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Continuing from yesterday, here's another case where you have to watch your destructors. Yesterday's theme was destructors that run at the wrong time. Today, we're going to see destructors that don't run at all! Assume there's an ObjectLock class which takes a lock in its constructor and releases it in its destructor. Pretty standard stuff. Th...

Larry Osterman discussed the importance of knowing when your global destructors run, but this problem is not exclusive to global objects. You need to take care even with local objects. Consider: Easy as pie. And there's a bug here. When does the destructor for that smart-pointer run? Answer: When the object goes out of scope, which is a...

Just because you have the ASCII table memorized doesn't mean you know how sorting works. I remember a bug filed where somebody said that the "sort" command was sorting underscores incorrectly: this was claimed to be wrong "because underscore character follow uppercase letters and precedes lowercase letters". Well perhaps it does if you thi...

There have been a few good articles about threading models, one from Eric Lippert and another from Larry Osterman. Go off and read them if you haven't already.

It's really not that complicated. If you permit, say, , then you're saying, "I'm okay with other people reading this file while I have it open." And if you leave off the flag, then you're saying, "I do not want other people reading this file while I have it open." Now all that's left to do is work out what that means. So suppose you omit t...

Remember that there are two types of scrollbars. One is the standalone scrollbar control. This one has its own window handle, and consequently can be given focus and all those other fun things you can do with window handles. To manipulate them, pass the handle to the scrollbar control to the appropriate scrollbar function (SetScrollInfo, fo...

When should your C++ object's destructor be virtual? First of all, what does it mean to have a virtual destructor? Well, what does it mean to have a virtual method? If a method is virtual, then calling the method on an object always invokes the method as implemented by the most heavily derived class. If the method is not virtual, then the implem...

Back in Windows 95, people would notice that their hard drive light would blink every few seconds. What's that all about? Actually, it wasn't the hard drive light after all. Windows 95 was polling your CD-ROM drive to see whether you had inserted a new CD. Some computers wired up the "hard drive light" not to the hard drive but r...

Both C++ and C# have the concept of virtual functions. These are functions which always invoke the most heavily derived implementation, even if called from a pointer to the base class. However, the two languages differ on the semantics of virtual functions during object construction and destruction. C# objects exist as their final type before co...

Microsoft Active Accessibilty is the technology that exposes information about objects on the screen to accessibility aids such as screen readers. But that doesn't mean that only screen readers can use it. Here's a program that illustrates the use of Active Accessibility at the most rudimentary level: Reading text. There's much more to Active ...