c++-重载等号，数组，指针，字符串类

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 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 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;
    • 3 字符串类 char& operator 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 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;
};