Can You Create a Vector of Abstract Classes in C ?

Vector of Abstract Classes in C : A Primer

In C , abstract classes provide a way to define interfaces without implementation, allowing derived classes to inherit and implement specific behaviors. However, unlike in C#, where interfaces can be instantiated directly, abstract classes in C cannot be.

The Problem

Consider the following C example:

class IFunnyInterface
{
public:
    virtual void IamFunny() = 0;
};

This abstract class represents an interface with a single method, IamFunny. Now, let's say we want to create a vector of objects that implement this interface, such as:

std::vector<IFunnyInterface> funnyItems;

This code will result in the following compiler error:

error C2259: 'IFunnyInterface' : cannot instantiate abstract class

This error occurs because C does not allow instantiation of abstract classes.

A Workaround

One workaround is to replace the abstract class with a concrete class that throws an exception when attempting to call an unimplemented method:

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

While this workaround allows the vector instantiation, it introduces a potential pitfall: code that attempts to access the methods of an IFunnyInterface object will need to handle the exception.

An Alternative Solution

A more elegant solution is to use a vector of pointers to abstract classes:

std::vector<IFunnyInterface*> ifVec;

This approach allows for polymorphic behavior and avoids the object slicing problem that can occur with direct value storage.

By understanding the limitations of abstract class instantiation in C , you can employ appropriate workarounds or use alternatives to achieve the desired functionality in your code.

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