PHP: Booleans - Manual

Last updated: Fri, 10 Oct 2008

Booleans

Dies ist der einfachste Typ. Ein boolean Ausdruck ist ein Wahrheitswert der entweder TRUE (wahr) oder FALSE (falsch) sein kann.

Hinweis: Der boolean Typ wurde in PHP 4 eingeführt.

Syntax

Ein boolean Wert wird über die Schlüsselworte TRUE und FALSE spezifiziert, Groß- und Kleinschreibung ist dabei nicht von Bedeutung.


<?php
$foo = True; // weist $foo den Wert TRUE zu
?>

Normalerweise wird ein boolean von einem Operator zurückgegeben und an eine Kontrollstruktur weitergegeben.


<?php
// == ist ein Operator der auf Gleichheit prüft
// und ein boolean Ergebnis zurückgibt
if ($action == "show_version") {
    echo "Die Version ist 1.23";
}

// die Angabe von '== TRUE' ist hier nicht nötig
if ($show_separators == TRUE) {
    echo "<hr>\n";
}

// ... stattdessen funktioniert auch einfach das folgende:
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.

Siehe auch Typumwandlungen.

Bei der Konvertierung zum Typ boolean gelten die folgenden Werte als FALSE:

boolean FALSE selbst
integer 0 (zero)
float 0.0 (zero)
Der leere string, und der string "0"
Ein array ohne Elemente
Ein object ohne Eigenschaftsvariablen (nur PHP 4)
Der spezielle Typ NULL (inklusive nicht gesetzter Variablen)
SimpleXML Objekte die aus leeren Tags erzeugt wurden.

Jeder andere Wert wird als TRUE angenommen (inklusive jeglicher resource Werte).

Warnung

-1 gilt als TRUE wie jeder andere Integerwert ungleich 0 (egal ob positiv oder negativ)!


<?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

Typen

Last updated: Fri, 10 Oct 2008

add a note User Contributed Notes
Booleans

wbcarts at juno dot com
06-Oct-2008 07:59


CODING PRACTICE...



Much of the confusion about booleans (but not limited to booleans) is the fact that PHP itself automatically makes a type cast or conversion for you, which may NOT be what you want or expect. In most cases, it's better to provide functions that give your program the exact behavior you want.

<?php



function boolNumber($bValue = false) {                      // returns integer

  return ($bValue ? 1 : 0);

}



function boolString($bValue = false) {                      // returns string

  return ($bValue ? 'true' : 'false');

}



$a = true;                                                  // boolean value

echo 'boolean $a AS string = ' . boolString($a) . '<br>';   // boolean as a string

echo 'boolean $a AS number = ' . boolNumber($a) . '<br>';   // boolean as a number

echo '<br>';



$b = (45 > 90);                                             // boolean value

echo 'boolean $b AS string = ' . boolString($b) . '<br>';   // boolean as a string

echo 'boolean $b AS number = ' . boolNumber($b) . '<br>';   // boolean as a number

echo '<br>';



$c = boolNumber(10 > 8) + boolNumber(!(5 > 10));            // adding booleans

echo 'integer $c = ' . $c .'<br>';



?>

Results in the following being printed...



 boolean $a AS string = true

 boolean $a AS number = 1



 boolean $b AS string = false

 boolean $b AS number = 0



 integer $c = 2



In other words, if we know what we want out of our program, we can create functions to accommodate. Here, we just wanted 'manual control' over numbers and strings, so that PHP doesn't confuse us.

maykelsb [ta] yahoo [tod] com [tod] br
31-Jan-2008 11:54


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 02:39


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
15-Jan-2008 11:00


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
06-Jan-2008 03:05


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
27-Sep-2007 05:37


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
13-Jul-2007 04:22


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
23-May-2007 06:03


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
29-Apr-2007 10:21


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.

12-Mar-2007 03:45


Jasper probably meant:

$a = 2; 

$b = 3; 

$aBiggerThanB = $a > $b;

andy at txtnation dot com
25-Feb-2007 05:31


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
05-Jun-2006 08:51


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";


?>

add a note

Integers

Typen

Last updated: Fri, 10 Oct 2008