PHP Data Types

Most PHP scripts deal with data in one form or another, usually stored in variables. PHP can work with different types of data. For example, a whole number is said to have an integer data type, while a string of text has a string data type.

In this article you explore PHP’s data types; look at loose typing; learn how to discover the type of a given value; and see how to change data types.

PHP’s scalar data types

Scalar data is data that only contains a single value. As of version 6, PHP features 6 scalar data types:

Type	Description	Example values
integer	A whole number	7, -23
float	A floating point number	7.68, -23.45
string	A sequence of characters	"Hello", "abc123@#$"
unicode	A sequence of Unicode characters	"Hello", "abc123@#$"
binary	A sequence of binary (non-Unicode) characters	"Hello", "abc123@#$"
boolean	Either true or false	true, false

PHP’s compound data types

Compound data can contain multiple values. PHP has 2 compound data types:

array

Can hold multiple values indexed by numbers or strings

object

Can hold multiple values (properties), and can also contain methods (functions) for working on properties

An array or object can contain multiple values, all accessed via one variable name. What’s more, those values can themselves be other arrays or objects. This allows you to create quite complex collections of data.

PHP’s special data types

As well as scalar and compound types, PHP has 2 special data types that don’t fall into the other categories:

resource

Used to access an external resource (for example, a file handle or database connection)

null

Can only contain the value null, which means “no value”

Loose typing in PHP

Some languages, such as Java, are strongly typed: once you’ve created a variable, you can’t change the type of data stored in it. PHP, in contrast, is loosely typed: you can change a variable’s data type at any time.

In the following PHP example, $x starts off by holding integer data (3). The next line appends the string “hello” to the data using the concatenation operator, which changes $x‘s value to “3hello” (a string data type). Finally, 5.67 is assigned to $x, changing its data type to a float:

$x = 3;
$x .= "hello";
$x = 5.67;

Finding out the data type of a value

You can check a value’s data type using one of the following PHP functions:

is_int( value )

Returns true if value is an integer, false otherwise

is_float( value )

Returns true if value is a float, false otherwise

is_string( value )

Returns true if value is a string, false otherwise

is_unicode( value )

Returns true if value is a Unicode string, false otherwise

is_binary( value )

Returns true if value is a binary string, false otherwise

is_bool( value )

Returns true if value is a Boolean, false otherwise

is_array( value )

Returns true if value is an array, false otherwise

is_object( value )

Returns true if value is an object, false otherwise

is_resource( value )

Returns true if value is a resource, false otherwise

is_null( value )

Returns true if value is null, false otherwise

For example, the following code displays 1 (true):

$x = 3.14;
echo is_float( $x );

Changing data types with settype()

As you’ve already seen, you can change a variable’s data type simply by assigning a new value of a different type to the variable. However, sometimes it’s a good idea to explicitly set the type of the data held by a variable. For example, if you’re handing data entered by a visitor, or passing data to another program, then it’s good to ensure that the data is of the correct type.

PHP has a function called settype() that converts a variable’s value from one data type to another:

$x = 3.14;
settype( $x, "integer" );

In the above example, $x‘s data type is changed from float to integer (with the result that $x ends up containing the value 3).

Changing data types with casting

If you just want to change a value’s type at the time you use the value, then you can use casting. This merely changes the type of the value that is to be used; the original variable remains untouched.

To cast a value, place the data type in parentheses before the value at the time you use it:

$x = 3.14;
echo (integer) $x;

The above code displays 3 (3.14 cast to an integer). However, note that $x still contains the value 3.14 after the cast operation.

You now know all about PHP data types. You’ve looked at PHP’s various scalar, compound and special data types, learned about PHP’s loose typing, and discovered how to read and change data types in your PHP scripts. Happy coding!