Types
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.
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)
?>
add a note
User Contributed NotesBooleans
wbcarts at juno dot com
07-Oct-2008 02:59
07-Oct-2008 02:59
maykelsb [ta] yahoo [tod] com [tod] br
01-Feb-2008 07:54
01-Feb-2008 07:54
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 10:39
27-Jan-2008 10:39
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 07:00
16-Jan-2008 07:00
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 11:05
06-Jan-2008 11:05
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 12:37
28-Sep-2007 12:37
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');
$s = !!"testing"; // This will === true; (as expected)
/*
Note: normal casting rules apply so a !!"0" would evaluate to an === false
*/
?>
openspecies
13-Jul-2007 11:22
13-Jul-2007 11:22
function is_odd($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 01:03
24-May-2007 01:03
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 05:21
30-Apr-2007 05:21
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 11:45
Jasper probably meant:
$a = 2;
$b = 3;
$aBiggerThanB = $a > $b;
andy at txtnation dot com
26-Feb-2007 01:31
26-Feb-2007 01:31
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 03:51
06-Jun-2006 03:51
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";
?>