Question

This is probably a basic question for a regular C++ user. Functionally, I have an ECG monitor, and want to choose which output format to use at runtime. I have set up two classes that expose the same methods and members (ECGRecordingDefaultFormat and ECGRecordingEDFFormat) eg. ->InsertMeasure, ->setFrequency, ->setPatientName etc.

I know I could define one instance of each format class type, then put in:

if (ECGFormatToUse == ECGFormat.EDF) {
    ecgDefaultFormat.InsertMeasure(x);
}
if (ECGFormatToUse == ECGFormat.Default) {
    ecgEDFFormat.InsertMeasure(x);
}

all throughout the code, but I think I might not be using C++’s dynamic typing to its full extent.

The question is: can I define just one variable in main(), and after choosing the format I want at runtime, have the code use the right class with its exposed ‘InsertMeasure’ method, avoiding a whole lot of if/else’s throughout the code?

I’d be happy with just a reference to which aspect of inheritance/polymorphism (?) I should be using, and can google away the rest.

Thanks guys.

Pete

Answer 1

You can combine the factory pattern with C++’s polymorphism.

class Base
{
   virtual void InsertMeasure() = 0; //virtual pure, make the base class abstract
};

class ECGRecordingDefaultFormat : public Base
{
   virtual void InsertMeasure();
};

class ECGRecordingEDFFormat : public Base
{
   virtual void InsertMeasure();
};

class Factory
{
   static Base* create(ECGFormat format)
   {
      if ( format == ECGFormat.EDF )
         return new ECGRecordingEDFFormat;
      if ( format == ECGFormat.Default )
         return new ECGRecordingDefaultFormat;
      return NULL;
   }
};

int main()
{
   ECGFormat format;
   //set the format
   Base* ECGRecordingInstance = Factory::create(format);
   ECGRecordingInstance->InsertMeasure();
   return 0;
}