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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)
?>

User Contributed Notes
Booleans
fyrye at torntech dot com
14-Jun-2010 11:39
Since I haven't seen it posted.
Here is a function that you can use if you have a need to force strict boolean values.
Hopefully this will save someone some time from searching for similar.
<?php
function strictBool($val=false){
    return
is_integer($val)?false:$val == 1;
}
?>

Simply put, it verifies that the value passed is (bool)true otherwise it's false.

Examples:
__________________________________
<?php
$myBool
= strictBool(true);
var_dump($myBool);
//returns (bool)true

$myar = array(0 => true);
$myBool = strictBool($myar[0]);
var_dump($myBool);
//returns (bool)true

$myBool = strictBool("hello");
var_dump($myBool);
//returns (bool)false

$myBool = strictBool(false);
var_dump($myBool);
//returns (bool)false

$myBool = strictBool(array(0 => "hello"));
var_dump($myBool);
//returns (bool)false

$myBool = strictBool(1);
var_dump($myBool);
//returns (bool)false

$myBool = strictBool();
var_dump($myBool);
//returns (bool)false
?>
mercusmaximus at yahoo dot com
06-Feb-2010 09:50
Note that the comparison: (false == 0) evaluates to true and so will any value you set to false as well (without casting).
Symbol
11-Apr-2009 08:35
Just a side note, doesn't really matters, the reason -1 is true and not false is because boolean type is treated as unsigned, so -1 would be for example, if it's unsigned int32 translate to hex: 0xFFFFFFFF and back to decimal: 4294967295 which is non-zero. there isn't really a "negative boolean". it's a binary thing. :o (since it used to be a bit and then there was only 0 and 1 as an option)
russell dot harper at springboardnetworks dot com
02-Apr-2009 02:27
PHP is very fussy converting strings to booleans. The only ones it recognizes are '0' or '', everything else evaluates to TRUE, even 'false' and '0.0' are evaluated as true! I suppose this can't be fixed without breaking a lot of existing code.

Example:

<?php

print 'yes'."\t".((bool)'yes'? 1: 0)."\n";
print
'true'."\t".((bool)'true'? 1: 0)."\n";
print
'no'."\t".((bool)'no'? 1: 0)."\n";
print
'false'."\t".((bool)'false'? 1: 0)."\n";
print
'1'."\t".((bool)'1'? 1: 0)."\n";
print
'0'."\t".((bool)'0'? 1: 0)."\n";
print
'0.0'."\t".((bool)'0.0'? 1: 0)."\n";
print
''."\t".((bool)''? 1: 0)."\n";

?>

Output:

yes     1
true    1
no      1
false   1
1       1
0       0
0.0     1
        0
ashafer01 at gmail dot com
26-Feb-2009 03:59
A note when working with PostgreSQL - if you select a boolean field from the database, it returns 't' or 'f'. If you directly evaluate a variable storing a boolean from a PostgreSQL database, it will always return true.

For example...

<?php
$x
= pg_query("SELECT someBool FROM atable");
$x = pg_fetch_array($x);
$x = $x['someBool'];

if (
$x) echo "true";
else echo
"false";
?>

...ALWAYS outputs true
admin at eexit dot fr
04-Nov-2008 08:27
Beware of certain control behavior with boolean and non boolean values :

<?php
// Consider that the 0 could by any parameters including itself
var_dump(0 == 1); // false
var_dump(0 == (bool)'all'); // false
var_dump(0 == 'all'); // TRUE, take care
var_dump(0 === 'all'); // false

// To avoid this behavior, you need to cast your parameter as string like that :
var_dump((string)0 == 'all'); // false
?>
wbcarts at juno dot com
06-Oct-2008 06:59
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.
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.

<?php
$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 04:37
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
*/
?>
terminatorul at gmail dot com
29-Apr-2007 09:21
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.
 

 
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