C++语言基础(02)

1.可变参数

void func(int i,...)
{
    //可变参数指针
    va_list args_p;
    //开始读取可变参数，i是最后一个固定参数
    va_start(args_p,i);
    int a = va_arg(args_p,int);
    char b = va_arg(args_p, char);
    int c = va_arg(args_p, int);
    cout << a << endl;
    cout << b << endl;
    cout << c << endl;
    //结束
    va_end(args_p);
}

void main(){
    func(9,20,'b',30);
    system("pause");
}

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2.构造函数、析构函数、拷贝构造函数

构造函数

class Teacher{
private:
    char *name;
    int age;
public:
    // 1  无参构造函数（写了，就会覆盖默认的无参构造函数）
    Teacher(){
        cout << "无参构造函数" << endl;
    }
   //2 无参构造函数赋默认值
    Teacher(){
        this->name = (char*)malloc(100);
        strcpy(name,"jack walson");
        age = 20;
        cout << "无参构造函数" << endl;
    }
    //有参构造函数会覆盖默认的构造函数
    Teacher(char *name, int age){
        this->name = name;
        this->age = age;
        cout << "有参构造函数" << endl;
    }

    //析构函数
    //当对象要被系统释放时，析构函数被调用
    //作用：善后处理
    ~Teacher(){
        cout << "析构" << endl;
        //释放内存
        free(this->name);
    }
        
};

void main(){
    // Teacher t1;
    Teacher t2("yuehan",20);

    //另外一种调用方式
    Teacher t3 = Teacher("jack",21);
    system("pause");
}

拷贝构造函数

class Teacher{
private:
    char *name;
    int age;
public:
    Teacher(char *name, int age){
        this->name = name;
        this->age = age;
        cout << "有参构造函数" << endl;
    }
    //拷贝构造函数（值拷贝）
    //默认拷贝构造函数，就是值拷贝
    Teacher(const Teacher &obj){
        this->name = obj.name;
        this->age = obj.age;
        cout << "拷贝构造函数" << endl;
    }
    void myprint(){
        cout << name << "," << age << endl;
    }
};

Teacher func1(Teacher t){
    t.myprint();
    return t;
}

void main(){
    Teacher t1("rose",20);

    //拷贝构造函数被调用的场景
    //1.声明时赋值
    //Teacher t2 = t1;
    //t2.myprint();
    //2.作为参数传入，实参给形参赋值
    func1(t1);
    //3.作为函数返回值返回，给变量初始化赋值
    //Teacher t3 = func1(t1);

    //这里不会被调用
    //Teacher t1 ;
    //Teacher t2;
    //t1 = t2;

    system("pause");
}

//浅拷贝（值拷贝）问题

class Teacher{
private:
    char *name;
    int age;
public:
    Teacher(char *name, int age){
        this->name = (char*)malloc(100);
        strcpy(this->name,name);
        this->age = age;
        cout << "有参构造函数" << endl;
    }   
    ~Teacher(){
        cout << "析构" << endl;
        //释放内存
        free(this->name);
    }
    void myprint(){
        cout << name << "," << age << endl;
    }
};

void func(){
    Teacher t1("rose", 20);

    Teacher t2 = t1;
    t2.myprint();
}

void main(){
    func();

    system("pause");
}

//深拷贝

class Teacher{
private:
    char *name;
    int age;
public:
    Teacher(char *name, int age){
        int len = strlen(name);
        this->name = (char*)malloc(len+1);
        strcpy(this->name, name);
        this->age = age;
        cout << "有参构造函数" << endl;
    }
    ~Teacher(){
        cout << "析构" << endl;
        //释放内存
        free(this->name);
    }
    //深拷贝
    Teacher(const Teacher &obj){
        //复制name属性
        int len = strlen(obj.name);
        this->name = (char*)malloc(len+1);
        strcpy(this->name,obj.name);
        this->age = obj.age;
    }
    void myprint(){
        cout << name << "," << age << endl;
    }
};

void func(){
    Teacher t1("rose", 20);

    Teacher t2 = t1;
    t2.myprint();
}

void main(){
    func();

    system("pause");
}