c++-重載等號，數組，指針，字符串類

重載

• 重載=操做符
  • 1先釋放舊對象資源
  • 2用一個對象=給另一個對象
  • 3函數返回值當左值 返回一個引用
  • 4 數組類 Array& operator=(Array& a1);
  • 5 字符串類：MyString& operator=(const MyString& obj);
  • char& operator const;
• 運算符重載難點
  • 重載=操做符
    • 1先釋放舊對象資源
    • 2用一個對象=給另一個對象
    • 3函數返回值當左值 返回一個引用
    • 4 數組類 Array& operator=(Array& a1);
    • 5 字符串類：MyString& operator=(const MyString& obj);
  • char& operator const;
  • 重載[]數組下標
    • 1 返回元素的引用，支持a[i]當左值 a[i]右值
    • 2 數組類 int& operator;
    • 3 字符串類 char& operator const;
  • && 和 || 不能被重載
  • ()重載
• 案例：數組類 運算符重載優化
• 案例：字符串類 運算符重載

等號運算符重載

• 重載=操做符
  • 1 先釋放舊對象資源
  • 2 用一個對象=給另一個對象
  • 3 函數返回值當左值 返回一個引用
  • 4 數組類 Array& operator=(Array& a1);
  • 5 字符串類：MyString& operator=(const MyString& obj);
  • char& operator 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;

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

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

        //2 先將自身的額外開闢的空間回收掉
        if (this->name != NULL) {
            delete[] this->name;
            this->name = NULL;
            this->id = 0;
        }

        //3 執行深拷貝
        this->id = another.id;

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


        //4 返回自己
        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 = 賦值操做符



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


    return 0;
}

自定義數組類運用重載

main.cpp

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

using namespace std;



int main(void)
{

 MyArray array1(10);//開闢10元素的數組

    //賦值操做
    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;

        //給space開闢空間
        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;

        //深拷貝
        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;

        //深拷貝
        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 << "遍歷整個數組 " << endl;
    //array.getLen(); //getLen(&array);
    for (int i = 0; i < array.getLen(); i++) {
        os << array[i] <<" ";//array.operator[]( i)
    }

    os << "調用的<<操做符重載" << endl;

    return os;
}

istream &operator>>(istream &is, MyArray &array)
{
    cout << "請輸入" << array.getLen() << "個數" << 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;
};

重載小括號

#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);
    
    //將一個對象 當成一個普通函數來調用。
                    //稱這種對象是 仿函數，僞函數, 函數對象
     

    cout << value << endl;

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


    return 0;
}

重載new和delete運算符

#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;
    }

    //重載的new操做符 依然會觸發對象的構造函數
    void * operator new(size_t size)
    {
        cout << "重載了new操做符" << endl;
        return malloc(size);
    }

    void *operator new[](size_t size)
    {
        cout << "重載了new[]操做符" << endl;
        return malloc(size);
    }
    void operator delete(void * p)
    {
        cout << "重載了delete操做符" << endl;
        if (p != NULL) {
            free(p);
            p = NULL;
        }
    }

    void operator delete[](void *p)
    {
        cout << "重載了delete[]操做符" << 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;
}

重載&&和||（不建議重載）

#define _CRT_SECURE_NO_WARNINGS
#include <iostream>


using namespace std;


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

    Test operator+(Test &another)
    {
        cout << "執行了+操做符重載" << endl;
        Test temp(this->value + another.value);
        return temp;
    }

    bool operator&&(Test &another)
    {
        cout << "執行了&&操做符重載" << endl;
        if (this->value && another.value) {
            return true;
        }
        else {
            return false;
        }

    }

    bool operator||(Test &another)
    {
        cout << "重載了||操做符" << 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);

    //重載&&操做符，並不會發生短路現象。

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

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

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


    return 0;
}

自定義智能指針

#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;
}

自定義字符串類

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);
    }
}

//初始化時候被調用的
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 << "執行了析構函數" << 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 將s以前的字符串釋放掉
    if (s.str != NULL) {
        delete[] s.str;
        s.str = NULL;
        s.len = 0;
    }

    //2 經過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); //建立一個長度是len的string對象
    MyString(const char *str);
    MyString(const MyString &another);
    ~MyString();

    //重載操做符[]
    char &operator[](int index);



    //重載操做符>>
    friend istream & operator>>(istream &is, MyString &s);

    //重載=操做符
    MyString & operator=(const MyString &another);

    //重載==操做符

    //重載!=操做符


    //重載+操做符
    MyString operator+(MyString &another);


    //重載操做符<<
    friend ostream & operator<<(ostream &os, MyString&s);

private:
    int len;
    char *str;
};