1.思维导图：

2.myString:

#include <iostream>
#include <cstring>
#include <cstdlib>

using namespace std;


class myString
{
private:
    char *str;          //记录c风格的字符串
    int size;            //记录字符串的实际长度
public:
    //无参构造
    myString():size(10)
    {
        str = new char[size];         //构造出一个长度为10的字符串
        strcpy(str,"");         //赋值为空串
    }
    //有参构造
    myString(const char *s)          //string  s("hello world")
    {
        size = strlen(s);
        str = new char[size+1];
        strcpy(str, s);
    }

    myString(const myString &other):str(new char(*other.str)),size(other.size)//拷贝构造
    {
        cout<<"拷贝构造"<<endl;
        strcpy(str, other.str);
    }

    ~myString()                    //析构函数
    {
        delete str;
    }

    myString & operator=(const myString &other)//拷贝赋值函数
    {
        if(this!=&other)
        {
            this->size=other.size;
        }
        if(this->str!=NULL)
        {
            delete this->str;
        }
        this->str=new char(*other.str);
        cout<<"拷贝赋值"<<endl;
        strcpy(str, other.str);
        return *this;
    }

    bool empty()const//判空函数
    {
        return !strlen(this->str);
    }

    int str_size()const
    {
        return strlen(this->str);
    }

    char *c_str()           //c_str函数
    {
        return this->str;
    }

    char &at(int pos)       //at函数
    {
        return *(this->str+pos-1);
    }
    //加号运算符重载
    myString operator+(const myString &R)const
    {
        myString temp;
        strcat(temp.str,this->str);
        strcat(temp.str,R.str);
        temp.size=this->size+R.size;
        return temp;
    }
    //加等于运算符重载
    myString &operator+=(const myString &R)
    {
        strcat(this->str,R.str);
        this->size=R.size+this->size;
        return *this;
    }
    //关系运算符重载（>）
    bool operator>(const myString &R)const
    {
        if(strcmp(this->str,R.str)>0)
        {
            return true;
        }
        else
        {
            return false;
        }
    }
    //中括号运算符重载
    char &operator[](int pos)const
    {
        return *(this->str+pos-1);
    }

    void show()
    {
        cout<<"str="<<str<<"    size="<<size<<endl;
    }
};

int main()
{

    myString s("yjh");
    s.show();
    myString s1=s;
    s1.show();
    myString s2;
    s2=s;
    s2.show();
    myString s3;
    if(s1.empty())
        cout<<"s1为空"<<endl;
    else
        cout<<"s1非空"<<endl;
    if(s3.empty())
        cout<<"s3为空"<<endl;
    else
        cout<<"s3非空"<<endl;
    cout<<"s1.str_size="<<s1.str_size()<<endl;
    cout<<"s3.str_size="<<s3.str_size()<<endl;

    cout<<"s1第一位为："<<s1[1]<<"   第二位为："<<s1[2]<<"   第三位为："<<s1[3]<<endl;
    s2=s+s1;
    s2.show();
    s1+=s;
    s1.show();
    if(s1>s2)
    {
        cout<<"s1>s2"<<endl;
    }else
    {
        cout<<"s1<=s2"<<endl;
    }
    if(s1>s)
    {
        cout<<"s1>s"<<endl;
    }else
    {
        cout<<"s1<=s"<<endl;
    }
    return 0;
}