The relationship and difference between PHP constants and variables

Through the previous series of studies, you have learned about PHP constants and variables, so do you know the relationship and difference between PHP constants and variables? Don’t worry, let’s take a look at the relationship and difference between PHP constants and variables

Let’s learn more aboutWhat are variables and constants

During the execution of the program, the value stored in a variable can be changed at any time, but the value stored in a constant cannot be changed.

Variables are used to store temporary data information. When a variable is defined, the system will automatically allocate a storage space for the variable to store the variable's value. We can assign a value to a variable when we define it. If we need to change the value of the variable, we only need to assign it

again. Temporary data information or processing procedures can be stored in variables.

Constants are used to store data information that does not change frequently. You can assign a value to a constant when you define it. During the entire execution period of the program, this assignment is valid and the constant cannot be assigned again.

Let’s firstLook at the difference between the two from the definition of PHP constants and variables:

Constant: In PHP we use the define() function to define constants​​​​​​​​ ：Detailed explanation of the definition and usage examples of PHP constants

Variables: All variables in PHP start with $, followed by the name of the variable, and assign a value to the variable. For details, see:Detailed explanation of the definition and usage examples of PHP variables

From the definition of PHP constants and variables, we can get:

1. There is nothing in front of the constant Dollar sign ($);
   

2. Constants can only be defined with the define() function, not through assignment statements;

Then Take a look at the difference between php constants and variables after they are defined:

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

Variable: Variable refers to the amount that the value can change during the execution of the program. It is opposite to the constant we are talking about.

In this way we can get the following result:

Constants cannot be changed as long as they are defined, but variables can be changed.

Look againThe values ​​of constants and variables:

Constant: The value of a constant can only be a scalar, that is, it can be an integer floating point type Boolean null string etc., it cannot be an array object resource, and the variable can be all data types of PHP (PHP’s eight data types).

Let’s take a look at the scope of PHP constants and variables:

Scope of constants: No matter where they are defined, constants can be called directly without scope.

Scope of variables: The variable is valid in that scope in which it is defined. For example, a variable defined in a function is only valid in the function.

Summary:

Through the above content, we can summarize a few points on the difference between php constants and variables:

1. There is no dollar sign ($) in front of the constant
2. Constants can only be defined using the define() function, not through assignment statements
3. Constants can be defined anywhere regardless of the rules of variable scope. Visit
4. Once a constant is defined, it cannot be redefined or undefined
5. The value of a constant can only be a scalar

Related recommendations: Related video tutorial recommendations: "php.cn Dugu Jiujian (4)-php video tutorial": Variables and constants

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