The Old New Thing

Why does my radio button group selection get reset each time my window regains activation?

May 22, 2014 May 22, 2014 05/22/14

Raymond Chen

A customer reported (all incomplete information and red herrings preserved): We have an issue related to two radio buttons in a window. The code programmatically checks the second button by sending the message. We observe that if the user clicks somewhere else on the screen (so that our application loses focus), and then clicks on the ...

Dialog boxes return focus to the control that had focus when you last switched away; how do I get in on that action for my own windows?

May 21, 2014 May 21, 2014 05/21/14

Raymond Chen

You start typing.

Creating a simple shell item, just as fake as a simple pidl

May 19, 2014 May 19, 2014 05/19/14

Raymond Chen

Continuing from Creating a simple pidl: For the times you care enough to send the very fake: Instead of creating a simple pidl, we'll create a simple shell item. The idea is the same. We build a file system bind context containing the information about the fake file, and we pass that bind context to the function. Take that program that ...

An extensible interlocked arithmetic function (via lambdas)

May 16, 2014 May 16, 2014 05/16/14

Raymond Chen

Some time ago, I noted that you can build other interlocked operations out of . Here's an example: (There's a corresponding C++ version, which I leave as an exercise.) This function atomically updates a "highest value seen so far" variable. It follows the usual pattern: Capture the starting value. Do a computation based on that value...

Is WriteProcessMemory atomic?

May 15, 2014 May 15, 2014 05/15/14

Raymond Chen

How could it be?

The mystery of the icon that never appears

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

Raymond Chen

A customer reported a problem showing an icon on their dialog box. We verified that this code does execute during the handling of the message. No assertion fires, yet no icon appears either. Our dialog template says The customer did some helpful preliminary troubleshooting: Verify that the code does indeed execute. It sounds ...

Enumerating bit sequences with isolated zero-bits via the Fibonacci recurrence

May 12, 2014 May 12, 2014 05/12/14

Raymond Chen

Today's Little Program enumerates bit sequences of a particular length subject to the constraint that you cannot have consecutive 0-bits. This may sound kind of arbitrary, but it is important in magnetic media storage, because you cannot go too long without a flux reversal (traditionally represented by a 1); otherwise, the read head's clock ...

How can you use both versions 5 and 6 of the common controls within the same module?

May 8, 2014 May 8, 2014 05/8/14

Raymond Chen

Commenter Medinoc was baffled by the statement that the decision to use the visual-styles-enabled version of the common controls library is done on a window-by-window basis. " Isn't it rather on a per-module basis, depending on each module's manifest? If it is indeed on a per-window basis, how does one choose?" Whether a particular call to...

Why does saving a file in Notepad fire multiple FindFirstChangeNotification events?

May 7, 2014 May 7, 2014 05/7/14

Raymond Chen

Many people have noticed that the and functions (and therefore their BCL equivalent and WinRT equivalent ) fire multiple events when you save a file in Notepad. Why is that? Because multiple things were modified. Notepad opens the file for writing, writes the new data, calls to truncate any excess data (in case the new file is shorter ...

Getting the location of the Close button in the title bar

May 5, 2014 May 5, 2014 05/5/14

Raymond Chen

Today's Little Program locates the × button in the corner of the window and, just to show that it found it, displays a balloon tip pointing at it. Let's start with the program from last week, the one that displays a balloon tip, then make these changes: Instead of positioning the balloon at the cursor position, we put it at the ...