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This article introduces the relevant knowledge of "how to understand the definition of PHP constant and how to obtain its value". In the operation of actual cases, many people will encounter such a dilemma, so let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!

What is the PHP constant?

Constants correspond to variables. Constants are simply immutable quantities and can be regarded as identifiers of simple values. It is important to note that, unlike variables, constants can be used throughout the script and are automatically global, that is, they can be used throughout the script.

A constant usually consists of numbers, letters, and an underscore (_), but to be exact, the constant name of a legal constant must start with an underscore, and the constant name does not need to be modified with the $modifier. its name is expressed in the regular expression we knew before:

[a-zA-Z0-9 _\ x7f -\ xff] *

When a data is not changed or we don't want it to change again, we can use the PHP constant to store it. The data types of such data may be integer, floating-point, string, Boolean, and array types.

Definition of PHP constant and acquisition of its value

There are two ways to set definition constants in PHP, which are the const definition and the define () function definition, and the constant () function to set the defined constants, which we will introduce respectively.

Definition of PHP constant

1) const keyword

Using the const keyword to define a constant is the easiest step, similar to assignment. Let's take a look at the basic syntax format of the const keyword as follows:

Const constant name = constant value

Next, let's take a look at defining constants through the const keyword through an example, as follows:

Output result:

2) define () function

The basic syntax format of the define () function is as follows:

Define (string $name, mixed $value [, bool $case_insensitive = false])

It is important to note that the parameter $name is a required parameter to represent the constant name, that is, the marker. The parameter $value is also required to represent the value of the constant. The parameter $case_insensitive is optional, and when set to TRUE, the constant is case-insensitive. By default, it is case sensitive.

Next, let's take a look at the application of the define () function through an example, as follows:

Output result:

From the above example, you can see that constants can be defined in PHP through the define () function and const. Next, let's take a look at how to get the value of a constant after a constant is defined in PHP.

The acquisition of PHP constant value

Constant () function

After we have defined a constant in PHP, we can use this constant through the constant () function, which has the following basic syntax format:

Constant (string $name)

It should be noted that the parameter $name represents the name of the variable you want to operate on, or it can be a variable that stores the name of the constant, but if the constant is not defined, the result returned will be an error.

Next, let's take a look at the use of the constant () function through an example, as follows

Output result:

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