Suppose we have a variable that should not change its value in all project, we can define a variable for it, but it is not correct, because we can change it by accident in the project. For it, Php have constants.
Constants is the named of a value that does not change during the execution of the program.
In order to create a constant we use define() function, in the following format.
define (name, value, caseSensitive)
name - is a name of constant, which must comply with the same rules as the other names in PHP .
value - value of constant.
caseSensitive - Optional parameter, it specifies whether the constant name should be case-insensitive (true) or not (false).
"pi", 3.14, true); echo(pi); // output 3.14 echo (PI); // output 3.14define(
Constants are like variables except.
- Constants have not $ sign
- Constants can be defined only by using the define () function, instead of assigning values
- Constants can be defined and accessed anywhere in project, which means that they are automatically global
- Constants cannot change value, after defining
Be careful, with the name of constants, __NAME__, is valid name for constant, but php have some Magic Constants, that is like __constantName__ syntax, and if one day php provides a magical constant __NAME__ that will break your script.
About magical constants we will talk later.