一、仿照string类，完成myString 类

mystring.h

#ifndef MYSTRING_H
#define MYSTRING_H

#include <iostream>
#include <cstring>

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
        cout<<"无参构造"<<endl;
    }
    //有参构造
    myString(const char *s)          //string  s("hello world")
    {
        size = strlen(s);
        str = new char[size+1];
        strcpy(str, s);
        cout<<"有参构造"<<endl;
    }

    //拷贝构造
    myString(const myString &other)
    {
        str=new char[other.size];
        strcpy(str,other.str);
        this->size=other.size;
        cout<<"拷贝构造"<<endl;
    }

    //析构函数
    ~myString()
    {
        delete str;
        cout<<"析构函数"<<endl;
    }
    //拷贝赋值函数
    myString operator=(const myString &other);
    //判空函数
    bool string_empty()const;
    //size函数
    int string_size()const;
    //c_str函数
    const char* c_str()const;
    //at函数
    char &at(int pos);
    //加号运算符重载
    myString operator+(const myString &other)const;
    //加等于运算符重载
    myString operator+=(const myString &other);
    //关系运算符重载（>）
    bool operator>(const myString &other)const;
    //中括号运算符重载
    char operator[](int index)const;
};

#endif // MYSTRING_H

mystring.cpp:

#include "mystring.h"

//拷贝赋值函数
myString myString::operator=(const myString &other)
{
    if(this!=&other)
    {
        if(str!=NULL)
        {
            delete str;
        }
        str=new char[other.size];
        strcpy(str,other.str);
        this->size=other.size;
    }
    return *this;
}
//判空函数
bool myString::string_empty()const
{
    return strcmp(str,"")==0;
}
//size函数
int myString::string_size()const
{
    return size;
}
//c_str函数
const char* myString::c_str()const
{
    return str;
}
//at函数
char &myString::at(int pos)
{
    while(1)
    {
        if(pos<0||pos>=size)
        {
            cout<<"输入格式不对,范围为0~"<<size<<endl;
        }else{
            break;
        }
    }
    return *(str+pos);
}
//加号运算符重载
myString myString::operator+(const myString &other)const
{
    myString a=*this;
    char buf[a.size];
    strcpy(buf,a.str);
    if(a.str!=NULL)
    {
        delete a.str;
    }
    a.size=a.size+other.size;
    a.str=new char[a.size];
    strcpy(a.str,buf);
    strcat(a.str,other.str);

    return a;
}
//加等于运算符重载
myString myString::operator+=(const myString &other)
{
    char buf[size];
    strcpy(buf,str);
    if(str!=NULL)
    {
        delete str;
    }
    size=size+other.size;
    str=new char[size];
    strcpy(str,buf);
    strcat(str,other.str);

    return *this;
}
//关系运算符重载（>）
bool myString::operator>(const myString &other)const
{
    return strcmp(str,other.str)>0;
}
//中括号运算符重载
char myString::operator[](int index)const
{
    while(1)
    {
        if(index<0||index>=size)
        {
            cout<<"输入格式不对,范围为0~"<<size<<endl;
        }else{
            break;
        }
    }
    return *(str+index);
}

main.cpp:

#include "mystring.h"

int main()
{
    myString a("hello world");
    cout<<"字符串a为 "<<a.c_str()<<endl;
    cout<<"字符串大小为"<<a.string_size()<<endl;
    a.at(0)='H';
    cout<<"字符串a为 "<<a.c_str()<<endl;
    myString b;
    cout<<"字符串b为空？"<<b.string_empty()<<endl;
    b=a;
    cout<<"字符串b为 "<<b.c_str()<<endl;
    myString c=a+b;
    cout<<"字符串c为 "<<c.c_str()<<endl;
    myString d("hahaha");
    d+=a;
    cout<<"字符串d为 "<<d.c_str()<<endl;
    cout<<"字符串d比a大？ "<<d.operator>(a)<<endl;
    return 0;
}

运行结果：

二、思维导图：day3补充： 有道云笔记 day4：有道云笔记