The Old New Thing

How do the common controls convert between ANSI and Unicode?

June 16, 2008 Jun 16, 2008 06/16/08

Raymond Chen

Commenter Chris Becke asks how the common controls convert ANSI parameters to Unicode, since the common controls are Unicode internally. Everything goes through , pretty much by definition. The ANSI code page is . That's what ACP stands for, after all. Now, there are some function families that do not use ANSI. The console subsystem, for ...

If you say that you don't care about something, you shouldn't be upset that it contains garbage

June 11, 2008 Jun 11, 2008 06/11/08

Raymond Chen

There are many situations where you pass a structure to a function, and the function fills in the structure with information you request. In some cases, the function always fills in the entire structure (example: ). In other cases, you tell the function which bits of information you care about, to save the function the effort of computing ...

Why are DLLs uninitialized in the "wrong" order?

June 9, 2008 Jun 9, 2008 06/9/08

Raymond Chen

This is really just a corollary to Why are DLLs unloaded in the "wrong" order. Exactly the same logic that explains why DLLs are unloaded in the "wrong" order also explains why they are uninitialized in the "wrong" order. Once you understand the first issue, the second comes for free; just change to in your analysis. Apply the logic to ...

Why does OpenProcess succeed even when I add three to the process ID?

June 6, 2008 Jun 6, 2008 06/6/08

Raymond Chen

A customer noticed that if you add three to a process ID and pass it to the function, it still succeeds. Why is that? Well, first of all, I need to say up front that the behavior you're seeing is an artifact of the implementation and is not part of the contract. You're passing intentionally invalid parameters, what did you expect? The ...

Why are accelerators for hidden controls still active?

June 2, 2008 Jun 2, 2008 06/2/08

Raymond Chen

In the suggestion box, Serge Wautier asked why accelerators for hidden controls remain active. He's apparently rather insistent because he asked the question again a few months later. Asking the same question multiple times reduces the likelihood that I'll answer it. Consider yourself lucky that I wrote this answer before I noticed the ...

Reading a contract from the other side: SHSetInstanceExplorer and SHGetInstanceExplorer

May 28, 2008 May 28, 2008 05/28/08

Raymond Chen

Shell extensions that create worker threads need to call the function so that Explorer will not exit while the worker thread is still running. When your worker thread finishes, you release the that you obtained to tell the host program, "Okay, I'm done now, thanks for waiting." You can read this contract from the other side. Instead of ...

You can't give away something that isn't yours

May 27, 2008 May 27, 2008 05/27/08

Raymond Chen

This rule of real life applies to code as well. If something doesn't belong to you, then you can't give it away. For example, functions like and take ownership of the item that you pass it. In SetClipboardData's case, the memory block you pass as the parameter becomes the property of the clipboard. For it's the that becomes the ...

What does TranslateAccelerator do?

May 23, 2008 May 23, 2008 05/23/08

Raymond Chen

For some reason, there appears to be some confusion over what does. It's very simple, and it's all spelled out in the documentation. You give it a message, and if the message is a keypress that matches an entry in the accelerator table, the corresponding or message is sent to the window you said you are translating messages for. One ...

The Phantom Bug: Why doesn't MessageBox work from my WM_NCDESTROY handler?

May 20, 2008 May 20, 2008 05/20/08

Raymond Chen

Adrian McCarthy ran into a problem where didn't work when called from a handler. You already know how to solve this; you just have to connect the dots. See if you can do it on your own before the answer is revealed...

How do I flash my window caption and taskbar button manually?

May 12, 2008 May 12, 2008 05/12/08

Raymond Chen

Commenter Jonathan Scheepers wonders about those programs that flash their taskbar button indefinitely, overriding the default flash count set by . The function and its simpler precursor let a program flash its window caption and taskbar button manually. The window manager flashes the caption automatically (and Explorer follows the ...