Question

I want to do the following:

class ErrorBase 
{
  public:
    void SetError(unsigned errorCode)
    {
      mErrorCode = errorCode;
    }

    char const* Explanation(unsigned errorCode) const
    {
      return errorExplanations[errorCode];
    }

  private:
    char const* errorExplanations[];
    unsigned mErrorCode;

};

class MyError : virtual public ErrorBase
{
  public:
    enum ErrorCodes {
      eNone,
      eGeneric,
      eMySpecificError
    };

    MyError() 
    { 

      // I want this to refer to the parent class's attribute, 
      // such that when Explanation() is executed, it uses this
      errorExplanations = {
        "no error",
        "error in MyClass",
        "specific error"
      }
    }
    ~MyError() { }
};

But I get the following error on the line declaring errorExplanations in the child class:

error: expected primary-expression before ‘{‘ token

How do I declare errorExplanations in the child class such that I can instantiate a child, and call myChild.Explanation() and get one of the error strings defined in the child’s constructor?

Any suggestions/corrections regarding my usage of const, virtual, public, etc are appreciated, Thanks!

Answer 1

Either you pass the array of error messages to the base class in its constructor (syntax may not be perfect but hopefully you get the idea):

class ErrorBase {
  public:
    ErrorBase(char const* errorExplanations[]) {
      this->errorExplanations = errorExplanations;
    }
    ...
  private:
    char const* errorExplanations[];
    ...
};

class MyError : virtual public ErrorBase {
  public:
    ...
    MyError() :
      ErrorBase( {
        "no error",
        "error in MyClass",
        "specific error"
      } )
    { }
    ...
};

Or you make Explanation virtual and provide the desired implementation in the derived class:

class ErrorBase {
  public:
    ...
    virtual char const* Explanation(unsigned errorCode) const = 0;
  protected:
    unsigned mErrorCode;
};

class MyError : virtual public ErrorBase {
  public:
    ...
    MyError() :
      errorExplanations( {
        "no error",
        "error in MyClass",
        "specific error"
      } )
    { }

    virtual char const* Explanation(unsigned errorCode) const {
      return errorExplanations[errorCode];
    }
    ...
  private:
    char const* errorExplanations[];
};