25.防止空指针调用成员函数

程序1：

#pragma warning(disable:4996)
#include <iostream>
using namespace std;

class Maker
{
public:
    Maker()
    {
        a = 20;
    }
    
    void printMaker()//this指针
    {
        if (this == NULL)
        {
            cout << "this==NULL" << endl;
            return;
        }
        //cout << this->a << endl;
    }

private:
    int a;
};

void test()
{
    Maker *m = NULL;
    m->printMaker();
}

int main()
{
    test();
    system("pause");
    return EXIT_SUCCESS;
}

输出结果：

this==NULL
请按任意键继续. . .