The Old New Thing
Practical development throughout the evolution of Windows.
Latest posts
Adding a sound to the Alt+Tab window
Today's Little Program plays a sound when the Alt+Tab window appears and disappears. The program registers an accessibility event hook for the and events. The Start event fires when an Alt+Tab operation begins, and the End event fires when an Alt+Tab operation completes. As noted in the documentation, you can get spurious End events, so we keep track of our current state to avoid any surprises. In addition to adding an annoying sound to the Alt+Tab window, let's also add an annoying sound each time you move focus to a new item. Okay, this was a pretty annoying program, but maybe you can use it for som...
Once you go input-idle, your application is deemed ready to receive DDE messages
Feel free to stop using DDE. There was one customer who confessed that they were still using DDE, and they asked for help debugging a DDE problem. They found that sometimes, when their application was launched for DDE, it never received the message. Instead, the function returned . If launched from Explorer, the error message shown to the user was "There was a problem sending the command to the program." It took a long time to figure out what was going on, and there were a number of dead ends, but I'll cut to the chase: The problem was that one of the features they added to their program included code that r...
What happened to the Shut Down menu in classic Task Manager?
The great thing about open comments is that anybody can use them to introduce their favorite gripe as long as it shares at least four letters of the alphabet in common with the putative topic of the base article. xpclient "asks" why the Shut Down menu was removed from Task Manager. I put the word "asks" in quotation marks, because it's really a complaint disguised as a question. As in "Why do you guys suck?" The first thing to understand is that classic Task Manager went into a state of sustained engineering since Windows 2000. In other words, the component is there, but there is no serious interest in i...
10 is the new 6
While it may no longer be true that everything at Microsoft is built using various flavors of Visual C++ 5.0, 6.0, and 7.0, there is still a kernel of truth in it: A lot of customers are still using Visual C++ 6.0. That's why the unofficial slogan for Visual C++ 2010 was 10 is the new 6. Everybody on the team got a T-shirt with the slogan (because you don't have a product until you have a T-shirt).
Who would ever write a multi-threaded GUI program?
During the development of Windows 95, the user interface team discovered that a component provided by another team didn't work well under multi-threaded conditions. It was documented that the function had to be the first call made by a thread into the component. The user interface team discovered that if one thread called , and then used the component, then everything worked great. But if a second thread called , the component crashed whenever the second thread tried to use it. The user interface team reported this bug back to the team that provided the component, and some time later, an updated version o...
Enumerating bit strings with a specific number of bits set (binomial coefficients strike again)
Today's Little Program prints all bit strings of length n subject to the requirement that the string have exactly k 1-bits. For example, all bit strings of length 4 with 2 bits set are 0011, 0101, 0110, 1001, 1010, and 1100. Let's write BitString(n, k) to mean all the bit strings of length n with exactly k bits set. Let's look at the last bit of a typical member of BitString(n, k). If it is a zero, then removing it leaves a string one bit shorter but with the same number of bits set. Conversely every BitString(n − 1, k) string can be extended to a BitString(n, k) string by adding a zero to the end. ...
Non-classical processor behavior: How doing something can be faster than not doing it
Consider the following program: The program generates a lot of random integers in the range 0..9 and then counts how many are less than 0, less than 1, less than 2, and so on. It also prints how long the operation took in QPC units. We don't really care how big a QPC unit is; we're just interested in the relative values. (We print the number of items found merely to verify that the result is close to the expected value of .) Here are the results: To the untrained eye, this chart is strange. Here's the naïve analysis: When the boundary is zero, there is no incrementing at all, so the entire running...
Can we continue to call FindNextFile() with the same handle that returned an error last time?
A customer wanted to know whether it was okay to call with the same handle that returned an error last time. In other words, consider the following sequence of events: The customer elaborated: Suppose that the directory contains four files, A, B, C, and D. We expect the following: After returns an error, can we continue to search with the same handle? Or should we close the handle and get a new one from ? If it depends on the type of error that occurred, the customer would like to know more details about when the search can be continued and when it cannot. We asked the customer what problem they're ...
Why do network servers sometimes show up as a Recycle Bin Location?
A customer wanted to know why some of their users showed network servers among the locations shown in the Recycle Bin property sheet. Answer: Because those users are using Folder Redirection. In particular, if you redirect the My Documents folder, then a network Recycle Bin location is created to hold the files deleted from My Documents. The Recycle Bin folder in the user interface shows the union of all the recycled files in the individual Recycle Bin locations.