PHP: 比较运算符

Last updated: Sun, 25 Nov 2007

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 $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。（PHP 4 引进）
$a != $b	不等	`TRUE`，如果 $a 不等于 $b。
$a <> $b	不等	`TRUE`，如果 $a 不等于 $b。
$a !== $b	非全等	`TRUE`，如果 $a 不等于 $b，或者它们的类型不同。（PHP 4 引进）
$a < $b	小与	`TRUE`，如果 $a 严格小于 $b。
$a > $b	大于	`TRUE`，如果 $a 严格 $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。

如果比较一个整数和字符串，则字符串会被转换为整数。如果比较两个数字字符串，则作为整数比较。此规则也适用于 switch 语句。


<?php
var_dump(0 == "a"); // 0 == 0 -> true
var_dump("1" == "01"); // 1 == 1 -> 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 1 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）
array	任何其它类型	array 总是更大
object	任何其它类型	object 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()，数组运算符和类型一章。

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。

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。

错误控制运算符

位运算符

Last updated: Sun, 25 Nov 2007

add a note User Contributed Notes
比较运算符

crazy888s at hotmail dot com
02-Feb-2010 02:32


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.

ISAWHIM
31-Jan-2010 02:53


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.)

kapoor_rajiv at hotmail dot com
13-Oct-2009 09:09


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>';



?>

pinkgothic at gmail dot com
18-Sep-2009 07:28


"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.

Anonymous
04-Aug-2009 01:44


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.

monkuar at gmail dot com
28-Jul-2009 07:45


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 :(

Anonymous
08-Feb-2009 10:37


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' <?=($gender=='m')?"checked":""?>>Male

<input type='radio' name='gender' value='f' <?=($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.

mruivo at gmail dot com
21-Dec-2008 11:13


Note that an expression where a boolean variable and a string are compared with the equal operator, will always come out true as a string is technically true. For example:



<?php



$variable = true;

if ($variable == "something") {



   //This code will be excecuted



}



?>



To get around this use the identical operator ===, as the types are not the same.

Hayley Watson
27-Oct-2008 12:45


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.

jescribens at urbangolem dot com
05-Apr-2008 01:13


Hi all:



I found this and maybe it can help you, i didn't found it documented anywhere :



Assuming you have a function that returns an array or a null value in failure and you do something like this



<?php

function myfunction()

{

     if($something==$other)

     {

           return array(0=>array(0=>array('valor'=>$other)));

     }else{

           return null;

     }

}



$x = myfunction();



var_dump($x);    //can be null



if($x[0][0]['value'] < 1)

{

    echo "nok";

}else{

    echo "ok";

}



?>



If the function returns null then you get "nok" printed.

As far as I see NULL values are always less than 1, and the fact that I request a sub array ([0][0]['value']) doesn't give me any notice nor warning.



Hope this helps anybody.



Greetings

Amaroq
25-Feb-2008 07:13


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.

ken at smallboxsoftware net
16-Nov-2007 12:20


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.

Hayley Watson
10-Apr-2007 01:38


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.

thomas dot oldbury at tgohome dot com
28-Feb-2007 01:37


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.

fernandoleal at dragoncs dot com
04-Feb-2007 03:19


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;

?>

stepheneliotdewey at gmail [period] com
07-Jan-2007 10:49


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 !==).

04-Jan-2007 11:11


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).

bishop
27-Oct-2006 06:49


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)

pcdinh at phpvietnam dot net
11-Aug-2006 12:50


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.

Alex
17-May-2006 10:49


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).

adam at caucho dot com
09-May-2006 01:49


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...

rshawiii at yahoo dot com
19-Jan-2006 03:36


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


}


?>

sam at liddicott dot com
01-Nov-2005 11:42


Don't be deceived into thinking that === compares objects for identity, it does not. It does a recusrive comparison which fails if there are recusrive object references involved, and will report as identical two different object instances that happen to merely have the same value.


You can see the stated problem at: http://bugs.php.net/bug.php?id=35053





My workaround is php::CompareObjects($a,$b)





<?php


# static class to hold methods to encapsulate php deficiencies in various versions


class php {


  # in === on objects in php4 does a dumb recusrive check instead


  function CompareObject(&$a,&$b) {


    $value='Bah! Stupid===';


    $key="bah".rand(0,1000);


    while(isset($a->$key)) $key.=rand(0,9);





    if (isset($b->$key)) return FALSE;


    $a->$key=$value;


    $result=($a->$key===$b->$key);


    unset($a->$key);


    return $result;


  }


}


?>

08-Sep-2005 04:09


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

sven dot heyll at web dot de
05-Dec-2004 05:19


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 />";


?>

02-Dec-2004 07:47


Concerning floats: It is simply pointless to compare a float with the value "0.3". The number 0.3 is not exactly representable in binary. Period. So is the number 0.1, and an infinite number of others numbers. Just like 1/3 is not exactly representable in decimal. How would you code the test for your float to be one third? Maybe $myFloat == 0.33333333333   Hmm: you see: Everyone would agree that this test is not accurate.



The test $myFloat == 0.3 is making exactly the same mistake.



So the float which you think should be 0.3 is really something very close to it; if you print it in decimal, the conversion will end up with the closest decimal representation, which may well be "0.3". But "0.3" is also the "right display decimal" for hundreds of float values.



The correct way to "compare" floats is: ( $myFloat - 0.3 ) < $EPSILON where $EPSILON is something like 1e-10, depending on your application. Approximate algorithms are the only right way to treat floats, which are only approximate by themselves.

darkcryst at gmail dot com
21-Oct-2004 06:35


be REALLY careful when comparing float values. PHP, like most languages, is vunerable to he problems of floating point precision.



Do NOT compare floats directly, and this also means any decimal value at all.



The headaches finding out if $var = 0.3 caused me are unbelievable. even though the stored variable WAS 0.3 it was still ignoring it - this was to do with the internal float not recognising it as 0.3 even though it *displayed* it as 0.3 when echo'd or printed... basically it was stored imprecisly, but not able to display it as such.



I ended up having to compare after multiplying by 10, rounding, and then dividing by 10... rediculous, but sadly the only way I could find to reliably do it. The round seemed to remove the break in the float...



jesus that took me ages to find...

hiroh2k at yahoo dot com
20-Oct-2004 02:05


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.

jeronimo at DELETE_THIS dot transartmedia dot com
02-Jul-2004 07:01


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





?>

webmaster __AT__ digitalanime __DOT__ nl
14-Apr-2004 06:31


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.

user@example
04-Apr-2004 06:17


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....!!

jwhiting at hampshire dot edu
10-Dec-2003 07:31


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...

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Last updated: Sun, 25 Nov 2007