自实现string类

#include <iostream>

#include <string.h>

using namespace std;

class Mystring{

    friend istream& operator >>(istream &in,const Mystring& another);

    friend ostream& operator <<(ostream &out,const Mystring& another);

public:

    Mystring(const char *s = nullptr);

    Mystring(const Mystring& another);

    Mystring& operator =(const Mystring& another);

    ~Mystring();

    const Mystring operator +(const Mystring& another);

private:

    char *_str;

};

istream& operator >>(istream &in,const Mystring& another)

{

    in >> another._str;

    return in;

}

ostream& operator <<(ostream &out,const Mystring& another)

{

    out << another._str << endl;

    return out;

}

Mystring::Mystring(const char *s)

{

    if(s == nullptr)

    {

        _str = new char[1];

        *_str = '\0';

    }

    else

    {

        _str = new char[strlen(s)+1];

        strcpy(_str,s);

    }

}

Mystring::Mystring(const Mystring& another)

{

    _str = new char[strlen(another._str)+1];

    strcpy(this->_str,another._str);

}

Mystring& Mystring::operator =(const Mystring& another)

{

    if(this == &another)

        return *this;

    delete [] this->_str;

    this->_str = new char[strlen(another._str)+1];

    strcpy(this->_str,another._str);

    return *this;

}

Mystring::~Mystring()

{

    delete [] _str;

}

const Mystring Mystring::operator +(const Mystring& another)

{

    int len = strlen(this->_str)+strlen(another._str);

    Mystring ms;

    delete [] ms._str;

    ms._str = new char[len+1]{0};

    strcat(strcat(ms._str,this->_str),another._str);

    return ms;

}