What is the difference between C++ static functions and global functions?

Static functions are only visible within the class, without a class instance, and are used for tool class methods; while global functions are visible within the entire program, without a class or instance, and are used for independent functions.

The difference between C static functions and global functions

Introduction
In C, static Functions and global functions are two types of functions with different functions and scopes. Understanding the differences between them is crucial to writing clear and maintainable code.

Static functions
Static functions are similar to ordinary member functions, but they cannot access non-static member data of the class. They are typically used to implement utility class methods that do not require access to the class's state.

Declaration and Definition

class MyClass {
public:
    static int add(int a, int b) { return a + b; }
};

Scope and Callability
Static functions are only visible within the scope of the class. This means that they can be called directly by the class name without creating an instance of the class.

int result = MyClass::add(10, 20); // 输出 30

Global function
Global function does not belong to any class. They are visible throughout the scope of the program. They are used to define class-independent functionality, such as I/O operations or mathematical operations.

Declaration and Definition

int add(int a, int b) { return a + b; }

Scope and Callability
Global functions can be accessed and called from anywhere in the program.

int result = add(10, 20); // 输出 30

Difference table

Feature	Static function	Global function
Visibility	Limited to class	Program scope
Accessibility	No need for class instance	No need for class or instance
Scope	Within class	Entire program
Purpose	Tool class method	Independent function

Actual case

Example 1: Static function
Create a Math class that contains a static calculateArea function that calculates The area of ​​a circle.

class Math {
public:
    static double calculateArea(double radius) { return (3.14 * radius * radius); }
};

Call:

double area = Math::calculateArea(5); // 输出 78.5

Example 2: Global function
Define a displayMessage global function, this function Print the message passed to it.

void displayMessage(const string& message) {
  cout << message << endl;
}

Call:

displayMessage("Hello world!"); // 输出 "Hello world!"

Conclusion
Understanding the difference between static functions and global functions is essential for writing clear and maintainable C Code is crucial. Static functions are used for utility class methods within a class, while global functions are used for independent functionality available within the program scope.

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