What is the function and usage of static in C language

The role and usage of static in c language: 1. Variable scope; 2. Life cycle; 3. Internal functions; 4. Modify global variables; 5. Modify functions; 6. Other uses; detailed introduction: 1 . Variable scope. When a variable is preceded by the static keyword, the scope of the variable is limited to the file in which it is declared. In other words, the variable is a "file-level scope", which is useful for preventing "duplication of variables". "Definition" problem is very useful; 2. Life cycle, static variables are initialized once when the program starts executing, and destroyed when the program ends, etc.

The operating system for this tutorial: Windows 10 system, DELL G3 computer.

In C language, the static keyword has many uses, mainly used to control the life cycle and visibility of variables, and to control the storage of variables in functions. The following are the functions and usage of static:

1. Variable scope: When there is the static keyword before a variable, the scope of the variable is limited to the file in which it is declared. In other words, this variable is "file-level scope". This is useful for preventing "double definition" problems of variables.

#include <stdio.h>  
  
void func() {  
    static int x = 0; // 文件级作用域  
    x++;  
    printf("%d\n", x);  
}  
  
int main() {  
    func(); // 输出: 1  
    func(); // 输出: 2  
    return 0;  
}

2. Life cycle: Static variables are initialized once when the program starts executing, and destroyed when the program ends. In other words, the life cycle of static variables is the execution time of the entire program. This makes static variables particularly suitable for saving the global state of a program while it is running.

3. Inside the function: Inside the function, the static keyword is used to declare a local variable, which means that this variable is only visible inside the function where it is declared, and its life cycle is the entire program execution time. Such local variables are often called "static local variables".

#include <stdio.h>  
  
void func() {  
    static int x = 0; // 静态局部变量  
    x++;  
    printf("%d\n", x);  
}  
  
int main() {  
    func(); // 输出: 1  
    func(); // 输出: 2  
    return 0;  
}

4. Modify global variables: In the global scope, static can be used to modify variables so that the scope of this variable is limited to the file in which it is declared. This is similar to the role of local variables and can avoid incorrect references to this variable in other files.

5. Modified function: static can also modify a function so that this function can only be called internally in the file in which it is declared. This is often used to implement modular programming, limiting the role of a function to a certain scope.

6. Other uses: static can also be used to modify other data types such as arrays and pointers, but these uses are relatively rare. In some special cases, such as to implement advanced features such as singleton mode or thread-local storage, the static keyword may also be used.

In general, the static keyword is a very useful tool in the C language. It can provide better encapsulation and data hiding, making the program structure clearer and easier to maintain. However, if used improperly, it may also lead to reduced readability and maintainability of the code, so it needs to be used with caution.

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