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c++-重载等号，数组，指针，字符串类

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  • 重载=操作符
    • 1先释放旧对象资源
    • 2用一个对象=给另外一个对象
    • 3函数返回值当左值 返回一个引用
    • 4 数组类 Array& operator=(Array& a1);
    • 5 字符串类：MyString& operator=(const MyString& obj);
    • char& operator[](int index) const;
  • 运算符重载难点
    • 重载=操作符
      • 1先释放旧对象资源
      • 2用一个对象=给另外一个对象
      • 3函数返回值当左值 返回一个引用
      • 4 数组类 Array& operator=(Array& a1);
      • 5 字符串类：MyString& operator=(const MyString& obj);
    • char& operator[](int index) const;
    • 重载[]数组下标
      • 1 返回元素的引用，支持a[i]当左值 a[i]右值
      • 2 数组类 int& operator[](int i);
      • 3 字符串类 char& operator[](int index) const;
    • && 和 || 不能被重载
    • ()重载
  • 案例：数组类 运算符重载优化
  • 案例：字符串类 运算符重载

等号运算符重载

  • 重载=操作符
    • 1 先释放旧对象资源
    • 2 用一个对象=给另外一个对象
    • 3 函数返回值当左值 返回一个引用
    • 4 数组类 Array& operator=(Array& a1);
    • 5 字符串类：MyString& operator=(const MyString& obj);
    • char& operator[](int index) const;
#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <string.h>


using namespace std;

class Student
{
public:
        Student()
        {
                this->id = 0;
                this->name = NULL;
        }

        Student(int id, char *name)
        {
                this->id = id;

                //this->name = name;
                int len = strlen(name);
                this->name = new char[len + 1];
                strcpy(this->name, name);
        }

        Student(const Student &another)
        {
                this->id = another.id;

                //深拷贝
                int len = strlen(another.name);
                this->name = new char[len + 1];
                strcpy(this->name, another.name);
        }

        Student & operator=(const Student &another)
        {
                //1 防止自身赋值
                if (this == &another) {
                        return *this;
                }

                //2 先将自身的额外开辟的空间回收掉
                if (this->name != NULL) {
                        delete[] this->name;
                        this->name = NULL;
                        this->id = 0;
                }

                //3 执行深拷贝
                this->id = another.id;

                int len = strlen(another.name);
                this->name = new char[len + 1];
                strcpy(this->name, another.name);


                //4 返回本身
                return *this;
        }

        void printS()
        {
                cout << name << endl;
        }

        ~Student() {
                if (this->name != NULL) {
                        delete[] this->name;
                        this->name = NULL;
                        this->id = 0;
                }
        }
private:
        int id;
        char *name;
};

int main(void)
{

        Student s1(1, "zhang3");
        Student s2(s1);

        s2 = s1;

        Student s3(2, "li4");


        //s2 = s3 = s1;//s2 = 赋值操作符



        s1.printS();
        s2.printS();
        s3.printS();


        return 0;
}

自定义数组类运用重载

main.cpp

#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include "MyArray.h"

using namespace std;



int main(void)
{

 MyArray array1(10);//开辟10元素的数组

        //赋值操作
        for (int i = 0; i < 10; i++) {
                //array1.setData(i, i + 10);
                array1[i] = i + 10;//space[1] = 1+10
        }

        cout << "--------" << endl;

        cout << "array1:" << endl;
        for (int i = 0; i < 10; i++) {
                cout << array1[i] << " ";
        }
        cout << endl;

        MyArray array2 = array1;
        cout << "array2:" << endl;
        for (int i = 0; i < array2.getLen(); i++) {
                cout << array2[i] << " ";
        }
        cout << endl;
        

        cout << " ------------" << endl;
        MyArray array3(5);

        cin >> array3;


        cout << "array3:" << endl;
        cout << array3 << endl;
        cout << endl;

        
        if (array3 != array1)  {
                cout << "不相等" << endl;
        }
        else {
                cout << "相等 " << endl;
        }

        return 0;
}

Array.cpp

#include "MyArray.h"


MyArray::MyArray()
{
        cout << "MyArray()..." << endl;
        this->len = 0;
        this->space = NULL;
}

MyArray::MyArray(int len)
{
        if (len <= 0) {
                this->len = 0;
                return;
        }
        else {
                this->len = len;

                //给space开辟空间
                this->space = new int[this->len];
                cout << "MyArray::MyArray(int len) ..." << endl;
        }
}
MyArray::MyArray(const MyArray &another)
{
        if (another.len >= 0) {
                this->len = another.len;

                //深拷贝
                this->space = new int[this->len];
                for (int i = 0; i < this->len; i++) {
                        this->space[i] = another.space[i];
                }
                cout << "MyArray::MyArray(const MyArray &another) ..." << endl;

        }
}
MyArray::~MyArray()
{
        if (this->space != NULL) {
                delete[]this->space;
                this->space = NULL;
                len = 0;
                cout << "MyArray::~MyArray() ..." << endl;
        }
}

void MyArray::setData(int index, int data)
{
        if (this->space != NULL) {
                this->space[index] = data;
        }
}
int MyArray::getData(int index)
{
        return this->space[index];
}
int MyArray::getLen() const
{
        return this->len;
}

MyArray&  MyArray::operator=(const MyArray& another)
{
        if (this == &another) {
                return *this;
        }

        if (this->space != NULL) {
                delete[]this->space;
                this->space = NULL; 
                this->len = 0;
        }

        if (another.len >= 0) {
                this->len = another.len;

                //深拷贝
                this->space = new int[this->len];
                for (int i = 0; i < this->len; i++) {
                        this->space[i] = another.space[i];
                }
                cout << "MyArray::operator=(const MyArray& another) ..." << endl;

        }

        return *this;
}

int & MyArray::operator[](int index) const
{
        return this->space[index];
}


ostream &operator<<(ostream &os,const MyArray &array)
{
        os << "遍历整个数组 " << endl;
        //array.getLen(); //getLen(&array);
        for (int i = 0; i < array.getLen(); i++) {
                os << array[i] <<" ";//array.operator[]( i)
        }

        os << "调用的<<操作符重载" << endl;

        return os;
}

istream &operator>>(istream &is, MyArray &array)
{
        cout << "请输入" << array.getLen() << "个数" << endl;
        for (int i = 0; i < array.getLen(); i++) {
                cin >> array[i];
        }
        return is;
}


bool operator==(MyArray &array1, MyArray &array2)
{
        if (array1.len != array2.len) {
                return false;
        }

        for (int i = 0; i < array1.len; i++) {
                if (array1.space[i] != array2.space[i]) {
                        return false;
                }
        }

        return true;
}
bool MyArray::operator!=(MyArray &another)
{
        return !(*this == another);
}

Array.h

#pragma once
#include <iostream>

using namespace std;

class MyArray
{
public:
        MyArray();
        MyArray(int len);
        MyArray(const MyArray &another);
        ~MyArray();

        void setData(int index, int data);
        int getData(int index);
        int getLen() const ;

        MyArray& operator=(const MyArray& another);

        int & operator[](int index) const;

        friend ostream &operator<<(ostream &os,const MyArray &array);
        friend istream &operator>>(istream &is, MyArray &array);

        friend bool operator==(MyArray &array1, MyArray &array2);
        bool operator!=(MyArray &another);
private:
        int len;
        int *space;
};

重载小括号

#define _CRT_SECURE_NO_WARNINGS
#include <iostream>


using namespace std;

class Sqr
{
public:
        Sqr(int a) {
                this->a = a;
        }

        int operator()(int value)
        {
                return value * value;
        }

        int operator()(int value1, int value2)
        {
                return value1 * value2;
        }


private:
        int a;
};

void func(int a)
{

}

int main(void)
{
        Sqr s(10);

        int value = s(2);
        //s.operator()(2);
        
        //将一个对象 当成一个普通函数来调用。
                                        //称这种对象是 仿函数，伪函数, 函数对象
         

        cout << value << endl;

        value = s(10, 20);
        
        cout << value << endl;


        return 0;
}

重载new和delete运算符

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <iostream>
#include <fstream>


using namespace std;

class A
{
public:
        A()
        {
                cout << "A()..." << endl;
        }
        A(int a) {
                cout << "A(int)..." << endl;
                this->a = a;
        }

        //重载的new操作符 依然会触发对象的构造函数
        void * operator new(size_t size)
        {
                cout << "重载了new操作符" << endl;
                return malloc(size);
        }

        void *operator new[](size_t size)
        {
                cout << "重载了new[]操作符" << endl;
                return malloc(size);
        }
        void operator delete(void * p)
        {
                cout << "重载了delete操作符" << endl;
                if (p != NULL) {
                        free(p);
                        p = NULL;
                }
        }

        void operator delete[](void *p)
        {
                cout << "重载了delete[]操作符" << endl;
                if (p != NULL) {
                        free(p);
                        p = NULL;
                }
        }

        ~A() {
                cout << "~A().... " << endl;
        }

private:
        int a;
};

int main(void)
{
        //char *array = malloc(sizeof(char)* 80);

        //int *value_p = new int;

        A *array_p = new A[10];


        //array_p->operator new[](sizeof(A[10]));
        delete[] array_p;

        A *ap = new A(10);

        //ap->operator new(sizeof(A));

        delete ap;
        
        return 0;
}

重载&&和||（不建议重载）

#define _CRT_SECURE_NO_WARNINGS
#include <iostream>


using namespace std;


class Test
{
public:
        Test(int value) {
                this->value = value;
        }

        Test operator+(Test &another)
        {
                cout << "执行了+操作符重载" << endl;
                Test temp(this->value + another.value);
                return temp;
        }

        bool operator&&(Test &another)
        {
                cout << "执行了&&操作符重载" << endl;
                if (this->value && another.value) {
                        return true;
                }
                else {
                        return false;
                }

        }

        bool operator||(Test &another)
        {
                cout << "重载了||操作符" << endl;
                if (this->value || another.value) {
                        return true;
                }
                else {
                        return false;
                }
        }

        ~Test(){
                cout << "~Test()..." << endl;
        }
private:
        int value;
};

int main(void)
{
        int a = 1;
        int b = 20;


        Test t1(0);
        Test t2(20);

        //重载&&操作符，并不会发生短路现象。

        if (t1 && (t1+t2) ) {   //t1.operator&&(  t1.operator+(t2)  )
                cout << "为真" << endl;
        }
        else {
                cout << "为假" << endl;
        }

        cout << "------" << endl;

        if (t1 || (t1 + t2)) {//t1.operator||(  t1.operator+(t2) )
                cout << "为真" << endl;
        }
        else {
                cout << "为假" << endl;
        }


        return 0;
}

自定义智能指针

#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <memory>


using namespace std;

class A
{
public:
        A(int a)
        {
                cout << "A()..." << endl;
                this->a = a;
        }

        void func() {
                cout << "a = " << this->a << endl;
        }

        ~A() {
                cout << "~A()..." << endl;
        }
private:
        int a;
};


class MyAutoPtr
{
public:
        MyAutoPtr(A * ptr)
        {
                this->ptr = ptr;//ptr = new A(10)
        }

        ~MyAutoPtr() {
                if (this->ptr != NULL) {
                        cout << "delte ptr" << endl;
                        delete ptr;
                        this->ptr = NULL;
                }
        }

        A* operator->()
        {
                return this->ptr;
        }


        A& operator*()
        {
                return *ptr;
        }

private:
        A *ptr;
};

void test1()
{
#if 0
        A* ap = new A(10);

        ap->func();
        (*ap).func();

        delete ap;
        auto_ptr<int> ptr(new int);
#endif
        auto_ptr<A> ptr(new A(10));

        ptr->func();
        (*ptr).func();
}


void test2()
{
        MyAutoPtr my_p(new A(10));

        my_p->func(); //my_p.ptr -> func()
        (*my_p).func(); //  *ptr.func()
}
int main(void)
{
        
        //test1();
        test2();

        return 0;
}

自定义字符串类

main.cpp

#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <string>
#include "MyString.h"

using namespace std;

int main(void)
{
        string s1;
        MyString s1("abc");
        MyString s2("123");

        //cout << s1 + s2 << endl;

        cout << s1 << endl;
        cout << s2 << endl;


#if 0
        MyString s1("abc");
        MyString s2(s1);
        MyString s3 = "123";


        cout << s1 << endl;
        cout << s2 << endl;

        s1[1] = 'x';

        cout << s1 << endl;

        s1 = s3;

        cout << s1 << endl;

#endif
        return 0;
}

String.cpp

#include "MyString.h"


MyString::MyString()
{
        this->len = 0;
        this->str =NULL;
}

MyString::MyString(const char *str)
{
        if (str == NULL) {
                this->len = 0;
                this->str = new char[0 + 1];
                strcpy(this->str, "");
        }
        else {
                int len = strlen(str);
                this->len = len;

                this->str = new char[len + 1];
                strcpy(this->str, str);
        }
}

//初始化时候被调用的
MyString::MyString(const MyString &another)
{
        this->len = another.len;
        this->str = new char[this->len + 1];
        strcpy(this->str, another.str);
}



MyString::~MyString()
{
        if (this->str != NULL) {
                cout << this->str << "执行了析构函数" << endl;
                delete this->str;
                this->str = NULL; 
                this->len = 0;
        }
}

char & MyString::operator[](int index)
{
        return this->str[index];
}

MyString &  MyString::operator=(const MyString &another)
{
        if (this == &another) {
                return *this;
        }

        if (this->str != NULL) {
                delete[] this->str;
                this->str = NULL;
                this->len = 0;
        }

        this->len = another.len;
        this->str = new char[this->len + 1];
        strcpy(this->str, another.str);

        return *this;
}

ostream & operator<<(ostream &os, MyString&s)
{
        os << s.str;
        return os;
}

istream & operator>>(istream &is, MyString &s)
{
        //1 将s之前的字符串释放掉
        if (s.str != NULL) {
                delete[] s.str;
                s.str = NULL;
                s.len = 0;
        }

        //2 通过cin添加新的字符串
        char temp_str[4096] = { 0 };
        cin >> temp_str;

        int len = strlen(temp_str);
        s.str = new char[len + 1];
        strcpy(s.str, temp_str);
        s.len = len;

        return is;
}

MyString MyString::operator+(MyString &another)
{
        MyString temp;

        int len = this->len + another.len;

        temp.len = len;

        temp.str = new char[len + 1];
        memset(temp.str, 0, len + 1);
        strcat(temp.str, this->str);
        strcat(temp.str, another.str);

        return temp;
}

String.h

#pragma once
#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
using namespace std;

class MyString
{
public:
        MyString();
        //MyString(int len); //创建一个长度是len的string对象
        MyString(const char *str);
        MyString(const MyString &another);
        ~MyString();

        //重载操作符[]
        char &operator[](int index);



        //重载操作符>>
        friend istream & operator>>(istream &is, MyString &s);

        //重载=操作符
        MyString & operator=(const MyString &another);

        //重载==操作符

        //重载!=操作符


        //重载+操作符
        MyString operator+(MyString &another);


        //重载操作符<<
        friend ostream & operator<<(ostream &os, MyString&s);

private:
        int len;
        char *str;
};

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