Thread: Question about unions

This one has stumped me a bit....

I have the following bit of code :

Code:

typedef struct sField
{
    short x, y, length;
    short type;
    union data
    {
        short selection;
        std::string line;
    }
};

that produces this error message :

Code:

member 'sField::data::line' of union 'sField::data' has copy constructor

Am I correct in assuming that a union member cannot contain a class object that has a defined copy constructor?

If so, is there any way around this without using C-style strings? I would really like to use a std::string here as it would make the implementation a lot easier.

What are you actually trying to do?

It's going to eventually be part of a console based menu system. I am creating a templete class that will, among other things, allow the user to input selections for menu options. It will also allow the user to enter data into various forms and data structures. I figure that by using a union like this I can use a templete function to get user input and store it in the appropriate data type based on how the data is going to be used.

It is still very much in the begining stages and the bit of code that I posted above will get expanded with more functionallity, but I need it to be very generic so that it can be used with different data types. The short and std::string that I have listed there is just the begining.

This is also a bit of a learning exercise for me as well, so if you have and better or more efficient ideas they are most definitly welcome...

You can't put non-POD types into a union.

I am creating a templete class that will, among other things, allow the user to input selections for menu options.

OK.

It will also allow the user to enter data into various forms and data structures.

Isn't the class going to a little do much? What does various forms and data structures have to do with a console menu?

Seems like a task much better suited for a set of classes that inherit from a(n abstract) base class, e.g. :

Code:

class BaseField
{ 
protected:
    short x, y, length;
public:
    virtual ~BaseField(); 
};

class ShortField: public BaseField
{
private:
    short d;
public:
    short GetData() { return d; }
};


class StringField: public BaseField
{
private:
    std::string d;
public:
    std::string GetData() { return d; }
};

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Mats