The Return Value of the C ++ const function must be a const reference.

Compiled correctlyCode:

 

# Include <stdio. h> # include <string. h ># include <iostream> using namespace STD; Class t {public: T (string p) {ptext = P;} const char & operator [] (int pos) const {return ptext [POS];} string ptext ;}; int main () {string S = "ABCD"; t (s ); // T [0] = 'T'; // The value of printf ("% s \ n", S. c_str ());}

Compile the error code:

 

 

# Include <stdio. h> # include <string. h ># include <iostream> using namespace STD; Class t {public: T (string p) {ptext = P;} Char & operator [] (int pos) const // The return type is not const compilation error {return ptext [POS] ;}string ptext ;}; int main () {string S = "ABCD "; t (s); // T [0] = 'T'; // The value of printf ("% s \ n", S. c_str ());}