Posts

Explicit Interface Implementation !!!

I have encountered this [wait i’ll explain] sort of situation many times and I mostly do this way in C++.

Assume you have a class CMyClass that exposes its functionality through its public methods, and also let it listen to events from some sources, events being OnSomeEvent or OnXXXX(), by implementing some event interface IXModuleEvents. Now these event listener methods are reserved only for internal use and are not meant to be called by the users. So when I implement the IXModuleEvents interface in CMyClass, I make them private. Think about it and the problem is solved. It is the polymorphism game, that never cares for the accessibility of the method.

The Interface Based Programming Argument !!!

I am always a great fan of interface programming. I mean not exactly the interface keyowrd but some way to expose the functionality of the class or your module relieving the user about the worries of the implementation. But definitely make him curious of the stuff inside.

The Win32 APIs are not that good in what I am talking about. Well, there are several reasons for that. And I strongly object that they are raw APIs and not for the ordinary application programmer. That kind of an abstraction is there at every level. Even a programmer using the Win32 APIs does not know what goes inside though some of the APIs expose unknowningly the sort of internals. This is an argument, but what I mean to say is that anything that you wish your users to use must have a elegant interface just exposing the functionality, and in the most intuitive way that makes sense. It may be an interface in C# or an abstract class in C++. And once you do that, you will slowly be under the tree where you can clearly realise the roots of an object oriented system.

Properties in C++/CLI - The C# look alike

Inherently after writing some code in C#, I wanted everything to be as easy to do like in C#. And could not resist myself writing property like syntax in C++ [ofcourse C++/CLI, threw away the ugly Managed C++ before it was too late for my code to grow into a tree]. Then I learnt that properties are supported in C++.NET too but as always in the ugly way. But in C++/CLI, I was happy enough that the syntax is more elegantly redefined. For instance, there was this boolean member logToStdError in my class, and in my legacy code, the property definition for logToStdError looked like:- More ...

Managed Debugging Assistant !!!

The Loader Lock is a synchronization object that helps to provide mutual exclusion during DLL loading and unloading. It helps to prevent DLLs being re-entered before they are completely initialized [in the DLLMain].

When some dll load code is executed, the loader lock is set and after the complete initialization it is unset. But there is a possibility of deadlock when threads do not properly synchronize on the loader lock. This mostly happens when threads try to call other Win32 APIs (LoadLibrary, GetProcAddress, FreeLibrary etc.) that also require the loader lock. Often this is evident in the mixed managed/unmanaged code, whereby it is not intentional but the CLR may have to call those APIs like during a call using platform invoke on one of the above listed Win32 API.

Do not delete [] a scalar pointer !!!

Recently I got tangled into this problem in my code - Calling a vector destructor for a scalar pointer. We all know that it is perfectly illegal to do that. For example, if we allocate something like this:-

OurClass *p = new OurClass();

and try to delete like this:-

delete []p;

then we are going to end up in trouble. Of course, we know that we will end up in trouble. But I have really not given a thought WHY!

Where do you QueryInterface ???

For an ATL class, the QueryInterface is implemented in CComObject. The figure below is the inheritance hierarchy for a class generated by the wizard representing an ATL-COM object.

CComObjectRootBase has an InternalQueryInterface method, which uses the interface map built by the BEGIN_COM_MAP macro to resolve IID -> interface pointer. The BEGIN_COM_MAP macro also defines a method _InternalQueryInterface, which passes the map on to InternalQueryInterface. CComObject implements QueryInterface, and calls _InternalQueryInterface.

Use Of Class Factories !!!

To understand quickly and to explain in the simplest way, Class Factories are the factory classes that create a COM object. A class factory may be responsible for creating one or more COM objects. In the case of COM OutOfProc servers, the server registers the class factories for objects that it can create in a system-global table using CoRegisterClassObject. Whenever a client does CoGetClassObject for a CLSID, the COM run-time can look it up in the system global table, and return the factory instance. The case with InProc servers is also similar but through the DLLGetClassObject. More ...

Unsafe Operations with STL !!!

It is UNSAFE to do any operation on an STL container that will modify its size while holding a reference to one of its existing element. What could happen is, when you do an operation, say push_back on a vector, it determines if there is enough space available to add a new element. If there is not sufficient space available, it allocates new space for whole of the data structure and deletes the old buffer. At this point, any reference to one of its elements created prior to push_back would have gotten corrupted. More ...

Consoles for Mr.GUI !!!

Learnt something new, a small one but very useful.

Many times I have seen GUI applications accompanied by console windows that show logs or trace information of the application. How do we do that for our application ?

Any GUI application can create its own console window just by calling AllocConsole Win32 API. Actually any process can use that API to allocate a new console. And the application must also learn to be disciplined enough to FreeConsole. Ok, fine. I used that in my small MFC application and was happy to see the console. But I did not see anything displayed on the console. As we know, each process has its own stdin, stdout and stderr. So redirect the console output of your parent application to the console. How do you do that ?

Setting Environment Variables !!!

Need to change or set the value of an environment variable programmatically and without the need to restart/log off the machine. I need the change to reflect for all processes, ie, I need to change the global environment value and not the one in the PEB [Process Environment Block] of a process. Frustated with setting the value of an environment variable !!!

For getting the set of environment variables or to get the value of an environment vaible from your C# program, there is the GetEnvironmentVariables/GetEnvironmentVariable API in the System.Environment class. But there is no API for setting the value of an environment variable.