Can We Extend the C Standard Library Through Inheritance?

Extending the C Standard Library through Inheritance

The common perception is that the C standard library is not meant to be extended via inheritance. However, the existence of std::exception challenges this notion. Hence, the following questions arise:

Can Standard Library Classes Be Extended by Inheritance?

Apart from std::exception, it is not clear which other standard library classes are intended for inheritance. A practical approach to determine suitable candidates is as follows:

• Check for Virtual Methods: Classes with virtual methods are potential candidates for base classes.
• Avoid Classes with Friend Declarations: Encapsulation issues may make inheritance problematic.
• Consider Templates: Customization through specializations may be preferable to inheritance for templates.
• Be Wary of Policy-Based Mechanisms: These mechanisms suggest that inheritance is not advisable.

Implications of Inheriting from Standard Library Classes

When inheriting from a standard library class like std::exception, it is debatable whether the subclass must adhere to the original interface. However, the "Liskov Substitution Principle" (LSP) suggests that the behavior of the subclass should be consistent with that of the base class as far as the client is concerned.

Therefore, it is considered a best practice to ensure that the subclass's what() member function returns a non-null pointer, even though the Standard does not explicitly require this for subclasses of std::exception.

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