Question

Please help me with the following problem:

I have the following classes:

class ChemicalElement
{
private:
    std::string _name;
    void Init(const std::string& name);
public:
    ChemicalElement(const std::string& name);
    ChemicalElement(const ChemicalElement& ce);
};

class CombinationRule
{
private:
    ChemicalElement _ce1;
    ChemicalElement _ce2;
    void Init(const ChemicalElement& ce1, const ChemicalElement& ce2);
public:
    CombinationRule(const ChemicalElement& ce1, const ChemicalElement& ce2);
    CombinationRule(const CombinationRule& rule);
};

The implementation is obvious. I intended to initialize the CombinationRule using the Init method to minimize code duplication. Alas, if I do not use “member initialization list” in each constructor the compiler complains with “error C2512: ‘ChemicalElement’ : no appropriate default constructor available”. Is there an elegant way to solve this error instead of using a default constructor or member initialization list?
BTW: if there are any other problems in the classes definition please add it too. Since I’m revisiting C++ I want to be aware of them.

Answer 1

You should implement constructors of CombinationRule as follows so they will use appropriate constructors of ChemicalElement:

CombinationRule::CombinationRule(const ChemicalElement& ce1, 
  const ChemicalElement& ce2) : _ce1(ce1), _ce2(ce2) 
{ 
  ... 
}

CombinationRule::CombinationRule(const CombinationRule& rule) : 
  _ce1( rule._ce1 ), _ce2( rule._ce2 )
{
  ...
}