Can a C++ function be declared static? What are the characteristics of static functions?

Static functions are declared static in C and have the following characteristics: they are only visible in the file in which the function is declared, do not belong to any class, memory is allocated when the program starts, and non-static members cannot be accessed. For example, a code snippet that uses a static function to calculate the area of ​​a circle can efficiently calculate the area of ​​a circle given a given radius.

Static functions in C

Static function declaration

Functions in C can be declared as static functions , just add the static keyword before the function, the syntax is as follows:

static void function_name();

Characteristics of static functions

Static functions have the following characteristics:

• Scope: Only visible within the file where the function is located.
• Bind to class: Does not belong to any class or object.
• Memory management: Saved in the static area, memory is only allocated once when the program starts, and will not be created or destroyed with function calls.
• Non-static members cannot be accessed: Since static functions do not belong to any class, non-static members (including data members and non-static methods) cannot be accessed.

Practical case

Consider the following code example that uses a static function to calculate the area of ​​a circle:

#include <iostream>
#include <cmath>

// 静态函数计算圆形的面积
static double calculate_area(double radius) {
    return M_PI * pow(radius, 2);
}

int main() {
    double radius;
    std::cout << "输入圆形半径：";
    std::cin >> radius;

    // 调用静态函数
    double area = calculate_area(radius);

    std::cout << "圆形的面积为：" << area << " 平方单位" << std::endl;

    return 0;
}

Output:

输入圆形半径：5
圆形的面积为：78.5398 平方单位

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