The Old New Thing

March 2014 - The Old New Thing

A puzzle involving dynamic programming, or maybe it doesn't

March 31, 2014 Mar 31, 2014 03/31/14
Raymond Chen
Here's a programming challenge: Evaluate the following recurrence relation efficiently for a given array [x0, …, xn−1] and integer k. Hint: Use dynamic programming. In words: If the array has only two elements, then the result is the average of the two elements. If the array has more than two elements, then ...

The dangers of buffering up posted messages and then reposting them later

March 28, 2014 Mar 28, 2014 03/28/14
Raymond Chen
A customer wanted to check that their idea for solving a re-entrancy problem doesn't have any hidden gotchas. We have a window which processes incoming work. One of our work items enters a modal loop, and if new work gets posted to the window while the modal loop is running, our work manager gets re-entered, and Bad Things happen. Our ...

Functions that return GDI regions rarely actually return regions

March 27, 2014 Mar 27, 2014 03/27/14
Raymond Chen
For reasons I don't quite understand, the only functions in GDI and USER which create GDI regions are the functions with in their name, like or . All the other functions which return a region require you to pass an existing region to use as the output. I can see this being useful for , because you can set your output region to be equal to...

Can CoCreateGuid ever return GUID_NULL?

March 26, 2014 Mar 26, 2014 03/26/14
Raymond Chen
A customer asked whether the function can ever return . Their code uses for special purposes, and it would be bad if that was ever returned as the GUID for an object. "Can we assume that never returns ? Or should we test the return value against , and if it is equal, then call and try again?" Some people started running a bunch of times ...

Geeky t-shirt alert: Windows 7's so-called God Mode

March 25, 2014 Mar 25, 2014 03/25/14
Raymond Chen
Back in 2010, the so-called God Mode was the hit discovery of the Internet, at least until the next cute cat video made the rounds. If you had stopped by the Microsoft Visitor Center during that meme's brief moment in the sun, and wandered into the gift shop, you could have picked up a t-shirt that said on the front. Of course, if you ...

Different senses of scale create different travel expectations

March 21, 2014 Mar 21, 2014 03/21/14
Raymond Chen
A friend of mine had a business meeting near London, and he decided to extend it to a tour of Scotland and England once the meetings were over. (This is the same friend who took me on the emergency vacation many years ago.) His plan was to rent a car early one morning and drive from the meeting location all the way up to Aberdeen at one go, ...

Going for the facts: Who is displaying this message box?

March 20, 2014 Mar 20, 2014 03/20/14
Raymond Chen
A customer wanted to know whether had a problem with Unicode. A problem with it? Quite the contrary. loves Unicode! In fact, if you call the ANSI version, it converts the strings to Unicode and then finishes the work in Unicode. Okay, here's the customer's problem. We have a custom application written in managed code. When we launch ...