Memory layoutĪs you know, the derived class extends the properties of the base class. When you call it with objects of type Manager and Person, they will be automatically upcasted to Employee class:Īn example of how to use upcasting with virtual functions is described in the “ C++ Polymorphism” topic. This function will work with all the classes that are derived from the Employee class. One of the biggest advantages of upcasting is the capability of writing generic functions for all the classes that are derived from the same base class. Nevertheless, when you upcast an object, you will be able to access only member functions and data members that are defined in the base class: When you use upcasting, the object is not changing. You just need to assign derived class pointer (or reference) to base class pointer: Upcasting is a process of creating a pointer or a reference of the derived class object as a base class pointer. When you use upcasting or downcasting you just “label” an object in different ways. You have to understand it before we start learning upcasting and downcasting.īoth upcasting and downcasting do not change the object by itself. Therefore, the Manager and Clerk are Persons too. The Manager takes a commission fee for every contract, and the Clerk has information about his Manager:Įmployee(string fName, string lName, double sal) We have to specify these properties only once in the Employee class:Īt the same time, the Manager and Clerk classes are different. What does it mean? It means that Manager and Clerk classes inherit properties of Employee class, which inherits properties of Person class.įor example, we don’t need to specify that both Manager and Clerk are identified by First and Last name, have a salary you can show information about them and add a bonus to their salaries. In this topic, we will use the following hierarchy of classes:Īs you can see, Manager and Clerk are both Employee. This is upcasting.ĭowncasting is an opposite process, which consists of converting base class pointer (or reference) to derived class pointer.Ĭ++ Upcasting and Downcasting should not be understood as a simple casting of different data types. It can be achieved by using Polymorphism.Ĭ++ allows that a derived class pointer (or reference) to be treated as a base class pointer. Upcasting and downcasting give a possibility to build complicated programs with a simple syntax. Tags ACCU AI Algorithms Amos Decker Apple Apple Watch AppleWatch Arthur C.Upcasting and downcasting are an important part of C++.How to calculate Fibonacci sequence for large numbers.How to write Extension Methods in F# and Swift.Book Review: Mistress of Justice, Jeffery Deaver.How to emulate C++11's 'enum class' in C++03.Using std::tie to implement operatorHow to write a Watch Face App for Apple Watch.
Book Review: The Gods of Guilt, Michael Connelly.Book Review: Bitcoin Billionaires, Ben Mezrich.Book Review: The Abduction, Mark Gimenez.( const std::shared_ptr& b )) Īuto d = std::dynamic_pointer_cast( elements ) Std::for_each( elements.begin(), elements.end(), Call base class method on all elements This question was already asked on StackOverflow and the answers pointed me at std::dynamic_pointer_cast and std::static_pointer_cast, which are analogous to static_cast/dynamic_cast for raw pointers.Įlements.push_back( std::make_shared() ) The question is – if you have a std::shared_ptr, how to cast it to a std::shared_ptr (for suitably related T1 and T2)? I found myself in a similar situation with some more modern C++, where I had a std::vector and wanted to convert each pointer to a shared_ptr in order to call into some API method. IUnknown) and then downcast to the specific interface you want using QueryInterface.
This means that it isn’t uncommon to pass an array of objects as an of pointers to base (i.e. A lot of the codebase I work on is deployed as COM servers.
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