What is Constant in PHP?

What is Constant in PHP?

A constant is an identifier for a data value. Once defined, the data value identified by a constant can’t be changed.

PHP supports constants with following basic rules:

A constant must be defined with the define(name, value).

For example, define(“PI”, 3.14); defines a constant named as PI to a value of 3.14.

To retrieve the value defined in a constant, you can use the constant name directly in any expression.

For example, define(“PI”, 3.14); $area = PI * $radius * $ radius; uses the value define in PI to calculate the area.

You are allowed to use any string for the constant name.

For example, define(“LONG PI”, 3.1415); defines a constant named as “LONG PI” to a value of 3.1415. But using special characters in constant names are not recommended.

If a constant name contains a special characters, you need to use the constant(name) function to retrieve the value defined in the constant.

For example, define(“LONG PI”, 3.1415); $area = constant(LONG PI) * $radius * $radius; uses the value defined in “LONG PI” to calculate the area.

If you want to know if there is constant for a given constant name, you can use the define(name) function.

For example, define(“LONG PI”, 3.1415); defined(“LONG PI”); returns TRUE. And defined(“LONG MI”); returns FALSE.

Now let’s take an example to confirm some rules mentioned above.

Click here to download example file.