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php 变量类型转换

PHP does not require (or support) explicit type definition in variable declaration; a variable's type is determined by the context in which the variable is used. That is to say, if a string value is assigned to variable $var$varbecomes a string. If an integer value is then assigned to $var, it becomes an integer.

An example of PHP's automatic type conversion is the multiplication operator '*'. If either operand is a float, then both operands are evaluated as floats, and the result will be a float. Otherwise, the operands will be interpreted as integers, and the result will also be an integer. Note that this does not change the types of the operands themselves; the only change is in how the operands are evaluated and what the type of the expression itself is.

<?php
$foo 
"1";  // $foo is string (ASCII 49)
$foo *= 2;   // $foo is now an integer (2)
$foo $foo 1.3;  // $foo is now a float (2.6)
$foo "10 Little Piggies"// $foo is integer (50)
$foo "10 Small Pigs";     // $foo is integer (50)
?>

If the last two examples above seem odd, see String conversion to numbers.

To force a variable to be evaluated as a certain type, see the section on Type casting. To change the type of a variable, see the settype() function.

To test any of the examples in this section, use the var_dump() function.

Note:

The behaviour of an automatic conversion to array is currently undefined.

Also, because PHP supports indexing into strings via offsets using the same syntax as array indexing, the following example holds true for all PHP versions:

<?php
$a    
'car'// $a is a string
$a[0] = 'b';   // $a is still a string
echo $a;       // bar
?>

See the section titled String access by character for more information.

Type Casting

Type casting in PHP works much as it does in C: the name of the desired type is written in parentheses before the variable which is to be cast.

<?php
$foo 
10;   // $foo is an integer
$bar = (boolean) $foo;   // $bar is a boolean
?>

The casts allowed are:

  • (int), (integer) - cast to integer
  • (bool), (boolean) - cast to boolean
  • (float), (double), (real) - cast to float
  • (string) - cast to string
  • (array) - cast to array
  • (object) - cast to object
  • (unset) - cast to NULL (PHP 5)

(binary) casting and b prefix forward support was added in PHP 5.2.1

Note that tabs and spaces are allowed inside the parentheses, so the following are functionally equivalent:

<?php
$foo 
= (int) $bar;
$foo = ( int ) $bar;
?>

Casting literal strings and variables to binary strings:

<?php
$binary 
= (binary) $string;
$binary b"binary string";
?>

Note:

Instead of casting a variable to a string, it is also possible to enclose the variable in double quotes.

<?php
$foo 
10;            // $foo is an integer
$str "$foo";        // $str is a string
$fst = (string) $foo// $fst is also a string

// This prints out that "they are the same"

if ($fst === $str) {
    echo 
"they are the same";
}

?>

It may not be obvious exactly what will happen when casting between certain types. For more information, see these sections:

add a note add a note

User Contributed Notes 33 notes

Raja ¶
11 years ago
Uneven division of an integer variable by another integer variable will result in a float by automatic conversion -- you do not have to cast the variables to floats in order to avoid integer truncation (as you would in C, for example):

$dividend = 2;
$divisor = 3;
$quotient = $dividend/$divisor;
print $quotient; // 0.66666666666667
ieee at REMOVE dot bk dot ru ¶
4 years ago
There are some shorter and faster (at least on my machine) ways to perform a type cast.
<?php
$string
='12345.678';
$float=+$string
$integer=0|$string;
$boolean=!!$string;
?>
yury at krasu dot ru ¶
13 years ago
incremental operator ("++") doesn't make type conversion from boolean to int, and if an variable is boolean and equals TRUE than after ++ operation it remains as TRUE, so:

$a = TRUE; 
echo ($a++).$a;  // prints "11"
Anonymous ¶
14 years ago
Printing or echoing a FALSE boolean value or a NULL value results in an empty string:
(string)TRUE //returns "1"
(string)FALSE //returns ""
echo TRUE; //prints "1"
echo FALSE; //prints nothing!
fardelian ¶
3 years ago
Casting objects to arrays is a pain. Example:

<?php

class MyClass {

    private 
$priv 'priv_value';
    protected 
$prot 'prot_value';
    public 
$pub 'pub_value';
    public 
$MyClasspriv 'second_pub_value';

}


$test = new MyClass();
echo 
'<pre>';
print_r((array) $test);

/*
Array
(
    [MyClasspriv] => priv_value
    [*prot] => prot_value
    [pub] => pub_value
    [MyClasspriv] => second_pub_value
)
*/


?>

Yes, that looks like an array with two keys with the same name and it looks like the protected field was prepended with an asterisk. But that's not true:

<?php

foreach ((array) $test as $key => $value) {
    
$len strlen($key);
    echo 
"{$key} ({$len}) => {$value}<br />";
    for (
$i 0$i $len; ++$i) {
        echo 
ord($key[$i]) . ' ';
    }
    echo 
'<hr />';
}


/*
MyClasspriv (13) => priv_value
0 77 121 67 108 97 115 115 0 112 114 105 118
*prot (7) => prot_value
0 42 0 112 114 111 116
pub (3) => pub_value
112 117 98
MyClasspriv (11) => second_pub_value
77 121 67 108 97 115 115 112 114 105 118
*/


?>

The char codes show that the protected keys are prepended with '\0*\0' and private keys are prepended with '\0'.__CLASS__.'\0' so be careful when playing around with this.
kuzawinski dot marcin at NOSPAM dot gmail dot com ¶
2 years ago
You REALLY must be aware what you are doing, when you cast a lot  in your code. For example, you can accidentaly change FALSE to TRUE  (probably not in one line, like here):

if(TRUE === (boolean) (array) (int) FALSE) {
    kaboom();
}
philip_snyder at hotmail dot com ¶
12 years ago
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:{s:5:...   <--- Class: Field
    $old_serialized_prefix  = "O:".strlen(get_class($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. ;)
mbrowne83 (at GM) ¶
1 year ago
The code listed in some of the comments here for supposedly "casting" from one class to another using unserialize/serialize does not actually change the class of the existing object; it creates a new object. So it's not the same as a cast.
jphansen at uga dot edu ¶
5 years ago
Type casting from string to int and vice versa is probably the most common conversation. PHP does this very simply through the +. and .= operators, removing any explicit casting:

<?php
$x 
1;
var_dump($x); // int(1)
$x .= 1;
var_dump($x); // string(2) "11"; also an empty string ("") would cast to string without changing $x

$x "1";
var_dump($x);  // string(1) "1"
$x += 1;
var_dump($x); // int(2); also a zero value (0) would cast to int without changing $x
?>
Anonymous ¶
4 years ago
namaroulis stated "I found it tricky to check if a posted value was an integer"; to test if a variable is a number or a numeric string (such as form input, which is always a string), you must use is_numeric():

<?php
$_POST
['a'] = "42";

is_numeric$_POST['a'] ); // true
?>
tom5025_ at hotmail dot com ¶
12 years ago
function strhex($string)
{
   $hex="";
   for ($i=0;$i<strlen($string);$i++)
       $hex.=dechex(ord($string[$i]));
   return $hex;
}
function hexstr($hex)
{
   $string="";
   for ($i=0;$i<strlen($hex)-1;$i+=2)
       $string.=chr(hexdec($hex[$i].$hex[$i+1]));
   return $string;
}

to convert hex to str and vice versa
martinscotta at gmail dot com ¶
5 years ago
in response to bhsmither at gmail.com

It raises a warning because of the bad enquoted variable

<?php

error_reporting
E_ALL E_STRICT );

$foo['ten'] = 10;        // $foo['ten'] is an array holding an integer at key "ten"
$str "{$foo['ten']}";  // works "10"
$str "$foo[ten]";      // DO NOT work!
Anonymous ¶
5 years ago
Checking for strings to be integers?
How about if a string is a float?

<?php

/* checks if a string is an integer with possible whitespace before and/or after, and also isolates the integer */
$isInt=preg_match('/^\s*([0-9]+)\s*$/'$myString$myInt);

echo 
'Is Integer? ',  ($isInt) ? 'Yes: '.$myInt[1] : 'No'"\n";

/* checks if a string is an integer with no whitespace before or after  */
$isInt=preg_match('/^[0-9]+$/'$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:
[0-9]+(\.[0-9]+)? 
with 
[0-9]+\.[0-9]+ 
*/

/* checks if a string is a float with possible whitespace before and/or after, and also isolates the number */

$isFloat=preg_match('/^\s*([0-9]+(\.[0-9]+)?)\s*$/'$myString$myNum);

echo 
'Is Number? ',  ($isFloat) ? 'Yes: '.$myNum[1] : 'No'"\n";

/* checks if a string is a float with no whitespace before or after */
$isInt=preg_match('/^[0-9]+(\.[0-9]+)?$/'$myString);

echo 
'Is Number? ',  ($isFloat) ? 'Yes' 'No'"\n";

?>
Eric Lavoie ¶
1 year ago
(array) null
array(null)

are not the same.

var_dump((array) null) => 
array (size=0)
  empty

var_dump(array (null)) => 
array (size=1)
  0 => null
Anonymous ¶
11 years ago
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.

<html>
<body> <!-- don't want w3.org to get mad... -->
<?php
$bar 
TRUE;
?>
I have <?=$bar?> bar.
<?php
$bar
++;
?>
I now have <?=$bar?> bar.
<?php
$bar 
= (int) $bar;
$bar++;
?>
I finally have <?=$bar?> bar.
</body>
</html>

That will print

I have 1 bar.
I now have 1 bar.
I finally have 2 bar.
wbcarts at juno dot com ¶
7 years ago
WHERE'S THE BEEF?

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.
<?php
class Point {
  protected 
$x$y;

  public function 
__construct($xVal 0$yVal 0) {
    
$this->$xVal;
    
$this->$yVal;
  }
  public function 
getX() { return $this->x; }
  public function 
getY() { return $this->y; }
}


$p = new Point(2535);
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.
<?php
class Point3D extends Point {
  protected 
$z;                                // add extra properties...

  
public function __construct($xVal 0$yVal 0$zVal 0) {
    
parent::__construct($xVal$yVal);
    
$this->$zVal;
  }
  public function 
getZ() { return $this->z; }  // add extra functions...
}

$p3d = new Point3D(253545);  // 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.
rmirabelle ¶
5 years ago
The object casting methods presented here do not take into account the class hierarchy of the class you're trying to cast your object into.

/**
     * Convert an object to a specific class.
     * @param object $object
     * @param string $class_name The class to cast the object to
     * @return object
     */
    public static function cast($object, $class_name) {
        if($object === false) return false;
        if(class_exists($class_name)) {
            $ser_object     = serialize($object);
            $obj_name_len     = strlen(get_class($object));
            $start             = $obj_name_len + strlen($obj_name_len) + 6;
            $new_object      = 'O:' . strlen($class_name) . ':"' . $class_name . '":';
            $new_object     .= substr($ser_object, $start);
            $new_object     = unserialize($new_object);
            /**
             * The new object is of the correct type but
             * is not fully initialized throughout its graph.
             * To get the full object graph (including parent
             * class data, we need to create a new instance of 
             * the specified class and then assign the new 
             * properties to it.
             */
            $graph = new $class_name;
            foreach($new_object as $prop => $val) {
                $graph->$prop = $val;
            }
            return $graph;
        } else {
            throw new CoreException(false, "could not find class $class_name for casting in DB::cast");
            return false;
        }
    }
hek at theeks dot net ¶
7 years ago
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!
namaroulis at gmail dot com ¶
5 years ago
I found it tricky to check if a posted value was an integer.

<?php

$_POST
['a'] = "42";

is_int$_POST['a'] ); //false
is_intintval"anything" ) ); //always true
?>

A method I use for checking if a string represents an integer value.

<?php
function check_int$str )
                {
                    return  
is_numeric$str ) && intval$str ) - $str == 0;
                }

?>
hemi68 at hotmail dot com ¶
4 years ago
Cast a string to binary using PHP < 5.2.1

$binary = unpack('c*', $string);
toma at smartsemantics dot com ¶
11 years ago
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:

function ClassTypeCast(&$obj,$class_type){
    if(class_exists($class_type,true)){
        $obj = unserialize(preg_replace"/^O:[0-9]+:\"[^\"]+\":/i", 
          "O:".strlen($class_type).":\"".$class_type."\":", serialize($obj)));
    }
}
alexgr at gmail dot com ¶
8 years ago
For a Cast to a User Defined Object you can define a cast method:

class MyObject {
    /**
     * @param MyObject $object
     * @return MyObject
     */
    static public function cast(MyObject $object) {
        return $object;
    }
}

In your php page code you can:
$myObject = MyObject::cast($_SESSION["myObject"]);

Then, PHP will validate the value and your IDE will help you.
dimo dot vanchev at bianor dot com ¶
12 years ago
For some reason the code-fix posted by philip_snyder at hotmail dot com [27-Feb-2004 02:08]
didn't work for me neither with long_class_names nor with short_class_names. I'm using PHP v4.3.5 for Linux.
Anyway here's what I wrote to solve the long_named_classes problem:

<?php
function typecast($old_object$new_classname) {
    if(
class_exists($new_classname)) {
        
$old_serialized_object serialize($old_object);
        
$old_object_name_length strlen(get_class($old_object));
        
$subtring_offset $old_object_name_length strlen($old_object_name_length) + 6;
        
$new_serialized_object  'O:' strlen($new_classname) . ':"' $new_classname '":';
        
$new_serialized_object .= substr($old_serialized_object$subtring_offset);
        return 
unserialize($new_serialized_object);
     } else {
         return 
false;
     }
}

?>
miracle at 1oo-percent dot de ¶
10 years ago
If you want to convert a string automatically to float or integer (e.g. "0.234" to float and "123" to int), simply add 0 to the string - PHP will do the rest.

e.g.

$val = 0 + "1.234";
(type of $val is float now)

$val = 0 + "123";
(type of $val is integer now)
edgar dot klerks at gmail dot com ¶
7 years ago
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:

Without cast: 

<?php

$hello 
'Hello world';
print 
$hello;
unset(
$hello);

?>

With the unset cast: 

<?php

$hello 
'Hello world';
$hello = (unset) print $hello;

?>

Hoorah, we lost another line!
davaakhuu at outlook dot com ¶
1 year ago
Type Juggling<br/>
   <?php $count "2 cats"?>
   Type: <?php echo gettype($count); ?><br/>
   <?php $count += 3?>
   Type: <?php echo gettype($count); ?><br/> 
   <?php $cats "I have " $count "cats."?>
   Cats: <?php echo gettype($cats); ?><br/>
   <br/>
   Type Casting<br/>
   <?php settype($count"integer"); ?>
   count: <?php echo gettype($count); ?><br/>

   <?php $count2 = (string)$count?>
   count: <?php echo gettype($count); ?><br/>
   count2: <?php echo gettype($count2); ?><br/>

   <?php $test1 3?>
   <?php $test2 3?>
   <?php settype($test1"string"); ?>
   <?php (string)$test2?>
   test1: <?php echo gettype($test1); ?><br/>
   test2: <?php echo gettype($test2); ?><br/>
post_at_henribeige_dot_de ¶
13 years ago
If you want to do not only typecasting between basic data types but between classes, try this function. It converts any class into another. All variables that equal name in both classes will be copied.

function typecast($old_object, $new_classname) {
  if(class_exists($new_classname)) {
    $old_serialized_object = serialize($old_object);
    $new_serialized_object = 'O:' . strlen($new_classname) . ':"' . $new_classname . '":' . 
                             substr($old_serialized_object, $old_serialized_object[2] + 7);
    return unserialize($new_serialized_object);
  }
  else
    return false;
}

Example:

class A {
  var $secret;
  function A($secret) {$this->secret = $secret;}
  function output() {echo("Secret class A: " . $this->secret);}
}

class B extends A {
  var $secret;
  function output() {echo("Secret class B: " . strrev($this->secret));}
}

$a = new A("Paranoia");
$b = typecast($a, "B");

$a->output();
$b->output();
echo("Classname \$a: " . get_class($a) . "Classname \$b: " . get_class($b));

Output of the example code above:

Secret class A: Paranoia
Secret class B: aionaraP
Classname $a: a
Classname $b: b
berniev ¶
11 months ago
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'  <-- now an array
$v=(array) $u;  // array 0 => string 'abc'  <-- unchanged
bhsmither at gmail.com ¶
6 years ago
<?php
$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
?>
kajsunansis at that gmail ¶
7 years ago
json_decode users consider this, when casting stdClass to array:
<?php
$obj 
= new stdClass();
$obj->{"2"} = "id";
$arr = (array) $obj;
$result = isset($arr["2"]) || array_key_exists(2$arr); // false
?>
..though casting is at least 2x faster than foreach.
lucazd at gmail dot com ¶
7 years ago
@alexgr (20-Jun-2008)

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:

<?php
class MyObject {
    
/**
     * @param MyObject $object
     * @return MyObject
     */
    
static public function cast(MyObject $object) {
        return 
$object;
    }
    
/** Does nothing */
    
function f() {}
}

class 
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.
Jeffrey ¶
7 years ago
IMAGINATION REQUIRED...

We can be a witness to PHP's 'type-jugglin' in real-time with a simple implementation of a MemoryMap. For the sake our purposes, pretend that this is an empty MemoryMap.
+-------+------+------+-------+
| index | $var | type | value |
+-------+------+------+-------+
|     1 |  --- | NULL |  null |
|     2 |  --- | NULL |  null |
|     3 |  --- | NULL |  null |
|     4 |  --- | NULL |  null |
+-------+------+------+-------+

<?php
# create some variables...
$a 10;
$b "Hello";
$c = array(55.4598.65);
# Now look at map...
?>
+-------+-------+---------+--------+
| index |  $var |    type |  value |
+-------+-------+---------+--------+
|     1 |    $a | INTEGER |     10 |
|     2 |    $b |  STRING |  Hello |
|     3 | $c[0] |   FLOAT |  55.45 |
|     4 | $c[1] |   FLOAT |  98.65 |
+-------+-------+---------+--------+
<?php
# Now, change the variable types...
$a "Bye";
$b 2;
$c[0] = "Buy";
$c[1] = "Now!";
#Look at map...
?>
+-------+-------+---------+--------+
| index |  $var |    type |  value |
+-------+-------+---------+--------+
|     1 |    $a |  STRING |    Bye | <- used to be INTEGER
|     2 |    $b | INTEGER |      2 | <- used to be STRING
|     3 | $c[0] |  STRING |    Buy | <- used to be FLOAT
|     4 | $c[1] |  STRING |  Right | <- used to be FLOAT
+-------+-------+---------+--------+
nullhilty at gmail dot com ¶
7 years ago
Just a little experiment on the (unset) type cast:

<?php
$var 
1;
$var_unset = (unset) $var;
$var_ref_unset &= (unset) $var;
var_dump($var);
var_dump($var_unset);
var_dump($var_ref_unset);
?>

output:
int(1)
NULL
int(0)


来自  http://php.net/manual/en/language.types.type-juggling.php#language.types.typecasting

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