The Old New Thing

The correct order for disabling and enabling windows

If you want to display modal UI, you need to disable the owner and enable the modal child, and then reverse the procedure when the modal child is finished. And if you do it wrong, focus will get all messed up. If you are finished with a modal dialog, your temptation would be to clean up in the following order: But if you do that, ...
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What's so special about the desktop window?

The window returned by GetDesktopWindow() is very special, and I see people abusing it all over the place. For example, many functions in the shell accept a window handle parameter to be used in case UI is needed. IShellFolder::EnumObjects, for example. What happens if you pass GetDesktopWindow()? If UI does indeed need to be ...
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Invalid thread and process IDs

Perhaps you want a value to use as a sentinel, which you want to be guaranteed is never a valid thread ID or process ID. What values can you use? Nothing is explicitly written about this topic, but you can put on your logic cap and figure it out. If you need an invalid thread ID, you can use zero. How do you know that zero is an ...
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Why do I get a QueryInterface(IID_IMarshal) and then nothing?

A common problem when trying to get your new COM object off the ground is that you can't seem to be able to get it created. The object comes out of the class factory, and it gets a QueryInterface for IMarshal, and then nothing. What's going on? This is a sure sign that you didn't register your CLSID properly; most likely you forgot to ...
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Answer to exercise: Pointer to member function cast

Yesterday's exercise asked you to predict and explain the codegen for the following fragment: Well, the codegen might go something like this: Let's use one of our fancy pictures: Just for fun, I swapped the order of Base1 and Base2. There is no requirement in the standard about the order in which storage is allocated for base classes...
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Pointers to member functions are very strange animals

Pointers to member functions are very strange animals. Warning: The discussion that follows is specific to the way pointers to member functions are implemented by the Microsoft Visual C++ compiler. Other compilers may do things differently. Well, okay, if you only use single inheritance, then pointers to member functions are just a ...
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Answers to exercises – mismatching new/delete

Answers to yesterday's exercises: What happens if you allocate with scalar "new" and free with vector "delete[]"? The scalar "new" will allocate a single object with no hidden counter. The vector "delete[]" will look for the hidden counter, which isn't there, so it will either crash (accessing nonexistent memory) or grab a random number ...
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Mismatching scalar and vector new and delete

In a previous entry I alluded to the problems that can occur if you mismatch scalar "new" with vector "delete[]" or vice versa. There is a nice description of C++ memory management in C++ Gotchas: Avoiding Common Problems in Coding and Design on www.informit.com, and I encourage you to read at least the section titled Failure to ...
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