Comparison Operators

Comparison operators, as their name implies, allow you to compare two values. You may also be interested in viewing the type comparison tables, as they show examples of various type related comparisons.

Table 15-4. Comparison Operators

Example	Name	Result
$a == $b	Equal	`TRUE` if $a is equal to $b.
$a === $b	Identical	`TRUE` if $a is equal to $b, and they are of the same type. (introduced in PHP 4)
$a != $b	Not equal	`TRUE` if $a is not equal to $b.
$a <> $b	Not equal	`TRUE` if $a is not equal to $b.
$a !== $b	Not identical	`TRUE` if $a is not equal to $b, or they are not of the same type. (introduced in PHP 4)
$a < $b	Less than	`TRUE` if $a is strictly less than $b.
$a > $b	Greater than	`TRUE` if $a is strictly greater than $b.
$a <= $b	Less than or equal to	`TRUE` if $a is less than or equal to $b.
$a >= $b	Greater than or equal to	`TRUE` if $a is greater than or equal to $b.

If you compare an integer with a string, the string is converted to a number. If you compare two numerical strings, they are compared as integers. These rules also apply to the switch statement.


<?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;

}

?>

See also strcasecmp(), strcmp(), Array operators, and the manual section on Types.

Ternary Operator

Another conditional operator is the "?:" (or ternary) operator.
Example 15-2. Assigning a default value

<?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']; } ?>
The expression (expr1) ? (expr2) : (expr3) evaluates to expr2 if expr1 evaluates to TRUE, and expr3 if expr1 evaluates to FALSE.

User Contributed Notes
Comparison Operators

mita at abv dot bg
24-Mar-2005 08:34


Float values comparation:



if ( (string) $a == (string) $b) {

  print 'a is equal to b';

} else {

  print 'a is not equal to b';

}

sven dot heyll at web dot de
05-Dec-2004 03:19


Hi folks,

to the float comparison problem... 



This worked for me:



//! 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 05:47


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 05:35


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
19-Oct-2004 01:05


if you want to use the ?: operator, you should be careful with the precedence.



Here's an example of the priority of operators:



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.



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 06:01


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...



<?



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...



<?



// 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
13-Apr-2004 05:31


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 05:17


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....!!

gphemsley at users dot sourceforge dot net
03-Jan-2004 06:15


For those of you who need to use === with PHP 3, this should do the trick:



<?php



function is_identical( $left, $right )

{

    if( phpversion() >= 4 )

    {

        return ( $left === $right );

    }

    else

    {

        if( ( $left == $right ) && ( gettype( $left ) == gettype( $right ) ) )

        {

            return TRUE;

        }

        else

        {

            return FALSE;

        }

    }

}



?>



1 === '1' is the same as is_identical( 1, '1' ).

jwhiting at hampshire dot edu
09-Dec-2003 05:31


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...

mina86 at tlen dot pl
03-Dec-2003 05:03


I guess quicker method would be:



<?php

$colors = array('#EEEEEE', '#FFFFFF');

while ($i++ < 10) {

?>

    <tr bgColor="<?=$colors[$i%2]?>">

       <td>Cell 1-<?=$i?></td>

       <td>Cell 2-<?=$i?></td>

       <td>Cell 3-<?=$i?></td>

       <td>Cell 4-<?=$i?></td>

   </tr>

<?php } ?>



And you can easily add more colors:



<?php

$colors = array('#EEEEEE', '#FFFFFF', '#DDDDDD', '#CCCCCC');

while ($i++ < 10) {

?>

    <tr bgColor="<?=$colors[$i%4]?>">

       <td>Cell 1-<?=$i?></td>

       <td>Cell 2-<?=$i?></td>

       <td>Cell 3-<?=$i?></td>

       <td>Cell 4-<?=$i?></td>

   </tr>

<?php } ?>

xhenxhe
12-Nov-2003 08:27


This operator is very is usefull and will save you time and lines once you get the hang of it. Try this next time you are looping through rows in a table and want to change the bgColor:



<table border=1 width=100% align=center style="border-collapse: collapse" bgColor="lightblue">

    <tr>

        <td>Column 1</td>

        <td>Column 2</td>

        <td>Column 3</td>

        <td>Column 4</td>

    </tr>

<?

    while ($i++ < 10)

    {

        $rbg = $rbg=="#EEEEEE" ? "#FFFFFF" : "#EEEEEE";

?>

    <tr bgColor="<?=$rbg?>">

        <td>Cell 1-<?=$i?></td>

        <td>Cell 2-<?=$i?></td>

        <td>Cell 3-<?=$i?></td>

        <td>Cell 4-<?=$i?></td>

    </tr>

<?    } ?>

</table>