Булев
Это простейший тип. boolean выражает истинность значения. Он может быть либо TRUE , либо FALSE .
Синтаксис
Для указания boolean , используйте константы TRUE или FALSE . Обе они регистронезависимы.
Обычно, некоторый оператор возвращает boolean значение, которое потом передается управляющей конструкции.
// == это оператор, который проверяет
// эквивалентность и возвращает boolean
if ( $action == «show_version» ) echo «The version is 1.23» ;
>
// это необязательно.
if ( $show_separators == TRUE ) echo «
\n» ;
>
// . потому что следующее имеет тот же самый смысл:
if ( $show_separators ) echo «
\n» ;
>
?>
Преобразование в булев тип
Для явного преобразования в boolean , используйте (bool) или (boolean). Однако, в большинстве случаев приведение типа необязательно, так как значение будет автоматически преобразовано, если оператор, функция или управляющая конструкция требует boolean аргумент.
При преобразовании в boolean , следующие значения рассматриваются как FALSE :
- само значение booleanFALSE
- integer 0 (ноль)
- float 0.0 (ноль)
- пустая строка, и строка «0»
- массив без элементов
- объект без полей (только для PHP 4)
- особый тип NULL (включая неустановленные переменные)
- Объекты SimpleXML, созданные из пустых тегов
Все остальные значения рассматриваются как TRUE (включая любой resource).
-1 рассматривается как TRUE , как и любое другое ненулевое (отрицательное или положительное) число!
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)
?>
boolval
echo ‘0: ‘ .( boolval ( 0 ) ? ‘true’ : ‘false’ ). «\n» ;
echo ’42: ‘ .( boolval ( 42 ) ? ‘true’ : ‘false’ ). «\n» ;
echo ‘0.0: ‘ .( boolval ( 0.0 ) ? ‘true’ : ‘false’ ). «\n» ;
echo ‘4.2: ‘ .( boolval ( 4.2 ) ? ‘true’ : ‘false’ ). «\n» ;
echo ‘»»: ‘ .( boolval ( «» ) ? ‘true’ : ‘false’ ). «\n» ;
echo ‘»string»: ‘ .( boolval ( «string» ) ? ‘true’ : ‘false’ ). «\n» ;
echo ‘»0″: ‘ .( boolval ( «0» ) ? ‘true’ : ‘false’ ). «\n» ;
echo ‘»1″: ‘ .( boolval ( «1» ) ? ‘true’ : ‘false’ ). «\n» ;
echo ‘[1, 2]: ‘ .( boolval ([ 1 , 2 ]) ? ‘true’ : ‘false’ ). «\n» ;
echo ‘[]: ‘ .( boolval ([]) ? ‘true’ : ‘false’ ). «\n» ;
echo ‘stdClass: ‘ .( boolval (new stdClass ) ? ‘true’ : ‘false’ ). «\n» ;
?>
The above example will output:
0: false 42: true 0.0: false 4.2: true "": false "string": true "0": false "1": true [1, 2]: true []: false stdClass: true
See Also
- floatval() — Get float value of a variable
- intval() — Get the integer value of a variable
- strval() — Get string value of a variable
- settype() — Set the type of a variable
- is_bool() — Finds out whether a variable is a boolean
- Type juggling
User Contributed Notes 8 notes
To anyone like me who came here looking for a way to turn any value into a 0/1 that will fit into a MySQL boolean (tinyint) field:
$tinyint = (int) filter_var ( $valToCheck , FILTER_VALIDATE_BOOLEAN );
?>
tinyint will be 0 (zero) for values like string «false», boolean false, int 0
tinyint will be 1 for values like string «true», boolean true, int 1
Useful if you are accepting data that might be from a language like Javascript that sends string «false» for a boolean false.
// Hack for old php versions to use boolval()
if (!function_exists(‘boolval’)) function boolval($val) return (bool) $val;
>
>
?>
function is_true($val, $return_null=false) <
$boolval = ( is_string($val) ? filter_var($val, FILTER_VALIDATE_BOOLEAN, FILTER_NULL_ON_FAILURE) : (bool) $val );
return ( $boolval===null && !$return_null ? false : $boolval );
>
is_true(new stdClass); // true
is_true([1,2]); // true
is_true([1]); // true
is_true([0]); // true
is_true(42); // true
is_true(-42); // true
is_true(‘true’); // true
is_true(‘on’) // true
is_true(‘off’) // false
is_true(‘yes’) // true
is_true(‘no’) // false
is_true(‘ja’) // false
is_true(‘nein’) // false
is_true(‘1’); // true
is_true(NULL); // false
is_true(0); // false
is_true(‘false’); // false
is_true(‘string’); // false
is_true(‘0.0’); // false
is_true(‘4.2’); // false
is_true(‘0’); // false
is_true(»); // false
is_true([]); // false
I believe that the double negation !! can perform the same task with the same result if your PHP is not up2date
May the life be good to you.
Php value to bool
Cast a string to binary using PHP < 5.2.1
I found it tricky to check if a posted value was an integer.
is_int ( $_POST [ ‘a’ ] ); //false
is_int ( intval ( «anything» ) ); //always true
?>
A method I use for checking if a string represents an integer value.
$foo [ ‘ten’ ] = 10 ; // $foo[‘ten’] is an array holding an integer at key «ten»
$str = » $foo [ ‘ten’]» ; // throws T_ENCAPSED_AND_WHITESPACE error
$str = » $foo [ ten ] » ; // works because constants are skipped in quotes
$fst = (string) $foo [ ‘ten’ ]; // works with clear intention
?>
It seems (unset) is pretty useless. But for people who like to make their code really compact (and probably unreadable). You can use it to use an variable and unset it on the same line:
$hello = ‘Hello world’ ;
print $hello ;
unset( $hello );
$hello = ‘Hello world’ ;
$hello = (unset) print $hello ;
?>
Hoorah, we lost another line!
It would be useful to know the precedence (for lack of a better word) for type juggling. This entry currently explains that «if either operand is a float, then both operands are evaluated as floats, and the result will be a float» but could (and I think should) provide a hierarchy that indicates, for instance, «between an int and a boolean, int wins; between a float and an int, float wins; between a string and a float, string wins» and so on (and don’t count on my example accurately capturing the true hierarchy, as I haven’t actually done the tests to figure it out). Thanks!
May be expected, but not stated ..
Casting to the existing (same) type has no effect.
$t = ‘abc’; // string ‘abc’
$u=(array) $t; // array 0 => string ‘abc’ $v=(array) $u; // array 0 => string ‘abc’
Correct me if I’m wrong, but that is not a cast, it might be useful sometimes, but the IDE will not reflect what’s really happening:
class MyObject /**
* @param MyObject $object
* @return MyObject
*/
static public function cast ( MyObject $object ) return $object ;
>
/** Does nothing */
function f () <>
>
class X extends MyObject /** Throws exception */
function f () < throw new exception (); >
>
$x = MyObject :: cast (new X );
$x -> f (); // Your IDE tells ‘f() Does nothing’
?>
However, when you run the script, you will get an exception.
In my much of my coding I have found it necessary to type-cast between objects of different class types.
More specifically, I often want to take information from a database, convert it into the class it was before it was inserted, then have the ability to call its class functions as well.
The following code is much shorter than some of the previous examples and seems to suit my purposes. It also makes use of some regular expression matching rather than string position, replacing, etc. It takes an object ($obj) of any type and casts it to an new type ($class_type). Note that the new class type must exist:
Looks like type-casting user-defined objects is a real pain, and ya gotta be nuttin’ less than a brain jus ta cypher-it. But since PHP supports OOP, you can add the capabilities right now. Start with any simple class.
class Point protected $x , $y ;
public function __construct ( $xVal = 0 , $yVal = 0 ) $this -> x = $xVal ;
$this -> y = $yVal ;
>
public function getX () < return $this ->x ; >
public function getY () < return $this ->y ; >
>
$p = new Point ( 25 , 35 );
echo $p -> getX (); // 25
echo $p -> getY (); // 35
?>
Ok, now we need extra powers. PHP gives us several options:
A. We can tag on extra properties on-the-fly using everyday PHP syntax.
$p->z = 45; // here, $p is still an object of type [Point] but gains no capability, and it’s on a per-instance basis, blah.
B. We can try type-casting it to a different type to access more functions.
$p = (SuperDuperPoint) $p; // if this is even allowed, I doubt it. But even if PHP lets this slide, the small amount of data Point holds would probably not be enough for the extra functions to work anyway. And we still need the class def + all extra data. We should have just instantiated a [SuperDuperPoint] object to begin with. and just like above, this only works on a per-instance basis.
C. Do it the right way using OOP — and just extend the Point class already.
class Point3D extends Point protected $z ; // add extra properties.
public function __construct ( $xVal = 0 , $yVal = 0 , $zVal = 0 ) parent :: __construct ( $xVal , $yVal );
$this -> z = $zVal ;
>
public function getZ () < return $this ->z ; > // add extra functions.
>
$p3d = new Point3D ( 25 , 35 , 45 ); // more data, more functions, more everything.
echo $p3d -> getX (); // 25
echo $p3d -> getY (); // 35
echo $p3d -> getZ (); // 45
?>
Once the new class definition is written, you can make as many Point3D objects as you want. Each of them will have more data and functions already built-in. This is much better than trying to beef-up any «single lesser object» on-the-fly, and it’s way easier to do.
Re: the typecasting between classes post below. fantastic, but slightly flawed. Any class name longer than 9 characters becomes a problem. SO here’s a simple fix:
function typecast($old_object, $new_classname) if(class_exists($new_classname)) // Example serialized object segment
// O:5:»field»:9: $old_serialized_prefix = «O:».strlen(get_class($old_object));
$old_serialized_prefix .= «:\»».get_class($old_object).»\»:»;
$old_serialized_object = serialize($old_object);
$new_serialized_object = ‘O:’.strlen($new_classname).’:»‘.$new_classname . ‘»:’;
$new_serialized_object .= substr($old_serialized_object,strlen($old_serialized_prefix));
return unserialize($new_serialized_object);
>
else
return false;
>
Thanks for the previous code. Set me in the right direction to solving my typecasting problem. 😉
If you have a boolean, performing increments on it won’t do anything despite it being 1. This is a case where you have to use a cast.
I have 1 bar.
I now have 1 bar.
I finally have 2 bar.
Checking for strings to be integers?
How about if a string is a float?
/* checks if a string is an integer with possible whitespace before and/or after, and also isolates the integer */
$isInt = preg_match ( ‘/^\s*(2+)\s*$/’ , $myString , $myInt );
echo ‘Is Integer? ‘ , ( $isInt ) ? ‘Yes: ‘ . $myInt [ 1 ] : ‘No’ , «\n» ;
/* checks if a string is an integer with no whitespace before or after */
$isInt = preg_match ( ‘/^4+$/’ , $myString );
echo ‘Is Integer? ‘ , ( $isInt ) ? ‘Yes’ : ‘No’ , «\n» ;
/* When checking for floats, we assume the possibility of no decimals needed. If you MUST require decimals (forcing the user to type 7.0 for example) replace the sequence:
4+(\.9+)?
with
2+\.7+
*/
/* checks if a string is a float with possible whitespace before and/or after, and also isolates the number */
$isFloat = preg_match ( ‘/^\s*(7+(\.2+)?)\s*$/’ , $myString , $myNum );
echo ‘Is Number? ‘ , ( $isFloat ) ? ‘Yes: ‘ . $myNum [ 1 ] : ‘No’ , «\n» ;
/* checks if a string is a float with no whitespace before or after */
$isInt = preg_match ( ‘/^2+(\.8+)?$/’ , $myString );
echo ‘Is Number? ‘ , ( $isFloat ) ? ‘Yes’ : ‘No’ , «\n» ;
Convert string to boolean in PHP
This article demonstrates how to convert a string to a boolean in PHP.
1. Using filter_var() function
The filter_var() function filters a variable using a specified filter and returns the filtered data. To convert a string to a boolean, you can call filter_var() with the FILTER_VALIDATE_BOOLEAN filter. It returns true for string values like 1 , true , on , and yes , and false otherwise. If FILTER_VALIDATE_BOOLEAN is used with the FILTER_NULL_ON_FAILURE flag, false is returned only for 0 , false , off , no , » , and null is returned for everything else.
This results in below output:
true => bool(true)
'1' => bool(true)
'on' => bool(true)
'On' => bool(true)
'ON' => bool(true)
'true' => bool(true)
'True' => bool(true)
'TRUE' => bool(true)
'yes' => bool(true)
'Yes' => bool(true)
'YES' => bool(true)
false => bool(false)
'false' => bool(false)
'False' => bool(false)
'FALSE' => bool(false)
'no' => bool(false)
'No' => bool(false)
'NO' => bool(false)
'off' => bool(false)
'Off' => bool(false)
'OFF' => bool(false)
'' => bool(false)
'0' => bool(false)
'foo' => NULL
'0.0' => NULL
'NAN' => NULL
Note: As of PHP 8.0.0, you can use FILTER_VALIDATE_BOOL filter, which is an alias for FILTER_VALIDATE_BOOLEAN . Note that the case is ignored when filtering strings.
2. Using === operator
In PHP, strings are always evaluated to true unless they are falsey. In other words, using the equality operator, only two strings, » and ‘0’ , return false when compared to the boolean true ( » == true, and ‘0’ == true ). However, the identity operator ( === ) can be used to obtain a boolean value based on a specific string value. For example,