "default" value if a variable is not set or evaluates to false:

<?php
(isset($some_variable) && $some_variable) ? $some_variable : 'default_value';

$some_variable ?: 'default_value';
?>

The second is more readable, but will throw an ERR_NOTICE is $some_variable is not set. Of course, this could be overcome by suppressing the notice using the @ operator.

Performance-wise, though, comparing 1 million iterations of the three statements

  (isset($foo) && $foo) ? $foo : ''
  ($foo) ?: ''
  (@$foo) ?: ''

results in the following:

  $foo is NOT SET.
    [isset] 0.18222403526306
    [?:]    0.57496404647827
    [@ ?:]  0.64780592918396
  $foo is NULL.
    [isset] 0.17995285987854
    [?:]    0.15304207801819
    [@ ?:]  0.20394206047058
  $foo is FALSE.
    [isset] 0.19388508796692
    [?:]    0.15359902381897
    [@ ?:]  0.20741701126099
  $foo is TRUE.
    [isset] 0.17265486717224
    [?:]    0.11773896217346
    [@ ?:]  0.16193103790283

In other words, using the long-form ternary operator with isset($some_variable) is preferable overall if $some_variable may not be set.

(error_reporting was set to zero for the benchmark, to avoid printing a million notices...)
up
31
thomas dot oldbury at tgohome dot com
17 years ago
Be careful when using the ternary operator!

The following will not evaluate to the expected result:

<?php
echo "a string that has a " . (true) ? 'true' : 'false' . " condition in. ";
?>

Will print true.

Instead, use this:

<?php
echo "a string that has a " . ((true) ? 'true' : 'false') . " condition in. ";
?>

This will evaluate to the expected result: "a string that has a true condition in. "

I hope this helps.
up
36
jwhiting at hampshire dot edu
20 years ago
note: the behavior below is documented in the appendix K about type comparisons, but since it is somewhat buried i thought i should raise it here for people since it threw me for a loop until i figured it out completely.

just to clarify a tricky point about the == comparison operator when dealing with strings and numbers:

('some string' == 0) returns TRUE

however, ('123' == 0) returns FALSE

also note that ((int) 'some string') returns 0

and ((int) '123') returns 123

the behavior makes senes but you must be careful when comparing strings to numbers, e.g. when you're comparing a request variable which you expect to be numeric. its easy to fall into the trap of:

if ($_GET['myvar']==0) dosomething();

as this will dosomething() even when $_GET['myvar'] is 'some string' and clearly not the value 0

i was getting lazy with my types since php vars are so flexible, so be warned to pay attention to the details...
up
20
jeronimo at DELETE_THIS dot transartmedia dot com
19 years ago
For converted Perl programmers: use strict comparison operators (===, !==) in place of string comparison operators (eq, ne). Don't use the simple equality operators (==, !=), because ($a == $b) will return TRUE in many situations where ($a eq $b) would return FALSE.

For instance...
"mary" == "fred" is FALSE, but
"+010" == "10.0" is TRUE (!)

In the following examples, none of the strings being compared are identical, but because PHP *can* evaluate them as numbers, it does so, and therefore finds them equal...

<?php

echo ("007" == "7" ? "EQUAL" : "not equal");
// Prints: EQUAL

// Surrounding the strings with single quotes (') instead of double
// quotes (") to ensure the contents aren't evaluated, and forcing
// string types has no effect.
echo ( (string)'0001' == (string)'+1.' ? "EQUAL" : "not equal");
// Prints: EQUAL

// Including non-digit characters (like leading spaces, "e", the plus
// or minus sign, period, ...) can still result in this behavior, if
// a string happens to be valid scientific notation.
echo ('  131e-2' == '001.3100' ? "EQUAL" : "not equal");
// Prints: EQUAL

?>

If you're comparing passwords (or anything else for which "near" precision isn't good enough) this confusion could be detrimental. Stick with strict comparisons...

<?php

// Same examples as above, using === instead of ==

echo ("007" === "7" ? "EQUAL" : "not equal");
// Prints: not equal

echo ( (string)'0001' === (string)'+1.' ? "EQUAL" : "not equal");
// Prints: not equal

echo ('  131e-2' === '001.3100' ? "EQUAL" : "not equal");
// Prints: not equal

?>
up
34
mail at mkharitonov dot net
9 years ago
Be careful with the "==" operator when both operands are strings:
<?php
var_dump
('123' == '       123'); // true
var_dump('1e3' == '1000'); // true
var_dump('+74951112233' == '74951112233'); // true
var_dump('00000020' == '0000000000000000020'); // true
var_dump('0X1D' == '29E0'); // true
var_dump('0xafebac' == '11529132'); // true
var_dump('0xafebac' == '0XAFEBAC'); // true
var_dump('0xeb' == '+235e-0'); // true
var_dump('0.235' == '+.235'); // true
var_dump('0.2e-10' == '2.0E-11'); // true
var_dump('61529519452809720693702583126814' == '61529519452809720000000000000000'); // true in php < 5.4.4
up
20
hiroh2k at yahoo dot com
19 years ago
if you want to use the ?: operator, you should be careful with the precedence.

Here's an example of the priority of operators:

<?php
echo 'Hello, ' . isset($i) ? 'my friend: ' . $username . ', how are you doing?' : 'my guest, ' . $guestusername . ', please register';
?>

This make "'Hello, ' . isset($i)" the sentence to evaluate. So, if you think to mix more sentences with the ?: operator, please use always parentheses to force the proper evaluation of the sentence.

<?php
echo 'Hello, ' . (isset($i) ? 'my friend: ' . $username . ', how are you doing?' : 'my guest, ' . $guestusername . ', please register');
?>

for general rule, if you mix ?: with other sentences, always close it with parentheses.
up
39
Anonymous
18 years ago
The following contrasts the trinary operator associativity in PHP and Java.  The first test would work as expected in Java (evaluates left-to-right, associates right-to-left, like if stmnt), the second in PHP (evaluates and associates left-to-right)

<?php

echo "\n\n######----------- trinary operator associativity\n\n";

function
trinaryTest($foo){

   
$bar    = $foo > 20
           
? "greater than 20"
           
: $foo > 10
               
? "greater than 10"
               
: $foo > 5
                   
? "greater than 5"
                   
: "not worthy of consideration";   
    echo
$foo." =>  ".$bar."\n";
}

echo
"----trinaryTest\n\n";
trinaryTest(21);
trinaryTest(11);
trinaryTest(6);
trinaryTest(4);

function
trinaryTestParens($foo){
   
   
$bar    = $foo > 20
           
? "greater than 20"
           
: ($foo > 10
               
? "greater than 10"
               
: ($foo > 5
                   
? "greater than 5"
                   
: "not worthy of consideration"));   
    echo
$foo." =>  ".$bar."\n";
}

echo
"----trinaryTestParens\n\n";
trinaryTestParens(21);
trinaryTestParens(11);
trinaryTest(6);
trinaryTestParens(4);

?>

Output:

######----------- trinary operator associativity

----trinaryTest

21 =>  greater than 5
11 =>  greater than 5
6 =>  greater than 5
4 =>  not worthy of consideration

----trinaryTestParens

21 =>  greater than 20
11 =>  greater than 10
6 =>  greater than 5
4 =>  not worthy of consideration
up
17
kapoor_rajiv at hotmail dot com
14 years ago
A quick way to do mysql bit comparison in php is to use the special character it stores . e.g
<?php
                                       
if ($AvailableRequests['OngoingService'] == '')
                                            echo
'<td>Yes</td>';
                                        else
                                            echo
'<td>No</td>';

?>
up
20
rshawiii at yahoo dot com
18 years ago
You can't just compare two arrays with the === operator
like you would think to find out if they are equal or not.  This is more complicated when you have multi-dimensional arrays.  Here is a recursive comparison function.

<?php
/**
* Compares two arrays to see if they contain the same values.  Returns TRUE or FALSE.
* usefull for determining if a record or block of data was modified (perhaps by user input)
* prior to setting a "date_last_updated" or skipping updating the db in the case of no change.
*
* @param array $a1
* @param array $a2
* @return boolean
*/
function array_compare_recursive($a1, $a2)
{
   if (!(
is_array($a1) and (is_array($a2)))) { return FALSE;}   
   
   if (!
count($a1) == count($a2))
      {
       return
FALSE; // arrays don't have same number of entries
     
}
     
   foreach (
$a1 as $key => $val)
   {
       if (!
array_key_exists($key, $a2))
           {return
FALSE; // uncomparable array keys don't match
             
}
       elseif (
is_array($val) and is_array($a2[$key]))  // if both entries are arrays then compare recursive
          
{if (!array_compare_recursive($val,$a2[$key])) return FALSE;
           }
       elseif (!(
$val === $a2[$key])) // compare entries must be of same type.
          
{return FALSE;
           }
   }
   return
TRUE; // $a1 === $a2
}
?>
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15
Jeremy Swinborne
11 years ago
Beware of the consequences of comparing strings to numbers.  You can disprove the laws of the universe.

echo ('X' == 0 && 'X' == true && 0 == false) ? 'true == false' : 'sanity prevails';

This will output 'true == false'.  This stems from the use of the UNIX function strtod() to convert strings to numbers before comparing.  Since 'X' or any other string without a number in it converts to 0 when compared to a number, 0 == 0 && 'X' == true && 0 == false
up
8
G
6 years ago
Do note, using the ternary operator shorthand (since 5.3), omitting the 2nd expression the first expression will only be called once.

Before 5.3 (or not using the shorthand)
<?php
$val
= f('x') ? f('x') : false;
// f('x') will be run twice
?>

After 5.3
<?php
$val
= f('x') ?: false;
// f('x') will be run once
?>
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18
gondo
9 years ago
beware of the fact, that there is no `<==` nor `>==` therefore `false <= 0` will be `true`. php v. 5.4.27
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16
Alex
17 years ago
I think everybody should read carefully what "jeronimo at DELETE_THIS dot transartmedia dot com" wrote. It's a great pitfall even for seasoned programmers and should be looked upon with a great attention.
For example, comparing passwords with == may result in a very large security hole.

I would add some more to it:

The workaround is to use strcmp() or ===.

Note on ===:

While the php documentation says that, basically,
($a===$b)  is the same as  ($a==$b && gettype($a) == gettype($b)),
this is not true.

The difference between == and === is that === never does any type conversion. So, while, according to documentation, ("+0.1" === ".1") should return true (because both are strings and == returns true), === actually returns false (which is good).
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5
niall at maranelda dot org
6 years ago
Care must be taken when using the spaceship operator with arrays that do not have the same keys:

- Contrary to the notes above ("Example #2 Transcription of standard array comparison"), it does *not* return null if the left-hand array contains a key that the right-hand array does not.
- Because of this, the result depends on the order you do the comparison in.

For example:

<?php
$a
= ['a' => 1, 'b' => 2, 'c' => 3, 'e' => 4];
$b = ['a' => 1, 'b' => 2, 'd' => 3, 'e' => 4];

var_dump($a <=> $b);        // int(1) : $a > $b because $a has the 'c' key and $b doesn't.

var_dump($b <=> $a);        // int(1) : $b > $a because $b has the 'd' key and $a doesn't.
?>
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19
adam at caucho dot com
17 years ago
Note: according to the spec, PHP's comparison operators are not transitive.  For example, the following are all true in PHP5:

"11" < "a" < 2 < "11"

As a result, the outcome of sorting an array depends on the order the elements appear in the pre-sort array.  The following code will dump out two arrays with *different* orderings:

<?php
$a
= array(2,    "a""11", 2);
$b = array(2,    "11", "a"2);
sort($a);
var_dump($a);
sort($b);
var_dump($b);
?>

This is not a bug report -- given the spec on this documentation page, what PHP does is "correct".  But that may not be what was intended...
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13
bishop
17 years ago
When you want to know if two arrays contain the same values, regardless of the values' order, you cannot use "==" or "===".  In other words:

<?php
(array(1,2) == array(2,1)) === false;
?>

To answer that question, use:

<?php
function array_equal($a, $b) {
    return (
is_array($a) && is_array($b) && array_diff($a, $b) === array_diff($b, $a));
}
?>

A related, but more strict problem, is if you need to ensure that two arrays contain the same key=>value pairs, regardless of the order of the pairs.  In that case, use:

<?php
function array_identical($a, $b) {
    return (
is_array($a) && is_array($b) && array_diff_assoc($a, $b) === array_diff_assoc($b, $a));
}
?>

Example:
<?php
$a
= array (2, 1);
$b = array (1, 2);
// true === array_equal($a, $b);
// false === array_identical($a, $b);

$a = array ('a' => 2, 'b' => 1);
$b = array ('b' => 1, 'a' => 2);
// true === array_identical($a, $b)
// true === array_equal($a, $b)
?>

(See also the solution "rshawiii at yahoo dot com" posted)
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13
Cuong Huy To
12 years ago
In the table "Comparison with Various Types", please move the last line about "Object" to be above the line about "Array", since Object is considered to be greater than Array (tested on 5.3.3)

(Please remove my "Anonymous" post of the same content before. You could check IP to see that I forgot to type my name)
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17
stepheneliotdewey at gmail [period] com
17 years ago
Note that typecasting will NOT prevent the default behavior for converting two numeric strings to numbers when comparing them.

e.g.:

<?php
if ((string) '0123' == (string) '123')
    print
'equals';
else
    print
'doesn\'t equal';
?>

Still prints 'equals'

As far as I can tell the only way to avoid this is to use the identity comparison operators (=== and !==).
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1
itsacon at itsacon dot net
3 years ago
Be aware that the null coalesce operator (??) has a lower priority than most other operators, so parentheses are usually a good idea if the output is used in anything other than an assignment.

<?php
$var
= 1;
if (
$var ?? 0 == 2) {}  // will evaluate to true

if (2 == $undefinedVar ?? 0) {}  // will throw an error

if (($var ?? 0) == 2) {}  // will evaluate to false
?>

https://www.php.net/manual/en/language.operators.precedence.php
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4
prezire at gmail dot com
8 years ago
Take note when grouping ternary operations that return either boolean or integer concatenated to a string:
<?php
 
echo 'hello ' . true ? 1 : 0, //Outputs 1
      
'hello ' . (true ? 1 : 0); //Outputs hello 1
?>
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1
Sumon Mahmud
4 years ago
Extending from here: https://www.php.net/manual/en/language.operators.comparison.php#121907

$a = ['a' => 1, 'b' => 2, 'c' => 3, 'e' => 4];
$b = ['a' => 1, 'b' => 2, 'd' => 3, 'e' => 4];

echo $a > $b; // 0
echo $b > $a; // 0
echo $a <$b; // 0
echo $b < $a; // 0

If using spaceship operator then it is returning true like :

echo $a <=> $b; //1
echo $b <=> $a; //1
echo $a <=> $b; //1
echo $b <=> $a; //1
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13
Anonymous
14 years ago
Note: The ternary shortcut currently seems to be of no use in dealing with unexisting keys in an array, as PHP will throw an error. Take the following example.

<?php
$_POST
['Unexisting'] = $_POST['Unexisting'] ?: false;
?>

PHP will throw an error that the "Unexisting" key does not exist. The @ operator does not work here to suppress this error.
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11
bimal at sanjaal dot com
11 years ago
I came across peculiar outputs while I was attempting to debug a script

<?php
# Setup platform (pre conditions somewhere in a loop)
$index=1;
$tally = array();

# May work with warnings that $tally[$index] is not initialized
# Notice: Undefined offset: 1 in D:\htdocs\colors\ColorCompare\i.php on line #__
# It is an old fashioned way.
# $tally[$index] = $tally[$index] + 1;

# Does not work: Loops to attempt to change $index and values are aways unaffected
$tally[$index] = isset($tally[$index])?$tally[$index]:0+1;
$tally[$index] = isset($tally[$index])?$tally[$index]:0+1;
$tally[$index] = isset($tally[$index])?$tally[$index]:0+1;
/*
# These three lines output:
Array
(
    [1] => 1
)
*/

# Works: This is what I need/expect
# $tally[$index] = 1+(isset($tally[$index])?$tally[$index]:0);

print_r($tally);
?>

The second block obviously does not work what one expects.
Third part is good.
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9
alan dot g at nospam dot net
13 years ago
a function to help settings default values, it returns its own first non-empty argument :

make your own eor combos !

<?php

/*
* Either Or
*
* usage:  $foo = eor(test1(),test2(),"default");
* usage:  $foo = eor($_GET['foo'], foogen(), $foo, "bar");
*/

function eor() {
   
$vars = func_get_args();
     while (!empty(
$vars) && empty($defval))   
        
$defval = array_shift($vars);         
     return
$defval;
}



?>
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10
Hayley Watson
16 years ago
Note that the "ternary operator" is better described as the "conditional operator". The former name merely notes that it has three arguments without saying anything about what it does. Needless to say, if PHP picked up any more ternary operators, this will be a problem.

"Conditional Operator" is actually descriptive of the semantics, and is the name historically given to it in, e.g., C.
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13
fernandoleal at dragoncs dot com
17 years ago
If you need nested ifs on I var its important to group the if so it works.
Example:
<?php
//Dont Works
//Parse error: parse error, unexpected ':'
$var='<option value="1" '.$status == "1" ? 'selected="selected"' :''.'>Value 1</option>';
//Works:
$var='<option value="1" '.($status == "1" ? 'selected="selected"' :'').'>Value 1</option>';

echo
$var;
?>
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7
Mark Simon
12 years ago
The use of 5.3’s shortened ternary operator allows PHP to coalesce a null or empty value to an alternative:

$value = $planA ?: $planB;

My own server doesn’t yet run 5.3. A nice alternative is to use the “or” operator:

$value = $planA or $value = planB;
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4
Marcin Kuzawiski
8 years ago
A < B and still B < A...

$A = [1 => 1, 2 => 0, 3 => 1];
$B = [1 => 1, 3 => 0, 2 => 1];

var_dump($A < $B);  // TRUE
var_dump($B < $A);  // TRUE

var_dump($A > $B);  // TRUE
var_dump($B > $A);  // TRUE

Next - C and D are comparable, but neither C < D nor D < C (and still C != D)...

$C = [1 => 1, 2 => 1, 3 => 0];
$D = [1 => 1, 3 => 1, 2 => 0];

var_dump($C < $D); // FALSE
var_dump($D < $C); // FALSE

var_dump($C > $D); // FALSE
var_dump($D > $C); // FALSE

var_dump($D == $C); // FALSE
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3
Romain
5 years ago
?? vs isset() with __isset() and __get()

<?php

class A
{
    public function
__get($id)
    {
        return
'a value';
    }
}

class
B
{
    public function
__isset($id)
    {
        return
false;
    }
   
    public function
__get($id)
    {
        return
'a value';
    }
}

class
c
{
    protected
$test = "a value";
   
    public function
__isset($id)
    {
        return
true;
    }
}

$a = new A();
$b = new B();
$c = new C();

echo isset(
$a->test) ? $a->test : 'nothing'; // "nothing"
echo $a->test ?? 'nothing'; // "a value", isset() is not called!

echo isset($b->test) ? $b->test : 'nothing'; // "nothing"
echo $b->test ?? 'nothing'; // "nothing", __isset() is called

echo isset($c->test) ? $c->test : 'nothing'; // throw an Exception
echo $c->test ?? 'nothing'; // "nothing"

?>
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2
azz
4 years ago
Keep in mind that ?: operator is NOT fully equal to empty()

?: can't check non-existent array index (as describe here https://www.php.net/manual/ru/language.operators.comparison.php#92685) and vars

Check this:

<?php
ini_set
('error_reporting', E_ALL);

$t = [];

var_dump(!isset($t['z']) || $t['z'] == FALSE); // true, this that empty() do
var_dump(empty($t['z'])); // true
var_dump(isset($t['z'])); // false

$v1 = $t['z'] ?: false; // Notice:  Undefined index: z
$v2 = $t['z'] ?? false; // silent!

var_dump($v1); // false
var_dump($v2); // false

var_dump(!isset($non_existent_var) || $non_existent_var == FALSE); // true, this that empty() do
var_dump(empty($non_existent_var)); // true
var_dump(isset($non_existent_var)); // false

$v1 = $non_existent_var ?: false; // Notice:  Undefined variable: non_existent_var
$v2 = $non_existent_var ?? false; // silent!

var_dump($v1); // false
var_dump($v2); // false
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6
j-a-n at gmx dot de
12 years ago
Please be careful when comparing strings with floats, especally when you are using the , as decimal.

<?php
var_dump
($alt);
var_dump($neu);
var_dump($alt == $neu);
?>

string(9) "590217,73"
float(590217,73)
bool(false)

not the float is cast to a string and then string-compared, but the string is cast to a float and then float-compared.

to compare as strings use strval!

<?php
var_dump
(strval($alt));
var_dump(strval($neu));
var_dump(strval($alt) == strval($neu));
?>

string(9) "590217,73"
string(9) "590217,73"
bool(true)
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8
user@example
19 years ago
With Nested ternary Operators you have to set the logical  parentheses to get the correct result.

<?php
$test
=true;
$test2=true;

(
$test) ? "TEST1 true" :  ($test2) ? "TEST2 true" : "false";
?>
This will output: TEST2 true;

correct:

<?php
$test
=true;
$test2=true;

(
$test) ? "TEST1 true" : (($test2) ? "TEST2 true" : "false");
?>

Anyway don't nest them to much....!!
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2
Ryan Mott
4 years ago
Searching for "double question mark" operator should find this page (and hopefully after this comment the crawlers will agree)
up
2
sgurukrupa at gmail dot com
9 years ago
With respect to using the ternary operator as a 'null-coalescing' operator: expr1 ?: expr2, note that expr1 is evaluated only once.
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5
zak at minion dot net
12 years ago
be careful when trying to concatenate the result of a ternary operator to a string

<?php
print '<div>'.(FALSE) ? 'TRUE [bad ternary]' : 'FALSE [bad ternary]';
print
'<br><br>';
print
'<div>'.((FALSE) ? 'TRUE [good ternary]' : 'FALSE [good ternary]');
?>

yields:

TRUE [bad ternary]

FALSE [good ternary]

this is because the ternary evaluates '<div>'.(FALSE) not (FALSE) - so the end result is TRUE
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4
taras dot bogach at gmail dot com
13 years ago
Boolean switch usege

<?php
class User_Exception extends Exception{}
class
User{
  public function
register($login,$pass,$passCheck)
    switch(
false){
      case(
strlen($pass) >= 5):
        throw new
User_Exception("Password must be at last 5 chars length");
      case(
$pass == $passCheck):
        throw new
User_Exception("Password is not confirmed!");
      case(
strlen($login) >= 5):
        throw new
User_Exception("Login must be at last 5 chars length");
     
//Do other checks
     
default:
       
//Do registration
       
return true;
    }
  }
 
//...
}
?>
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1
damien dot launay dot mail at gmail dot com
10 years ago
I found a nice way to use of new "?:" operator:

$a = array();
$a['foo'] = 'oof';

$b = @ ($a['foo'] ?: 'No foo');
$c = @ ($a['bar'] ?: 'No bar');

var_dump($b, $c);

Output:

string(3) "oof"
string(6) "No bar"

No error is thrown and $c is set with correct value.

Benefit: no need to use isset.
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1
halfhearted13 at gmail dot com
3 years ago
Both Null Coalescing ( ?? ) and Ternary ( ? : ) can work at a time.

<?php

$a
= "user name";
echo
$a = null ?? $a ? "sb" : "not found"; // it prints : sb
//as null coalescing has null on left it goes to 2nd expr $a. $a is defined so //output will be the 1st expr of Ternay operator.
?>

<?php

echo $x = "" ?? "" ? : "not found"; // it prints:  not found.
// null coalescing has empty value of its left. so it prints right expr which is //also empty. so the output will be the 2nd expr of ternary(written in short)

?>

<?php
echo $x = "" ?? "" ?? "" ? : false// prints nothing.
// if you add var_dump() you see bool(false)
?>
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0
yiminrong at yahoo dot ca
3 years ago
The string equality operator has a big gotcha in that if both operators match the format /^0+[Ee][0-9]+$/, then the values will be considered equal. All these, which represent common use cases, will output true:

echo '0e56' == '0E31'; // comparing short hex strings
echo md5('240610708') == md5('QNKCDZO'); // comparing hashes - see comment by Ray Paseur in md5 function
echo '000e123' == '00e0123'; // permutation of a string

The reason is that strings in the format /^0+[Ee][0-9]+$/ are interpreted as a number in scientific notation and zero raised to any power is zero.

Unless it is certain that the string will not match the specific format, then === should be used instead of == for strings.
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-1
Tahazzot
2 years ago
Very careful when reading PHP documentation, Here's a lot of miss information.

According to documentation, They say's (int) 0 == (string) "a" is true. But it is not in PHP 8.

var_dump(0 == "a"); // 0 == 0 -> true

Now In PHP 8 it's False.
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-1
Ireneusz Pachulski
3 years ago
Note that spaceship operator (<=>) is binary safe.

<?php
$a
= "Hello";
$b = "Hello\x00World";

echo (
$a <=> $b) . "<br>"; // -1
echo strcmp($a, $b) . "<br>"; // -6
echo strcoll($a, $b) . "<br>"; // 0 => not binary safe
?>
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-2
instatiendaweb at gmail dot com
3 years ago
switch ("a") {
case 0:
    echo "0";
    break;
case "a": // nunca alcanzado debido a que "a" ya ha coincidido con 0
    echo "a";
    break;
}
In php 8.0 is echo "a";
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-1
mail at markuszeller dot com
13 years ago
I prefer writing (!$a == 'hello') much more than ($a != 'hello'), but I wondered about the performance.

So I did a benchmark:
<?php
for($bench = 0; $bench < 3; $bench++)
{
   
$start = microtime(true);
   
$a = 1;
    for(
$i = 0; $i < 100000000; $i++)
  {
        if(!
$a == 'hello') $b++;
    }
   
$end = microtime(true);
    echo
"Used time: " . ($end-$start) . "\n";
}
?>
and it results with

# if($a != 'hello')
Used time: 12.552895069122
Used time: 12.548940896988
Used time: 12.470285177231

# if(!$a == 'hello')
Used time: 7.6532161235809
Used time: 7.6426539421082
Used time: 7.6452689170837
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