PHP Section 2 Data Type Conversion_PHP Tutorial

A variable is considered NULL when:

• is assigned the value NULL.

• has not been assigned a value yet.

• is unset().

NULL type has only one value, which is the case-insensitive keyword NULL (you can write it as NULL or null).

Converting a variable to the null type will delete the variable and unset its value.

Type conversion

PHP does not require (or support) explicit type definitions in variable definitions; the variable type is determined based on the context in which the variable is used. In other words, if a string value is assigned to the variable var, var becomes a string. If you assign an integer value to var, it becomes an integer.

An example of PHP's automatic type conversion is the plus sign "+". If any operand is a floating point number, all operands are treated as floating point numbers, and the result is also a floating point number. Otherwise the operands are interpreted as integers and the result is also an integer. Note that this does not change the types of the operands themselves; only how the operands are evaluated and the type of the expression itself is changed.

Type casting in PHP is very much like in C: the variable to be converted is preceded by the target type enclosed in parentheses.

• (int), (integer) - converted to integer
• (bool), (boolean) - Convert to boolean
• (float), (double), (real) - Convert to Float (float)
• (string) - Convert to string (string)
• (binary) - convert to binary string (string) (PHP 6)
• (array) - Convert to array(array)
• (object) - Convert to object (object)
• (unset) - Convert to NULL (PHP 5)

(binary) conversion will prefix the result with 'b', new in PHP 5.2.1.