What is the use of static variables?

Static variable is a variable that maintains a fixed storage location during the running of the program. It has the following main purposes: 1. To achieve persistent storage and access of data; 2. Between different parts of the program 3. Used to save the status information of functions; 4. Used to control the visibility and scope of functions or class members.

# Operating system for this tutorial: Windows 10 system, Dell G3 computer.

A static variable is a variable that maintains a fixed storage location during the running of the program, and its life cycle is extended to the entire running period of the program. Static variables retain their last assigned value each time they are used until explicitly reassigned. Static variables have the following main uses:

1. Maintain data persistence: The value of a static variable remains unchanged between function calls, allowing persistent storage and access of data. . When you need to share data between multiple function calls, you can use static variables to achieve this.

2. Shared data: Static variables can share data between different parts of the program. By declaring static variables, different functions or different source files can access and modify the value of the same static variable, realizing data sharing.

3. Save status information: Static variables can be used to save status information of functions. For example, in a recursive function, use static variables to save the recursive calculation results to avoid repeated calculations and improve performance.

4. Control the visible scope of a function or class member: Static variables can also be used to control the visibility and scope of a function or class member. In C language, declaring a static variable as a static variable inside a function limits its scope to only within the function in which it is declared. In C, static member variables of a class can be shared by all object instances, rather than each object having an independent copy.

It should be noted that static variables still occupy storage space in memory, and their life cycle will be extended to the entire program running period. Therefore, static variables need to be used with caution to avoid excessive Static variables cause memory waste or program logic confusion.

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