PHP: Booleans - Manual

Integers

Types

Last updated: Fri, 15 Aug 2008

Booleans

This is the simplest type. A boolean expresses a truth value. It can be either TRUE or FALSE.

Note: The boolean type was introduced in PHP 4.

Syntax

To specify a boolean literal, use the keywords TRUE or FALSE. Both are case-insensitive.


<?php
$foo = True; // assign the value TRUE to $foo
?>

Typically, some kind of operator which returns a boolean value, and the value is passed on to a control structure.


<?php
// == is an operator which test
// equality and returns a boolean
if ($action == "show_version") {
    echo "The version is 1.23";
}

// this is not necessary...
if ($show_separators == TRUE) {
    echo "<hr>\n";
}

// ...because instead, this can be used:
if ($show_separators) {
    echo "<hr>\n";
}
?>

Converting to boolean

To explicitly convert a value to boolean, use the (bool) or (boolean) casts. However, in most cases the cast is unncecessary, since a value will be automatically converted if an operator, function or control structure requires a boolean argument.

See also Type Juggling.

When converting to boolean, the following values are considered FALSE:

the boolean FALSE itself
the integer 0 (zero)
the float 0.0 (zero)
the empty string, and the string "0"
an array with zero elements
an object with zero member variables (PHP 4 only)
the special type NULL (including unset variables)
SimpleXML objects created from empty tags

Every other value is considered TRUE (including any resource).

Warning

-1 is considered TRUE, like any other non-zero (whether negative or positive) number!


<?php
var_dump((bool) "");        // bool(false)
var_dump((bool) 1);         // bool(true)
var_dump((bool) -2);        // bool(true)
var_dump((bool) "foo");     // bool(true)
var_dump((bool) 2.3e5);     // bool(true)
var_dump((bool) array(12)); // bool(true)
var_dump((bool) array());   // bool(false)
var_dump((bool) "false");   // bool(true)
?>

Integers

Types

Last updated: Fri, 15 Aug 2008

add a note User Contributed Notes
Booleans

maykelsb [ta] yahoo [tod] com [tod] br
01-Feb-2008 08:54


At http://www.blueshoes.org/en/developer/syntax_exam/, is available a test where you can try your knowledge about boolean expressions. Hope it helps!

Wackzingo
27-Jan-2008 11:39


It is correct that TRUE or FALSE should not be used as constants for the numbers 0 and 1. But there may be times when it might be helpful to see the value of the Boolean as a 1 or 0. Here's how to do it.



$var1 = TRUE;

$var2 = FALSE;



echo $var1; // Will display the number 1



echo $var2; //Will display nothing



To get it to display the number 0 for a false value you have to typecast it:



echo (int)$var2; //This will display the number 0 for false.

Steve
16-Jan-2008 08:00


PHP does not break any rules with the values of true and false.  The value false is not a constant for the number 0, it is a boolean value that indicates false.  The value true is also not a constant for 1, it is a special boolean value that indicates true.  It just happens to cast to integer 1 when you print it or use it in an expression, but it's not the same as a constant for the integer value 1 and you shouldn't use it as one.  Notice what it says at the top of the page:



A boolean expresses a truth value.



It does not say "a boolean expresses a 0 or 1".



It's true that symbolic constants are specifically designed to always and only reference their constant value.  But booleans are not symbolic constants, they are values.  If you're trying to add 2 boolean values you might have other problems in your application.

Anonymous
07-Jan-2008 12:05


Note that the symbolic constants TRUE and FALSE are treated differently.  I was told that this is a feature, not a bug.



echo false ;

echo (false) ;

echo false+false ;

echo (false+false) ;

echo intval(false) ;

echo '"'.false.'"' ;



echo true ;

echo (true) ;

echo true+true ;

echo (true+true) ;

echo intval(true) ;

echo '"'.true.'"' ;



should produce



00000"0"11221"1"



but instead produces



000""11221"1"



In other words, the only way to output the underlying zero or use it in a string is to use 'false+false' or pass it through intval().  No such tricks are required to get at the 1 that underlies true.



The whole idea of symbolic constants is that the underlying value *always* replaces them during translation, and thus anywhere you would otherwise have to use some obscure "magic number" such as 191, you can use a symbolic constant that makes sense, such as TOTAL_NATIONS.  



Exactly what php gets out of breaking this rule was not explained to me.

artktec at gmail dot com
28-Sep-2007 01:37


Note you can also use the '!' to convert a number to a boolean, as if it was an explicit (bool) cast then NOT.



So you can do something like:



<?php

$t = !0; // This will === true;

$f = !1; // This will === false;

?>



And non-integers are casted as if to bool, then NOT.



Example:



<?php

$a = !array();      // This will === true;

$a = !array('a');   // This will === false;

$s = !"";           // This will === true;

$s = !"hello";      // This will === false;

?>



To cast as if using a (bool) you can NOT the NOT with "!!" (double '!'), then you are casting to the correct (bool).



Example:



<?php

$a = !!array();   // This will === false; (as expected)

/* 

This can be a substitute for count($array) > 0 or !(empty($array)) to check to see if an array is empty or not  (you would use: !!$array).

*/



$status = (!!$array ? 'complete' : 'incomplete');



$s = !!"testing"; // This will === true; (as expected)

/* 

Note: normal casting rules apply so a !!"0" would evaluate to an === false

*/

?>

openspecies
14-Jul-2007 12:22


function is_odd($x) { return ($x & 1); //integer }

function is_even($x) { return (!($x & 1)); //integer }



if(is_even(10) === TRUE) 

  // NO



function is_odd($x) { return (bool) ($x & 1); //boolean }

function is_even($x) { return  (bool) (!($x & 1)); //boolean }



if(is_even(10) === TRUE) 

  // YES



$str = 'Hello World!';



if($str === TRUE) 

  // ecetera



@+

Schraalhans Keukenmeester
24-May-2007 02:03


Re: andy at txtnation dot com

<quote> The braces are of course optional </quote>



Nothing optional about the 'braces'  here.

'(  )' are parentheses. '{  }' are braces. But we get the point.



<?php

$num = 10;

$isEven = !($num % 2);

echo ($isEven) ? 'Even' : 'Odd';

//outputs : Even

$isEven = !$num % 2;

echo ($isEven) ? 'Even' : 'Odd';

//outputs : Odd (with ANY number != 0 !!)

?>



Operator precedence and implicit casts at work:

$num = 10;

!$num       => (implicit cast to bool) $num: (bool) 10 = true

!true       => negate true : false

false % 2   => (implicit cast to int) false : (int) false = 0

0 % 2       => remainder of 0 intdiv 2 : 0

$isEven = 0 => integer assignment : 0

($isEven) ? => (implicit cast to bool) 0 : (bool) 0 = false

echo (false) ? 'Even' : 'Odd' => condition false : 'Odd'



Wether or not PHP actually performs the (bool) casts under the hood is irrelevant to the outcome here.

terminatorul at gmail dot com
30-Apr-2007 06:21


Beware that "0.00" converts to boolean TRUE !



You may get such a string from your database, if you have columns of type DECIMAL or CURRENCY. In such cases you have to explicitly check if the value is != 0 or to explicitly convert the value to int also, not only to boolean.

13-Mar-2007 12:45


Jasper probably meant:

$a = 2; 

$b = 3; 

$aBiggerThanB = $a > $b;

andy at txtnation dot com
26-Feb-2007 02:31


Re: comment from jasper at jtey dot com



It is better to not explicitly test for default values. PHP knows the default values, and so should any programmer worth her/his salt.



Same example rewritten:



<?php

$num = 10;

$isEven = !($num % 2);

?>



The braces are off course optional.

jasper at jtey dot com
06-Jun-2006 04:51


The following expressions are equivalent:


<?php


// setting true


$flag = true;


$flag = True;


$flag = TRUE;


$flag = 1==1;





// setting false


$flag = false;


$flag = False;


$flag = FALSE;


$flag = 1==2;


?>





The moral of the story is that boolean operators return a boolean value, i.e., "1==1" returns a boolean value of true.  Someone who is not aware of this may write a block of code such as:


<?php


// even number?


$num = 10;


if($num % 2 == 0){


  $isEven = true;


}


else{


  $isEven = false;


}


?>





when all that is needed is:


<?php


$num = 10;


$isEven = $num % 2 == 0;


?>





Other examples, for illustrative purposes:


<?php


// two numbers


$a = 2;


$b = 3;


$aBiggerThanB = 2 > 3; // $aBiggerThanB is set to false





// lower case vowel check (corrected)


$c = "u";


$isVowel = $c == "a"|| $c == "e"|| $c == "i"|| $c == "o"|| $c == "u";


?>

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Integers

Types

Last updated: Fri, 15 Aug 2008