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Whether php can change the constant value, many novices are not very clear about this, in order to help you solve this problem, the following editor will explain in detail for you, people with this need can come to learn, I hope you can gain something.

Php cannot change the value of a constant. Constants are immutable quantities that cannot be modified, redefined, or undefined once they are defined; they are usually used to store data that is neither changed nor desired. Data types can be integers, floats, strings, Boolean, and arrays.

Operating environment of this tutorial: windows7 system, PHP7.1 version, DELL G3 computer

The constant corresponding to a variable is a constant, which is an unchangeable quantity. Once a constant is defined in PHP, it cannot be modified or undefined.

PHP constants are usually used to store data that is neither changed nor desired, which can only be data of four scalar data types: integer, floating-point, string, and Boolean, but the constant supports array since PHP7.

Compared with variables, constants have the following characteristics:

The constant is not preceded by a dollar sign ($)

Constants can only be defined with define () and const

The scope of constants is global

Once a constant is defined, it cannot be redefined or undefined.

How do I define a constant?

Please refer to the article "how to set constants in php"

How to determine whether a constant exists?

To determine whether a constant has been defined, you can use the defined () function. The syntax format of the function is as follows:

Defined (string $name)

Where $name is the name of the constant to be judged, and the function returns a value of type bool. If the constant is defined, it returns true. If it is not defined, it returns false. The sample code is as follows:

Output result:

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