string容器的简单实现

1.业务使用main.cpp

#include "pch.h"
#include <iostream>

int main()
{
    mystring s1;//无参构造函数
    mystring s2("s2");//有参构造函数
    mystring s3 = s2;//拷贝构造函数
    mystring s4 = "s444444444";//有参构造函数

    s4 = s2;//mysring& operator=(mysring &s)
    s4 = "s2222";//mystring& operator=(const char *p)

    cout << s4[0] << endl;//char& operator[](int index)

    cout << s4 << endl;//ostream& operator<<(ostream &out, mystring &s)

    if (s4 == "s2222")//bool operator==(const char *p)
    {
        cout << "相等" << endl;
    }

    if (s4 != s3)//bool operator==(mystring s)
    {
        cout << "不相等" << endl;
    }
    //cout << s4.m << endl;
    std::cout << "Hello World!
"; 
}

2.string.h

#ifndef PCH_H
#define PCH_H

// TODO: 添加要在此处预编译的标头
#include<iostream>
using namespace std;

class mystring
{
    friend ostream& operator<<(ostream &out, mystring &s);
public:
    mystring();
    mystring(const char *p);
    mystring(mystring &s);
    ~mystring();

    mystring& operator=(mystring &s);
    mystring& operator=(const char *p);
    char& operator[](int index);
    bool operator==(const char *p) const;//const修饰this的内容不能改变，编译器中默认const mystring *this修饰了this不能指向其他地方
    bool operator!=(const char *p) const;
    bool operator==(mystring s) const;
    bool operator!=(mystring s) const;


protected:
    int m_len;
    char *m_p;

};
#endif //PCH_H

3.string.cpp

#define _CRT_SECURE_NO_WARNINGS
#include "pch.h"

// 一般情况下，忽略此文件，但如果你使用的是预编译标头，请保留它。
mystring::mystring() 
{
    m_len = 0;
    m_p = new char[m_len + 1];
    strcpy(m_p, "");
}
mystring::mystring(const char *p)
{
    if (p == NULL) {
        m_len = 0;
        m_p = new char[m_len + 1];
        strcpy(m_p, "");
    }
    else
    {
        m_len = strlen(p);
        m_p = new char[m_len + 1];
        strcpy(m_p, p);
    }
}

//    mystring s3 = s2;
mystring::mystring(mystring &s)
{
    m_len = s.m_len;
    m_p = new char[m_len + 1];
    strcpy(m_p, s.m_p);
}

mystring::~mystring()
{
    if (m_p != NULL) {
        delete m_p;
        m_p = NULL;
        m_len = -1;
    }
}
//s4 = s2;
mystring& mystring::operator=(mystring &s)
{
    //把旧的内存先释放
    if (m_p != NULL) 
    {
        delete[]m_p;
        m_len = 0;
    }
    //根据传进来的参数分配内存
    m_len = s.m_len;
    m_p = new char[m_len + 1];
    strcpy(m_p, s.m_p);

    return *this;
}
mystring& mystring::operator=(const char *p)
{
    if (m_p != NULL)
    {
        delete[]m_p;
        m_len = 0;
    }

    if (p == NULL) {
        m_len = 0;
        m_p = new char[m_len + 1];
        strcpy(m_p, "");
    }
    else
    {
        m_len = strlen(p);
        m_p = new char[m_len + 1];
        strcpy(m_p, p);
    }

    return *this;
}

char& mystring::operator[](int index)
{
    return m_p[index];
}

ostream& operator<<(ostream &out, mystring &s)
{
    out << s.m_p;
    return out;
}

bool mystring::operator==(const char *p) const
{
    if (p == NULL)
    {
        if (m_len == 0)
        {
            return true;
        }
    }
    else
    {
        if (m_len == strlen(p))
        {
            return !strcmp(m_p, p);
        }
    }

    return false;
}
bool mystring::operator!=(const char *p) const
{
    return !(*this == p);
}
bool mystring::operator==(mystring s) const
{
    return !strcmp(m_p, s.m_p);
}
bool mystring::operator!=(mystring s) const
{
    return !(*this == s);
}