The application scene of C++ const pointer

In C++ code, there is a class named Base. The const Base *p1 pointer cannot call the set method, but can call the get method. However, the get method must be declared as const.

We can use it as a data receiver, and because of the existence of const, the receiver cannot change the data inside now.

Example:

#include <iostream>
using namespace std;

class Base {
private:
    int value;

public:
    Base(int val = 0) : value(val) {}

    void setValue(int val) {
        value = val;
    }

    int getValue() const {
        return value;
    }

    int getValueNonConst() {
        return value;
    }
};

int main() {
    Base obj(42);

    // 创建const指针
    const Base* p1 = &obj;

    // 以下操作是允许的：
    cout << "通过const指针调用const方法: " << p1->getValue() << endl;

    // 以下操作会编译错误，因为const指针不能调用非const方法：
    // p1->setValue(100);        // 错误！const指针不能调用非const方法
    // p1->getValueNonConst();   // 错误！const指针不能调用非const方法

    // 普通指针的对比
    Base* p2 = &obj;
    p2->setValue(100);          // 允许
    cout << "通过普通指针修改后: " << p2->getValue() << endl;

    return 0;
}

/*
通过const指针调用const方法: 42
通过普通指针修改后: 100
*/