Default Constructors and Destructors in C : When Should I Use '=default' vs '{}'?

Differences between "=default" and "{}" for Default Constructors and Destructors

In C , the default constructor and destructor are special member functions that are automatically generated by the compiler if not explicitly defined by the user. However, for certain scenarios, it becomes necessary to override these default behaviors, raising the question of whether "=default" and "{}" offer the same functionality.

Default Destructors

If a class requires a virtual destructor but the implementation is identical to the compiler-generated version, the "=default" syntax can be used. It ensures that the compiler generates the virtual destructor without the need for an explicit definition. On the other hand, using an empty definition "virtual ~Widget() {}" achieves the same effect, with minimal typing.

Default Constructors

Unlike destructors, the impact of "=default" for default constructors is significantly different from "{}." When using "Widget() = default," the compiler automatically generates a default constructor for the class "Widget." This generated constructor behaves as if no constructor was defined by the user. Consequently, it contributes towards making the class a "trivial type" in C 11 terminology.

Conversely, "Widget() {}" creates a user-provided default constructor, which prevents the class from being considered trivial. C 11 places restrictions on trivial types, allowing operations such as memcpy for efficient initialization.

Conclusion

For virtual destructors, "=default" and "{}" behave similarly. However, for default constructors, "=default" generates a compiler-provided default constructor, while "{}" creates a user-provided one, potentially affecting the triviality of the class. The choice between "=default" and "{}" for default constructors should be based on the desired behavior and the implications for the triviality of the class.

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