C++ Exceptions error

Question

I have defined my own exceptions ans I get errors at compile time:

/home/me/my_proj/CMyExceptions.hpp:38:63: error: no matching function for call to ‘MyException1::MyException1()’
   MyException2(const std::string& msg) : m_msg(msg) {}
                                                   ^
/home/me/my_proj/CMyExceptions.hpp:38:63: note: candidates are:
/home/me/my_proj/CMyExceptions.hpp:23:3: note: MyException1::MyException1(const string&)
   MyException1(const std::string& msg) : m_msg(msg) {}
   ^
/home/me/my_proj/CMyExceptions.hpp:23:3: note:   candidate expects 1 argument, 0 provided
/home/me/my_proj/CMyExceptions.hpp:17:7: note: MyException1::MyException1(const MyException1&)
 class MyException1 : public std::exception
       ^

My exceptions are:

class MyException1 : public std::exception
{
private:
  std::string m_msg;

public:
  MyException1(const std::string& msg) : m_msg(msg) {}
  virtual ~MyException1() throw() {};

  virtual const char* what() const throw()
  {
    return m_msg.c_str();
  }
};

class MyException2 : public MyException1
{
private:
  std::string m_msg;

public:
  MyException2(const std::string& msg) : m_msg(msg) {}
  virtual ~MyException2() throw() {};

  virtual const char* what() const throw()
  {
    return m_msg.c_str();
  }
};

What am I doing wrong? Shall I call the parent constructor (MyException1) before initialization?

Answer 1

You have m_msg in MyException1 and put it again in MyException2. This means MyException2 actually contains two m_msg variables. Is this what you intended?

The error message is because MyException1 does not have a default constructor, so MyException2 must call its constructor in the initialization list. I suggest

class MyException2 : public MyException1
{
public:
    MyException2(const std::string& msg) : MyException1(msg) {}
};