How Can I Use a Vector of Abstract Classes in C ?

Abstract Classes and Vectors

In object-oriented programming, an abstract class serves as a blueprint for defining common behavior among various classes. However, one may encounter an issue when attempting to instantiate a vector of abstract classes.

The error "cannot instantiate abstract class" arises because a vector requires its elements to be concrete objects that can be allocated memory. Abstract classes, on the other hand, are not intended to be instantiated directly since they contain pure virtual functions that must be overridden.

To overcome this, a workaround involves replacing the abstract class with a concrete class that implements the necessary virtual functions, as suggested:

class IFunnyInterface
{
public:
    virtual void IamFunny() { throw new std::exception("not implemented"); }
};

However, this approach may not be desirable as it introduces unnecessary implementation details that could be avoided in an abstract base class.

A more C -idiomatic solution is to use a vector of pointers to abstract classes:

std::vector<ifunnyinterface> ifVec;</ifunnyinterface>

This allows for polymorphic behavior and prevents object slicing. Pointers to abstract classes are able to store objects of derived classes, enabling you to retain access to the specific functionality of each type.

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