文字

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 < $b	小与	`TRUE` ，如果 `$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` 。

如果比较一个数字和字符串或者比较涉及到数字内容的字符串，则字符串会被转换为数值并且比较按照数值来进行。此规则也适用于 switch 语句。当用 === 或 !== 进行比较时则不进行类型转换，因为此时类型和数值都要比对。

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

 switch ( "a" ) {
case  0 :
    echo  "0" ;
    break;
case  "a" :  // never reached because "a" is already matched with 0
     echo  "a" ;
    break;
}
 ?>

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
null 或 string	string	将 `NULL` 转换为 ""，进行数字或词汇比较
bool 或 null	任何其它类型	转换为 bool ， `FALSE` < `TRUE`
object	object	内置类可以定义自己的比较，不同类不能比较，相同类和数组同样方式比较属性（PHP 4 中），PHP 5 有其自己的说明
string ， resource 或 number	string ， resource 或 number	将字符串和资源转换成数字，按普通数学比较
array	array	具有较少成员的数组较小，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

Example #1 标准数组比较代码

  <?php
 // 数组是用标准比较运算符这样比较的
 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  null ;  // uncomparable
         } elseif ( $val  <  $op2 [ $key ]) {
            return - 1 ;
        } elseif ( $val  >  $op2 [ $key ]) {
            return  1 ;
        }
    }
    return  0 ;  // $op1 == $op2
 }
 ?>

参见 strcasecmp() ， strcmp() ，数组运算符和类型章节。

Warning

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是否相等。

更多信息参见 float 。

三元运算符

另一个条件运算符是“?:”（或三元）运算符。

Example #2 赋默认值

  <?php
  // Example usage for: Ternary Operator
  $action  = (empty( $_POST [ 'action' ])) ?  'default'  :  $_POST [ 'action' ];

  // The above is identical to this if/else statement
  if (empty( $_POST [ 'action' ])) {
      $action  =  'default' ;
 } else {
      $action  =  $_POST [ 'action' ];
 }

  ?>

表达式 (expr1) ? (expr2) : (expr3) 在 expr1 求值为 TRUE 时的值为 expr2，在 expr1 求值为 FALSE 时的值为 expr3。

自 PHP 5.3 起，可以省略三元运算符中间那部分。表达式 expr1 ?: expr3 在 expr1 求值为 TRUE 时返回 expr1，否则返回 expr3。

Note: 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。

Note:

建议避免将三元运算符堆积在一起使用。当在一条语句中使用多个三元运算符时会造成 PHP 运算结果不清晰：

Example #3 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'，因为三元运算符是从左往右计算的 // 下面是与上面等价的语句，但更清晰 echo (( true ? 'true' : 'false' ) ? 't' : 'f' ); // here, you can see that the first expression is evaluated to 'true', which // in turn evaluates to (bool)true, thus returning the true branch of the // second ternary expression. ?>

用户评论:

[#1] Hayley Watson [2015-08-24 15:49:47]

When the comparison rules for the spaceship operator say that for "object<=>anything" the object is always greater, and for "array<=>anything" the array is always greater.

The rules should be used in the order they are listed. In the latter case, "anything" means "anything except an object".

The former rule says that "object<=>array" will always decide that the object is greater (and evaluate to a positive integer); to be consistent, the comparison "array<=>object" must also always decide that the object is greater (and evaluate to a negative integer).

[#2] Marcin Kuzawiski [2015-06-21 20:12:37]

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

[#3] gondo [2014-04-25 11:47:54]

beware of the fact, that there is no `<==` nor `>==` therefore `false <= 0` will be `true`. php v. 5.4.27

[#4] sgurukrupa at gmail dot com [2014-04-21 06:23:37]

With respect to using the ternary operator as a 'null-coalescing' operator: expr1 ?: expr2, note that expr1 is evaluated only once.

[#5] Harry Willis [2014-04-18 15:52:13]

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...)

[#6] Boolean_Type [2014-04-08 21:40:00]

Nice and helpful article!)
I would like to ask:

number == null - it converts both types of comparisons to a boolean or numeric type? In the table the author pointed out that to a boolean. But elsewhere I read that to a numeric type.

[#7] mail at mkharitonov dot net [2014-03-21 11:13:05]

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

[#8] damien dot launay dot mail at gmail dot com [2013-06-07 14:46:35]

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.

[#9] bimal at sanjaal dot com [2013-02-25 12:02:35]

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; # 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.

[#10] toader_alexandru at yahoo dot com [2012-07-11 13:56:53]

it looks that

if you check 0 against a string with == then PHP returns true:

php -r 'var_dump(0 == "statuses");'
-> returns TRUE

but not if your string has a number at the beginning:

php -r 'var_dump(0 == "2statuses");'
-> returns FALSE

from the specs I get it that it attempts a conversion - in this case the string to number.

so better use ===
as always :)

[#11] wbcarts at juno dot com [2012-05-17 21:20:19]

COMPARING PHP OBJECTS (compound type)

We have seen that PHP does a lot of type-juggling on its own -- which can wreak havoc in unexpected ways -- but it is still up to us to produce code that is clear, maintainable AND follows the rules we want to follow.

When creating a PHP Object, it is sometimes unclear what makes two of them the same. But the good part is that we can say what is equal and what is not equal. For example, let's say we have a Student class that includes an equals() method which defines what is equal for this type of object.

<?php #Student.php class Student { protected $student_id; protected $student_name; public function __construct($id, $name) { $this->student_id = (int)$id; // cast to integer here $this->student_name = (string)$name; // cast to string here } public function equals(Student $student) { return ($this->getId() == $student->getId()); } public function getId() { return $this->student_id; } public function getName() { return $this->student_name; } public function __toString() { return 'Student [id=' . $this->getId() . ', name=' . $this->getName() . ']'; } } ?>

With this class, the protected variables cannot be tampered with by outside code. Also, the __construct() function casts the variables to the PHP primitives WE WANT, while the equals(Student $student) function, requires an argument of type Student -- which eliminates the need for an IDENTITY '===' check AND prevents any other data types from coming in. One other note: notice how the equals() function only evaluates the $student_id, this allows for two students to have the same name -- which is totally possible.

Here's a short example -- we'll do it correctly AND try to screw it up!

<?php require('Student.php'); $s1 = new Student(122, 'John Doe'); $s2 = new Student(344, 'John Doe'); echo $s1 . '<br>'; // Student [id=122, name=John Doe] echo $s2 . '<br>'; // Student [id=344, name=John Doe] # Check for equality the CORRECT way... echo ($s1->equals($s2) ? 'EQUAL' : 'NOT EQUAL'); // NOT EQUAL # Check for equality by HACKING the known value of $student_id... echo ($s1->equals(122) ? 'EQUAL' : 'NOT EQUAL'); // Catchable fatal error: Argument 1 passed to Student::equals() must be an instance of Student, integer given... etc, etc. ?>

See what I mean by writing code that follows OUR RULES? The Student class does the kind of type-juggling we want (and when we want it done) -- NOT when, where, or why PHP does it (not that there's anything wrong with it).

[#12] Jeremy Swinborne [2012-03-28 20:06:01]

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

[#13] j-a-n at gmx dot de [2011-10-13 02:32:44]

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)

[#14] Cuong Huy To [2011-07-10 07:48:55]

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)

[#15] Mark Simon [2011-06-16 02:20:06]

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;

[#16] email at kleijn dot jp [2011-05-03 07:58:36]

Maybe i am overlooking something but it seems to me that using unset(string) inside a ternary operator creates an error.

(($var1==0 && $var2==0)?unset($var3):$var3=$var1+$var2);

result:
Parse error: syntax error, unexpected T_UNSET

using the traditional form of IF...ELSE works normal.

if($var1==0 && $var2==0) { unset($var3); }
else { $var3=$var1+$var2; }

result:
This unsets var3 or creates a sum of var1+var2 for var3

JP Kleijn
Netherlands

[#17] zak at minion dot net [2011-04-21 11:18:51]

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

[#18] me at lx dot sg [2010-09-23 19:08:12]

Replying to the comment on Aug 6, 2010, the comparisons return TRUE because they are recognized as numerical strings and are converted to integers. If you try "abc" == " abc", it will return FALSE as expected. To avoid the type conversions, simply use the identity operator (===).

[#19] arnaud at arnapou dot net [2010-08-06 01:12:31]

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 !

[#20] mail at markuszeller dot com [2010-08-04 01:40:22]

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

[#21] alan dot g at nospam dot net [2010-05-09 00:44:51]

a function to help settings default values, it returns its own first non-empty argument :

make your own eor combos !

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

[#22] taras dot bogach at gmail dot com [2010-03-31 07:46:06]

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; } } //... } ?>

[#23] crazy888s at hotmail dot com [2010-02-01 22:32:04]

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.

[#24] ISAWHIM [2010-01-30 10:53:34]

When it comes to formatting structure of the conditional statements, I found this to work best and retain logic in views...

<?php $z = 2; $text = ($z===1 ? 'ONE' : ($z===2 ? 'TWO' : ($z===3 ? 'THREE' : 'MORE' ))); echo($text); // RESULT='TWO' // LONGHAND $z = 2; $text = ($z===1?'ONE' : ($z===2?'TWO' : ($z===3?'THREE' : 'MORE'))); echo($text); // RESULT='TWO' ?>

Since this is expected to test logic, and nothing more, only use it to test logic.

To test order, if you ever forget...

<?php $z = 1; $text = ($z===1 ? 'FIRST : OUTTER' : ($z===1 ? 'SECOND : INNER' : ($z===1 ? 'THIRD : LAST' : 'FAIL EVAL DEFAULT' ))); echo($text); // RETURN='FIRST : OUTTER' $z = 2; $text = ($z===1 ? 'FIRST : OUTTER' : ($z===1 ? 'SECOND : INNER' : ($z===1 ? 'THIRD : LAST' : 'FAIL EVAL DEFAULT' ))); echo($text); // RETURN='FAIL EVAL DEFAULT' ?>

(IF ? THEN : ELSE)
(IF ? THEN : ELSE(IF ? THEN : ELSE(IF ? THEN : ELSE))

That can't be read from inside to out, unlike a math formula, because the logic in comparison is not the same. In math nesting, you need the solution to the deepest nested element first. In logic comparison, you always start outside before you compare inside. (Logically, IF there is no door THEN you need something ELSE to get inside. Oh, there is a window... We are inside, now IF there is a fridge THEN open it or ELSE you starve.)

[#25] kapoor_rajiv at hotmail dot com [2009-10-13 06:09:18]

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>'; ?>

[#26] pinkgothic at gmail dot com [2009-09-18 04:28:37]

"Array with fewer members is smaller, if key from operand 1 is not found in operand 2 then arrays are uncomparable, otherwise - compare value by value (see following example)."

The example covers this behaviour, but it isn't immediately obvious, so:

If you're doing loose comparisons in PHP, note that they differ from checking each value individually like $value1==$value2 by adding what amounts to an empty($value1)==empty($value2) check into the mix. I found this out by investigating some (to me) bizarre behaviour.
[Note that the example contains no ==, just > and <. It's its absence that perceivedly 'causes empty() to fire'.]

I was also pleasantly surprised to see PHP recurse. Also clear if you keep in mind that the example implies another function call to itself with > and < if both operands are arrays, but IMO definitely worth stating.

It might also be worth noting that the order of array keys doesn't matter, even if a foreach() would see a 'different' array. Again, covered by the example, but might be worth stressing.

[#27] Anonymous [2009-08-03 22:44:12]

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.

[#28] monkuar at gmail dot com [2009-07-27 16:45:32]

U can even add a variable on that if u wish:

($Profile['skinstyle']=='0')? $lol = "selected":"";

then call it out.. alot faster. if u use EOF.. and such like on ibp :(

[#29] Anonymous [2009-02-07 18:37:20]

Here is some ternary trick I like to use for selecting a default value in a set of radio buttons. This example assumes that a prior value was known and that we are offering a user the chance to edit that prior value. If no prior value was actually known, no default value will be set.

<form>
<input type='radio' name='gender' value='m' <?php=($gender=='m')?"checked":""?>>Male
<input type='radio' name='gender' value='f' <?php=($gender=='f')?"checked":""?>>Female
</form>

When a "=" directly follows a "<?" (no space allowed in between -- the trick does not work with "<?php"), the right side of the operand (here, the result of the ternary operation) is printed out as text into the surrounding HTML code. If using "<?php" form, you will need to do "<?php echo exp1?exp2:exp3 ?>" instead.

[#30] Hayley Watson [2008-10-26 20:45:14]

The cast from null to boolean is documented (on the page describing the boolean type: null->false), and so is the cast from boolean to integer (on the page describing the integer type: false->0), but the cast from null to integer is undefined and the fact that it is currently implemented by casting from null to boolean and then from boolean to integer is explicitly documented (on the page describing the integer type) as something that should not be relied on (so null==0 is true only by accident, but ((int)(bool)null)==0 is true per specification).

Perhaps as well as a "Converting to integer" section on the integer type page there should also be a "Converting from integer" section; similarly for the other types.

[#31] Amaroq [2008-02-25 03:13:33]

Most of the time, you may be content with your conditionals evaluating to true if they are evaluating a non-false, non-zero value. You may also like it when they evaluate to false when you use the number 0.

However, there may be times where you want to make a distinction between a non-false value and a boolean true. You may also wish to make a distinction between a boolean false and a zero.

The identity operator can make this distinction for you.

<?php $a = 'some string'; $b = 123; $c = 0; if($a && $b && (!$c)) { echo "True.\n"; } else { echo "False.\n"; } if($a == true && $b == true && $c == false) { echo "True.\n"; } else { echo "False.\n"; } if($a === true || $b === true || $c === false) { echo "True.\n"; } else { echo "False.\n"; } ?>

The above code outputs the following:
True.
True.
False.

As you can see, in the first two cases, $a and $b are considered true, while $c is considered false. If this wasn't the case, neither of the first two conditionals would have echoed "True."

In the last case, I've cleverly used the || operator to demonstrate that both $a and $b do not evaluate to true with the identity operator, nor does $c evaluate to false.

The === operator can be used to distinguish boolean from non-boolean values.

[#32] ken at smallboxsoftware net [2007-11-15 08:20:36]

This seems a bit odd to me, but PHP can convert two strings into integers during comparison. For example: "700" == "+700" return true even though they are totally different strings.

Use === or strcmp when comparing two strings to ensure that they remain as strings during comparison.

[#33] Hayley Watson [2007-04-09 22:38:42]

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.

[#34] thomas dot oldbury at tgohome dot com [2007-02-27 09:37:23]

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.

[#35] fernandoleal at dragoncs dot com [2007-02-03 11:19:35]

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; ?>

[#36] stepheneliotdewey at gmail [period] com [2007-01-07 06:49:21]

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 !==).

[#37] [2007-01-04 07:11:50]

Since php 5.2 the operator == for object vs object is not recursion safe, it will cause a fatal error if one of the objects contains a refernce to it self (indirect refferences also counts here).
If you are just checking if two object pointers points to the same object use === instead and aviod this issue (you might get a minimal speed bost too).

[#38] bishop [2006-10-26 15:49:53]

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)

[#39] pcdinh at phpvietnam dot net [2006-08-10 09:50:17]

You should be very careful when using == with an result set returned from a query that can be an empty array, multi-dimensional array or a boolean false value (if the query failed to execute). In PHP, an empty array is equivalent to true.

<?php $myArray = array(); // check if there is any error with the query if ($myArray == false) { echo "Yes"; } ?>

return Yes

Use === instead.

[#40] Alex [2006-05-17 07:49:48]

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).

[#41] adam at caucho dot com [2006-05-08 22:49:59]

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...

[#42] rshawiii at yahoo dot com [2006-01-18 11:36:34]

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 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 } ?>

[#43] [2005-09-07 13:09:44]

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

[#44] sven dot heyll at web dot de [2004-12-05 01:19:46]

Hi folks,
to the float comparison problem...

This worked for me:

<?php //! compare two floating point values, return true if they are equal //! (enough) or false otherwise function float_equal($f1, $f2) { return ($f1 > $f2) ? (false) : (!($f1 < $f2)); } // compare floats $f1 = 0.037; $f2 = 1000387.978; echo "$f1 and $f2 are ".(float_equal($f1,$f2)?("equal"):("not equal"))."<br />"; $f1 = 0.3; $f2 = 0.3; echo "$f1 and $f2 are ".(float_equal($f1,$f2)?("equal"):("not equal"))."<br />"; ?>

[#45] hiroh2k at yahoo dot com [2004-10-19 11:05:58]

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.

[#46] jeronimo at DELETE_THIS dot transartmedia dot com [2004-07-02 04:01:12]

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 ?>

[#47] webmaster __AT__ digitalanime __DOT__ nl [2004-04-13 15:31:15]

WARNING!!!!

Let's say, we have this little script:

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

What you want:
If $i is set, display:
Hello, my friend: Me, how are you doing?
If not, display:
Hello, my guest, Guest, please register

BUT, you DON'T get that result!

If $i is set, you get this:
my friend: Me, how are you doing? (so, there's not "Hello, " before it)
If $i is NOT set, you get this:
my friend: Me, how are you doing?

So... That's the same!

You can solve this by using the "(" and ")" to give priority to the ternary operator:

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

When $i is set, you get this:
Hello, my friend: Me, how are you doing? (expected)
When $i is NOT set, you get this:
Hello, my guest, Guest, please register (expected too)

So.. Please, don't be dumb and ALWAYS use the priority-signs (or.. How do you call them?), ( and ).
By using them, you won't get unneeded trouble and always know for sure your code is doing what you want: The right thing.

[#48] user@example [2004-04-04 03:17:24]

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....!!

[#49] jwhiting at hampshire dot edu [2003-12-09 15:31:50]

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...