In PHP, a constant is a read-only variable whose value cannot be changed during the script execution. Once a constant is defined, it cannot be redefined or undefined.
To create a constant in PHP, we use the define() function. The syntax of the define() function is as follows:
define(name, value, case-insensitive)
Where:
- name: Represents the name of the constant.
- value: Represents the value of the constant.
- case-insensitive: Optional parameter that specifies whether the constant name should be case-insensitive. By default, it is set to false.
Here's an example of how to define and use a constant in PHP:
define("PI", 3.141592653589793); // defines a constant named PI with value 3.141592653589793
//Using the constant
echo "The value of PI is: " . PI;
Output:
The value of PI is 3.141592653589793
In the code above, we defined a constant named PI with the value of 3.1415926535889793. We then used the constant in the echo statement.
Note that constant names in PHP are case-sensitive by default. If you want to make them case-insensitive, pass true as the third argument to the define() function:
define("EXAMPLE", "This is an example"); // defines a constant named EXAMPLE with value "This is an example"
define("example", "This is another example", true); // defines a constant named example with value "This is another example" (case-insensitive)
//Using the constant
echo EXAMPLE . "
";
echo example;
Output:
This is an example
This is another example
In the code above, we defined two constants - EXAMPLE and example. The first one is case-sensitive and the second one is case-insensitive. We then used both of the constants in the echo statements.