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PHP : Language Reference : Types : Booleans

Booleans

This is the easiest 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 either the keyword TRUE or FALSE. Both are case-insensitive.

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

Usually you use some kind of operator which returns a boolean value, and then pass it on to a control structure.

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<?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 you can simply type
if ($show_separators) {
   echo "<hr>\n";
}
?>

Converting to boolean

To explicitly convert a value to boolean, use either the (bool) or the (boolean) cast. However, in most cases you do not need to use the cast, 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!

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<?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)
?>

Related Examples ( Source code ) » language.types.boolean

Examples ( Source code ) » PHP provides a couple of constants especially for use as Booleans

Code Examples / Notes » language.types.boolean

jasper
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";
?>

andy
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.

schraalhans keukenmeester
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.

artktec
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
*/
?>

12-mar-2007 03:45
Jasper probably meant:
$a = 2;
$b = 3;
$aBiggerThanB = $a > $b;

openspecies
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
@+

terminatorul
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.

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Introduction
Booleans
Integers
Floating point numbers
Strings
Arrays
Objects
Resource
NULL
Pseudo-types and variables used in this documentation
Type Juggling
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