How to use static in c language

In C language, the static keyword is used to modify a variable, function or class member to have a static scope and have the following characteristics: Internal linkage: It can only be accessed or called in the file in which it is declared. Retain values: Variables and local function variables retain their values ​​until the end of the program. Class scope: Class members belong to the entire class, and all instances share the same data. Constants: static const class members can be declared as compile-time constants.

Usage of static in C language

What is static?

static is a keyword used to modify variables, functions or class members to indicate that they have static scope.

staticScope of variables

For variables, static means:

• Internal linking: staticA variable can only be accessed within the file in which it is declared.
• Retained value: staticA variable retains its value until the end of the program, even if the function it is in has exited.
• Default initialization: Global static variables are initialized to 0, and local static variables are initialized to garbage values.

The static scope of a function

For a function, static means:

• Internal linkage: staticA function can only be called within the file in which it is declared.
• Local scope: staticLocal variables of a function have the same internal scope and value retention properties as static variables.

staticscope of class members

For class members, static means:

• Class scope: staticClass members belong to the entire class, not to any specific object.
• Shared data: All class instances share the same static class members.
• Constant: static constClass members can be declared as compile-time constants.

When to use static?

Common scenarios for using static include:

• Restrict the visibility of variables or functions
• Preserve the state of function local variables
• Using shared data in a class
• Declaring compile-time constants

Example

// 外部变量，全局可见
int external_var = 10;

// 静态变量，仅在本文件中可见且保留其值
static int static_var = 20;

// 静态函数，仅在本文件中可见且局部变量保留其值
static void static_func() {
    static int local_var = 30;
    local_var++;
}

// 静态类成员，所有对象共享
class MyClass {
public:
    static int shared_var = 40;
};

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