The Old New Thing

Enumerating bit strings with a specific number of bits set (binomial coefficients strike again)

June 16, 2014 Jun 16, 2014 06/16/14

Raymond Chen

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 ...

Non-classical processor behavior: How doing something can be faster than not doing it

June 13, 2014 Jun 13, 2014 06/13/14

Raymond Chen

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 ...

Can we continue to call FindNextFile() with the same handle that returned an error last time?

June 12, 2014 Jun 12, 2014 06/12/14

Raymond Chen

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 ...

Improving the performance of CF_HDROP by providing file attribute information

June 9, 2014 Jun 9, 2014 06/9/14

Raymond Chen

The clipboard format is still quite popular, despite its limitation of being limited to files. You can't use it to represent virtual content, for example. For all of you still using , you can improve the performance of drag/drop operations by adding a little more information to your data object. Observe that the clipboard format is ...

Closing over the loop variable is just as harmful in JavaScript as it is in C#, and more cumbersome to fix

June 5, 2014 Jun 5, 2014 06/5/14

Raymond Chen

Prerequisite reading: Closing over the loop variable considered harmful. JavaScript has the same problem. Consider: The most common case where you encounter this is when you are hooking up event handlers in a loop, so that's the case I used as an example. No matter which button you click, they all alert , rather than the respective ...

Obtaining information about the user's wallpaper on multiple monitors

June 2, 2014 Jun 2, 2014 06/2/14

Raymond Chen

Today we're going to dump information about the user's wallpaper settings on multiple monitors. The idea is simple. You use the interface on the object to get information about the desktop wallpaper. It will tell you the wallpaper positioning information, whether a single image is being used for all monitors, where those monitors are, and...

Why does GetFileVersionInfo map the whole image into memory instead of just parsing out the pieces it needs?

May 30, 2014 May 30, 2014 05/30/14

Raymond Chen

Commenter acq responds (with expletive deleted), "the whole file is mapped into the process' memory only for version info that's certainly only a few kilobytes to be read?" Why not map only the parts that are needed? "I don't understand the necessity to map the whole file except that it was easier to write that code without thinking too much...

Find the index of the smallest element in a JavaScript array

May 26, 2014 May 26, 2014 05/26/14

Raymond Chen

Today's Little Program isn't even a program. It's just a function. The problem statement is as follows: Given a nonempty JavaScript array of numbers, find the index of the smallest value. (If the smallest value appears more than once, then any such index is acceptable.) One solution is simply to do the operation manually, simulating how ...

Why is the debugger telling me I crashed because my DLL was unloaded, when I see it loaded right here happily executing code?

May 23, 2014 May 23, 2014 05/23/14

Raymond Chen

A customer was puzzled by what appeared to be contradictory information coming from the debugger. We have Windows Error Reporting failures that tell us that we are executing code in our DLL which has been unloaded. Here's a sample stack: But if we ask the debugger what modules are loaded, our DLL is right there, loaded as happy as can ...