Type Juggling
PHP does not require explicit type definition in variable declaration. In this case, the type of a variable is determined by the value it stores. That is to say, if a string is assigned to variable $var, then $var is of type string. If afterwards an int value is assigned to $var, it will be of type int.
PHP may attempt to convert the type of a value to another automatically in certain contexts. The different contexts which exist are:
- Numeric
- String
- Logical
- Integral and string
- Comparative
- Function
Hinweis: When a value needs to be interpreted as a different type, the value itself does not change types.
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.
Numeric contexts
This is the context when using an arithmetical operator.
In this context if either operand is a float (or not interpretable as an int), both operands are interpreted as floats, and the result will be a float. Otherwise, the operands will be interpreted as ints, and the result will also be an int. As of PHP 8.0.0, if one of the operands cannot be interpreted a TypeError is thrown.
String contexts
This is the context when using echo, print, string interpolation, or the string concatenation operator.
In this context the value will be interpreted as string.
Logical contexts
This is the context when using conditional statements, the ternary operator, or a logical operator.
In this context the value will be interpreted as bool.
Integral and string contexts
This is the context when using a bitwise operators.
In this context if all operands are of type string the result will also be a string. Otherwise, the operands will be interpreted as ints, and the result will also be an int. As of PHP 8.0.0, if one of the operands cannot be interpreted a TypeError is thrown.
Comparative contexts
This is the context when using a comparison operator.
The type conversions which occur in this context are explained in the Comparison with Various Types table.
Function contexts
This is the context when a value is passed to a typed parameter, property, or returned from a function which declares a return type.
In this context, when coercive typing mode is active (the default), only scalar values may be converted to another scalar value. For simple types declarations the behaviour is as follows:
- bool type declaration: value is interpreted as bool. int type declaration: value is interpreted as int if conversion is well-defined. I.e. the string is numeric. float type declaration: value is interpreted as float if conversion is well-defined. I.e. the string is numeric. string type declaration: value is interpreted as string.
Internal functions
automatically coerce null to scalar types,
this behaviour is DEPRECATED as of PHP 8.1.0.
Type Casting
Type casting converts the value to a chosen type by writing the type within parentheses before the value to convert.
<?php
$foo = 10; // $foo is an integer
$bar = (bool) $foo; // $bar is a boolean
?>
The casts allowed are:
(int)- cast to int(bool)- cast to bool(float)- cast to float(string)- cast to string(array)- cast to array(object)- cast to object(unset)- cast to NULL
Hinweis:
(integer)is an alias of the(int)cast.(boolean)is an alias of the(bool)cast.(binary)is an alias of the(string)cast.(double)and(real)are aliases of the(float)cast. These casts do not use the canonical type name and are not recommended.
The (real) cast alias has been deprecated as of PHP 8.0.0.
The (unset) cast has been deprecated as of PHP 7.2.0.
Note that the (unset) cast is the same as assigning the
value NULL to the variable or call.
The (unset) cast is removed as of PHP 8.0.0.
The (binary) cast and b prefix exists
for forward support. Currently (binary) and
(string) are identical, however this may change and
should not be relied upon.
Hinweis:
Whitespaces are ignored within the parentheses of a cast. Therefore, the following are two casts are equivalent:
<?php
$foo = (int) $bar;
$foo = ( int ) $bar;
?>
Casting literal strings and variables to binary strings:
<?php
$binary = (binary) $string;
$binary = b"binary string";
?>
Hinweis: 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:
Hinweis: Because PHP supports indexing into strings via offsets using the same syntax as array indexing, the following example holds true for all PHP versions:
See the section titled String access by character for more information.<?php
$a = 'car'; // $a is a string
$a[0] = 'b'; // $a is still a string
echo $a; // bar
?>
