How to Use CRuntimeClass in Visual C++

In MFC programs, objects are created and destroyed based on the user's actions. This unpredictability makes it necessary to have a mechanism that provides dynamic runtime information about objects. This information includes the class name, extra type checking, inheritance from other classes and object creation based on a familiar name. The CRuntimeClass, which is analogous but more sophisticated than the typeid keyword of C++, does all this.

Instructions

Difficulty: Moderately Easy

Things You’ll Need:

• Microsoft Visual Studio or .NET Studio IDE
• MFC programming basics
• MFC book, such as "Visual C++ Programmer's Guide" by Beck Zaratian

1. Prepare a simple MFC program (single document, multiple document or dialog based) involving several controls.
2. Associate a class with the CRuntimeClass class. Insert the DECLARE_DYNAMIC macro inside the class definition in the class header file. Add the IMPLEMENT_DYNAMIC macro at the top of the source file of the class. The macro takes two parameters: the class in question and CObject. Now that these formalities are finished, you can provide runtime information.
3. Get the name of the MFC class by using the m_lpszClassName member. It returns an LPCSTR, which is an ASCII null-terminated string containing the class name.
4. Find the size of the class using the m_nObjectSize member. It returns an int that is the size of the object in bytes. If members of the object point to allocated memory, that memory isn't included.
5. Create a specified class dynamically at runtime. You can do this by using the CreateObject() member, which returns a pointer to a CObject.
6. Determine whether a given class is derived from a certain base class. To do this, use the IsDerivedFrom() member, which takes as parameter the CRuntimeClass* structure of the base class. It ascends the inheritance chain and returns "true" if it finds a match.
7. Use the IsKindOf() member to do type checking. It accepts as parameter a pointer to the CRuntimeClass of the associated class. "True" is returned if the types match.

Tips & Warnings

• The CRuntimeClass class contains more features than the ones mentioned in this article.
• Don't use this tutorial as a programming guide but instead as a first step resource to get a brief exposure on the CRuntimeClass class.

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