Study notes C ++ - based and object - operator overloading

The concept of operator overloading: redefine existing operators, to impart additional features to accommodate different types of data, such as self-defined data types.

This blog is mainly recorded the learning process plus operator overloading, assignment operators, relational operators overloading, the function call operator overloading.

1. plus operator overloading

Action: two realized adding custom data type operation.

There are two implementations, member functions and achieve global functions are realized.

class Person{
public:
    Person(){};
    Person(int a,int b){
        this->m_a=a;
        this->m_b=b;
    }
//    成员函数实现+号运算符重载
    Person operator+(const Person& p){
        Person tmp;
        tmp.m_a=this->m_a+p.m_a;
        tmp.m_b=this->m_b+p.m_b;
        return tmp;
    }

public:
    int m_a;
    int m_b;
};

//全局函数实现+号运算符重载
Person operator+(const Person& p1,const Person& p2){
    Person tmp;
    tmp.m_a=p1.m_a+p2.m_a;
    tmp.m_b=p1.m_b+p2.m_b;
    return tmp;
}

void test01(){
    Person p1(2,5);
    Person p2(6,4);
//    成员函数方式，相当于p1.operator+(p2)
//    全局函数方式，相当于operator+(p1,p2)
    Person p3=p1+p2;
    cout<<p3.m_a<<"---"<<p3.m_b<<endl;
}

2. assignment operator overloading

If the class has attributes open area in the heap, and the compiler is provided a shallow copy, the copy will have problems doing depth assignment, this time need to reload the assignment operator.

class Student{
public:
    Student(int age){
        m_age=new int(age);
    }
//    重载赋值运算符
    Student& operator=(Student &student){
        if(m_age!=NULL){
            delete m_age;
            m_age=NULL;
        }
//        提供深拷贝，解决浅拷贝的问题
        m_age=new int(*student.m_age);
//        返回自身
        return *this;
    }
    ~Student(){
        if(m_age!=NULL){
            delete m_age;
            m_age=NULL;
        }
    }
public:
    int *m_age;
};

void test01(){
    Student student1(24);
    Student student2(15);
    student2=student1;
    cout<<"student1的年龄："<<*student1.m_age<<endl;
    cout<<"student2的年龄："<<*student2.m_age<<endl;
}

3. Relationship operator overloading

Action: two let-defined data type comparison operation.

class Student{
public:
    Student(string name,int age){
        this->m_name=name;
        this->m_age=age;
    }
//    重载==运算符
    bool operator==(Student &student){
        if(this->m_name==student.m_name&&this->m_age==student.m_age){
            return true;
        }else{
            return false;
        }
    }
//    重载!=运算符
    bool operator!=(Student &student){
        if(this->m_name==student.m_name&&this->m_age==student.m_age){
            return false;
        }else{
            return true;
        }
    }
public:
    string m_name;
    int m_age;
};

void test01(){
    Student student1("li",20);
    Student student2("wang",20);

    if(student1==student2){
        cout<<"student1和student2相等"<<endl;
    }else{
        cout<<"student1和student2不相等"<<endl;
    }

    if(student1!=student2){
        cout<<"student1和student2不相等"<<endl;
    }else{
        cout<<"student1和student2相等"<<endl;
    }
}

4. The function call operator overloading

Function call operator () overload may occur, because of the similarity use after use and function of the overload, so called functor.

class Myadd{
public:
    int operator()(int a,int b){
        return a+b;
    }
};

void test01(){
    Myadd myadd;
    int result=myadd(5,6);
    cout<<"result="<<result<<endl;
//    匿名对象调用，匿名对象当前行代码执行完后立即执行销毁操作
    int res=Myadd()(20,30);
    cout<<"res="<<res<<endl;
}