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[];
             *data = '\0';
         }
         else
         {
             int len = strlen(pdata);
             data = new char[len+];
             strcpy(data,pdata);
         }
     }
     Mystring(const Mystring &str)
     {
         int len = strlen(str.data);
         data = new char[len+];
         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+];//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<)
         {
             perror("index is not in the cope!");
             exit();
         }else
             return *((this->data)+index);
     }

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