Tipos
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!
Booleanos
Este es el tipo más simple. Un boolean expresa un valor de verdad. Puede ser TRUE or FALSE.
Note: El tipo booleano fue introducido en PHP 4.
Sintaxis
Para especificar un literal booleano, use alguna de las palabras clave TRUE o FALSE. Ambas son insensibles a mayúsculas y minúsculas.
<?php
$foo = True; // asignar el valor TRUE a $foo
?>
Usualmente se usa algún tipo de operador que deuelve un valor boolean, y luego éste es pasado a una estructura de control.
<?php
// == es un operador que prueba por
// igualdad y devuelve un booleano
if ($accion == "mostrar_version") {
echo "La versión es 1.23";
}
// esto no es necesario...
if ($mostrar_separadores == TRUE) {
echo "<hr>\n";
}
// ...porque se puede escribir simplemente
if ($mostrar_separadores) {
echo "<hr>\n";
}
?>
Conversión a booleano
Para convertir explícitamente un valor a boolean, use el moldeamiento (bool) o (boolean). Sin embargo, en la mayoría de casos no es necesario usar el moldeamiento, ya que un valor será convertido automáticamente si un operador, función o estructura de control requiere un argumento tipo boolean.
Vea también Manipulación de Tipos.
Cuando se realizan conversiones a boolean, los siguientes valores son considerados FALSE:
- el boolean FALSE mismo
- el integer 0 (cero)
- el float 0.0 (cero)
- el valor string vacío, y el string "0"
- un array con cero elementos
- un object con cero variables miembro (sólo en PHP 4)
- el tipo especial NULL (incluyendo variables no definidas)
- objetos SimpleXML creados desde etiquetas vacías
Warning
¡-1 es considerado TRUE, como cualquier otro número diferente a cero (ya sea negativo o positivo)!
<?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 NotesBooleanos
maykelsb [ta] yahoo [tod] com [tod] br
01-Feb-2008 12:54
01-Feb-2008 12:54
Wackzingo
27-Jan-2008 03:39
27-Jan-2008 03:39
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 12:00
16-Jan-2008 12:00
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 04:05
06-Jan-2008 04:05
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 06:37
27-Sep-2007 06:37
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');
$s = !!"testing"; // This will === true; (as expected)
/*
Note: normal casting rules apply so a !!"0" would evaluate to an === false
*/
?>
openspecies
13-Jul-2007 05:22
13-Jul-2007 05:22
function is_odd($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 07:03
23-May-2007 07:03
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 11:21
29-Apr-2007 11:21
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 04:45
Jasper probably meant:
$a = 2;
$b = 3;
$aBiggerThanB = $a > $b;
andy at txtnation dot com
25-Feb-2007 06:31
25-Feb-2007 06:31
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 09:51
05-Jun-2006 09:51
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";
?>