Question

I would like to have a design suggestion from you.

I have a set of classes in C++, every class has a bunch of variables (double and int) which determines the behavior of the algorithms they implement.

Something like this:

class Foo
{
  private:
  double value1, value2, etc...;
  public: 
  void setOptions(double val1, double val2);
  /*
  and here other methods...
  */
};

class Bar
{
  private:
  double value1, value2, etc...;
  public: 
  void setOptions(double val1, double val2);
  /*
  and here other methods...
  */
};

I would like to group all these option variables in a single class, so that is possible to dynamically change the variables of the options in the instances of the classes, but I would also like to give the value variables a default value as initialization.

I would like that the options variables are different and set with a default value at compile time for every class.

I adopted the following approach:

// Options.h
class Options
{
    public:
    Options();

    static struct FooOptions
    {
      static double option1;
      static double option2;
    } fooOptions;

    static struct BarOptions
    {
      static double option1;
      static double option2;
        // etcetera
    } barOptions;  
};

and then in the Foo and Bar classes I use the value Options::FooOptions::option1 and so on.

The problem here is that I can’t initialize those value statically.
I’m used to initialize static member outside in the .cpp file, but in my .cpp

// Options.cpp
Options::FooOptions::option1 = 1.0;

I get the following compiler
error: error: expected constructor, destructor, or type conversion before ‘=’ token

On other hand if I initialize them inside the constructor:

// Options.cpp
Options::Options()
{
    FooOptions::option1=1.0;
}

I get undefined reference error when I try to access it from my main.

I think the problem here is that I have two nested static structures. What can be here an optimal solution for this kind of design?

How would you implement a class that acts only as container of double and int values to use inside classes as parameters of algorithms?

Answer 1

// Options.cpp
Options::FooOptions::option1 = 1.0;

Add the missing “double” 🙂

double Options::FooOptions::option1 = 1.0;

should do it.