PHP does not require (or it 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 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.
$data = “0”; // $data is string (ASCII 48)
$data += 2; // $data is now an integer (2)
$data = $data + 1.3; // $data is now a float (3.3)
$data = 5 + “10 Little Piggies”; // $data is integer (15)
$data = 5 + “10 Small Pigs”; // $data 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, use 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:
$a = ‘car’; // $a is a string
$a[0] = ‘b’; // $a is still a string
echo $a; // bar
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.
$data = 10; // $data is an integer
$data2 = (boolean) $data ; // $data2 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)
