面试：C++String类实现

 #include <iostream>
 #include <cstring>
 using namespace std;

 class CString {
 private:
     char* m_pdata;
 public:
     CString(const char* ptr = nullptr) {
         if (ptr == nullptr)  m_pdata = nullptr;
         m_pdata = new char[strlen(ptr) + ];
         strcpy(m_pdata, ptr);
     }
     CString(const CString& a) {
         if (a.m_pdata == nullptr) this->m_pdata = nullptr;
         this->m_pdata = new char[strlen(a.m_pdata) + ];
         strcpy(this->m_pdata, a.m_pdata);
     }

     CString(CString&& a){
         this->m_pdata = a.m_pdata;
         a.m_pdata = nullptr;
     }

     ~CString() {
         if (this->m_pdata){
              delete[] this->m_pdata;
         }
     }

     CString& operator=(const CString& a) {
         if (this == &a)
             return *this;

         if (this->m_pdata)
             delete[] this->m_pdata;
         this->m_pdata = new char[strlen(a.m_pdata) + ];
         strcpy(this->m_pdata, a.m_pdata);
         return *this;
     }

     CString operator+=(const CString& a) {
         if (a.m_pdata == nullptr) {
             return *this;
         } else if (this->m_pdata == nullptr) {
             return a;
         } else {
             char* tmp = this->m_pdata;
             this->m_pdata = new char[strlen(this->m_pdata) + strlen(a.m_pdata)
                     + ];
             strcpy(this->m_pdata, tmp);
             strcat(this->m_pdata, a.m_pdata);
             delete[] tmp;
             return *this;
         }
     }

     friend CString operator+(const CString& a, const CString& b) {
         char* res = new char[strlen(a.m_pdata) + strlen(b.m_pdata) + ];
         strcpy(res, a.m_pdata);
         strcat(res, b.m_pdata);
         CString cs(res);
         delete[] res;
         return cs;
     }

     friend ostream& operator<<(ostream& os, const CString& a) {
         os << a.m_pdata;
         return os;
     }
 };

 int main() {

     CString a("abc");
     CString b(a);
     a = b;
     a += b;
     CString c = a + b;
     std::cout << c << std::endl;
     std::cout << a << std::endl;

     return ;
 }