C++ string数据类型的实现

#include <cstdlib>
#include <cstring>

class Mystring
{
public:
    Mystring(const char * pdata)
    {
        if(pdata==NULL)
        {
            data = new char[1];
            *data = '';
        }
        else
        {
            int len = strlen(pdata);
            data = new char[len+1];
            strcpy(data,pdata);
        }
    }
    Mystring(const Mystring &str)
    {
        int len = strlen(str.data);
        data = new char[len+1];
        strcpy(data,str.data);
    }

    Mystring &operator=(const Mystring &str)
    {
        if(this!=&str)
        {
            Mystring strTemp(str);
            char *pTemp = strTemp.data;
            strTemp.data = this->data;
            this->data = pTemp;
        }
        return this;
    }
    ostream & operator<<(ostream &os,const Mystring &str)
    {
        os<<str.data;
        return os;
    }
    Mystring & operator+(const Mystring & str)const
    {
        if(str.data!=NULL)
        {
            int len1 = strlen(str.data);
            int len2 = strlen(this->data);
            Mystring strTemp(*(this->data));//创建一个临时对象保存原来对象的数据
            delete []data;//删除原来的数据
            data=NULL;
            data = new char[len1+len2+2];//开闭新的空间
            strcpy(data,strTemp.data);//复制
            strcat(data,str.data);//拼接
        }
        return this;
    }

    char & operator[](int index)//char返回引用，是为了我们之后可以修改字符串
    {
        int len = strlen(data);
        if(index>len||index<0)
        {
            perror("index is not in the cope!");
            exit(0);
        }else
            return *((this->data)+index);
    }

    ~Mystring()
    {
        delete []data;
    }
private:
    char * data;
};