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, $var becomes 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 addition operator '+'. If either operand is a float , then both operands are evaluated as float s, and the result will be a float . Otherwise, the operands will be interpreted as integer s, 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 = "0"; // $foo is string (ASCII 48)
$foo += 2; // $foo is now an integer (2)
$foo = $foo + 1.3; // $foo is now a float (3.3)
$foo = 5 + "10 Little Piggies"; // $foo is integer (15)
$foo = 5 + "10 Small Pigs"; // $foo is integer (15)
?>
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 string s 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
?>
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:
(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 string s and variables to binary string s:
<?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: