Question

I have two files: error.h and error.cpp. Compiling with

g++ -std=c++0x

gives me an error:

error.cpp:9:33:**call of overloaded "to_string(char*&)" is ambiguous**

How can i fix this problem?

error.h:

  1 #ifndef ERROR_H_GUARD
  2 #define ERROR_H_GUARD
  4 #include <string>
  6 class Error {
  7   public:
  8     Error(int pos, std::string& msg); 
 10     Error(int pos, char* msg); 
 12     const char* what() throw();
 14   private:
 15     std::string msg;
 17     void setMsg(int pos, std::string& msg);
 18 };
 19 
 20 #endif

error.cpp:

  2 #include "error.h"
  4 Error::Error(int pos, std::string& msg){
  5   setMsg(pos, msg);
  6 }
  8 Error::Error(int pos, char* msg) {
  9   setMsg(pos, std::to_string(msg));
 10 }   
 12 const char* Error::what() throw() {
 13   return msg.c_str();
 14 } 
 16 void Error::setMsg(int pos, std::string& msg){
 17   this->msg = std::to_string(pos) + msg + std::string("\n") + std::string(pos - 1, ' ') + std::string("^");
 18 }

Answer 1

to_string() is used to convert something which is not a string (e.g. a long, an int, etc.) into a string. You have a char*, which is a C string, and what you want to do is to create a string object out of it, not convert it.

Your compiler complains about ambiguity because it cannot find a version of to_string() for the type you are passing to it (char*), which makes sense, considering the purpose of that function.

If you declared your parameter string const& rather than string& in the corresponding overload of setMsg() (and in the constructor of Error as well), you could directly invoke it by passing C strings: a temporary of type string would be created automatically and bound to the argument of setMsg().

This way you would even get rid of the specific overload of setMsg() for C strings, which in fact does nothing but forwarding.