笔记

深浅模式

总结 ​

  • =，[]，() 和 -> 操作符只能通过成员函数进行重载

  • << 和 >>只能通过全局函数配合友元函数进行重载

  • 不要重载 && 和 || 操作符，因为无法实现短路规则

常规建议

运算符和结合性

强化训练 ​

字符串类封装

cpp
#define _CRT_SECURE_NO_WARNINGS
#pragma once

#include <iostream>
using namespace std;

class MyString {
    friend ostream& operator<<(ostream& out, MyString& str);
    friend istream& operator>>(istream& in, MyString& str);

public:
    MyString(const char*);
    MyString(const MyString&);
    ~MyString();

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

    //=号重载
    MyString& operator=(const char* str);
    MyString& operator=(const MyString& str);

    //字符串拼接 重载+号
    MyString operator+(const char* str);
    MyString operator+(const MyString& str);

    //字符串比较
    bool operator==(const char* str);
    bool operator==(const MyString& str);

private:
    char* pString;//指向堆区空间
    int m_Size;   //字符串长度 不算'\0'
};
cpp
#include "MyString.h"

//左移运算符
ostream& operator<<(ostream& out, MyString& str) {
    out << str.pString;
    return out;
}
//右移运算符
istream& operator>>(istream& in, MyString& str) {
    //先将原有的数据释放
    if (str.pString != NULL) {
        delete[] str.pString;
        str.pString = NULL;
    }
    char buf[1024];//开辟临时的字符数组，保存用户输入内容
    in >> buf;

    str.pString = new char[strlen(buf) + 1];
    strcpy(str.pString, buf);
    str.m_Size = strlen(buf);

    return in;
}

//构造函数
MyString::MyString(const char* str) {
    this->pString = new char[strlen(str) + 1];
    strcpy(this->pString, str);
    this->m_Size = strlen(str);
}

//拷贝构造
MyString::MyString(const MyString& str) {
    this->pString = new char[strlen(str.pString) + 1];
    strcpy(this->pString, str.pString);
    this->m_Size = str.m_Size;
}

//析构函数
MyString::~MyString() {
    if (this->pString != NULL) {
        delete[] this->pString;
        this->pString = NULL;
    }
}

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

MyString& MyString::operator=(const char* str) {
    if (this->pString != NULL) {
        delete[] this->pString;
        this->pString = NULL;
    }
    this->pString = new char[strlen(str) + 1];
    strcpy(this->pString, str);
    this->m_Size = strlen(str);
    return *this;
}

MyString& MyString::operator=(const MyString& str) {
    if (this->pString != NULL) {
        delete[] this->pString;
        this->pString = NULL;
    }
    this->pString = new char[strlen(str.pString) + 1];
    strcpy(this->pString, str.pString);
    this->m_Size = str.m_Size;
    return *this;
}

MyString MyString::operator+(const char* str) {
    int newsize = this->m_Size + strlen(str) + 1;
    char* temp = new char[newsize];
    memset(temp, 0, newsize);
    strcat(temp, this->pString);
    strcat(temp, str);

    MyString newstring(temp);
    delete[] temp;

    return newstring;
}

MyString MyString::operator+(const MyString& str) {
    int newsize = this->m_Size + str.m_Size + 1;
    char* temp = new char[newsize];
    memset(temp, 0, newsize);
    strcat(temp, this->pString);
    strcat(temp, str.pString);

    MyString newstring(temp);
    delete[] temp;
    return newstring;
}

bool MyString::operator==(const char* str) {
    if (strcmp(this->pString, str) == 0 && strlen(str) == this->m_Size) {
        return true;
    }

    return false;
}

bool MyString::operator==(const MyString& str) {
    if (strcmp(this->pString, str.pString) == 0 && str.m_Size == this->m_Size) {
        return true;
    }

    return false;
}
cpp
#include "MyString.h"

void test() {
    MyString str("hello World");

    cout << str << endl;

    //cout << "请输入MyString类型字符串：" << endl;
    //cin >> str;

    //cout << "字符串为： " << str << endl;

    //测试[]
    cout << "MyString的第一个字符为：" << str[0] << endl;

    //测试 =
    MyString str2 = "^_^";
    MyString str3 = "";
    str3 = "aaaa";
    str3 = str2;
    cout << "str2 = " << str2 << endl;
    cout << "str3 = " << str3 << endl;

    //测试 +
    MyString str4 = "我爱";
    MyString str5 = "北京";
    MyString str6 = str4 + str5;
    MyString str7 = str6 + "天安门";

    cout << str7 << endl;

    //测试 ==
    if (str6 == str7) {
        cout << "s6 与 s7相等" << endl;
    }
    else {
        cout << "s6 与 s7不相等" << endl;
    }
}

int main(int argc, char *argv[]) {
    test();

    system("pause");
    return 0;
}

运行结果：