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May 28, 2012
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If my window hosts multiple windowless ActiveX controls, which one do I call IOleInPlaceActiveObject::TranslateAccelerator and IOleInPlaceObjectWindowless::OnWindowMessage on?

Raymond Chen
Raymond Chen

Commenter Farproc asks how one goes about hosting two windowless ActiveX controls in a single window. In particular, "none of the documentation explains how to choose which control to send and on?" Actually, the documentation does say. The documentation for says, "Active in-place objects must always be given the first chance at translating ac...

Code
May 25, 2012
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The extern “C” specifier disables C++ mangling, but that doesn’t mean it disables mangling

Raymond Chen
Raymond Chen

The MSDN documentation on dllexport contains the following enigmatic paragraph, or at least did at the time I wrote this article: dllexport of a C++ function will expose the function with C++ name mangling. If C++ name mangling is not desired, either use a .def file (EXPORTS keyword) or declare the function as extern "C". I've seen this sente...

Code
May 24, 2012
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How do I prevent unchecked checkboxes in my listview control from disappearing?

Raymond Chen
Raymond Chen

A customer asked, "I have a listview control in report view with the extended style. I noticed that unchecked checkboxes are not visible until I hover over the corresponding item. Is it possible to get the checkboxes to be visible all the time?" I was kind of puzzled by this question because the default behavior of the list view control is to sho...

Code
May 23, 2012
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GUIDs are designed to be unique, not random

Raymond Chen
Raymond Chen

A customer liaison asked, "My customer is looking for information on the GUID generation algorithm. They need to select N items randomly from a pool of M (jury selection), and their proposed algorithm is to assign each item a GUID, then sort the items by GUID and take the first N." (I've seen similar questions regarding using GUIDs f...

Code
May 11, 2012
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When you crash on a mov ebx, eax instruction, there aren't too many obvious explanations, so just try what you can

Raymond Chen
Raymond Chen

A computer running some tests encountered a mysterious crash: A colleague of mine quickly diagnosed the proximate cause. *Something* marked the code page PAGE_READWRITE, instead of PAGE_EXECUTE_READ. I suspect a bug in a driver. FOO is just a victim here. This diagnosis was met with astonishment. "Wow! What made you think to check the pr...

Code
May 9, 2012
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How do I hide a window without blocking on it?

Raymond Chen
Raymond Chen

A customer was working on improving their application startup performance. They found that if their application was launched immediately after a fresh boot, the act of dismissing their splash screen was taking over 5% of their boot time. Their code removed the splash screen by calling . They suspect that the splash screen thread has, for some reaso...

Code
May 4, 2012
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How does the MultiByteToWideChar function treat invalid characters?

Raymond Chen
Raymond Chen

The flag controls how the function treats invalid characters. Some people claim that the following sentences in the documentation are contradictory: "Starting with Windows Vista, the function does not drop illegal code points if the application does not set the flag." "Windows XP: If this flag is not set, the function silently drops il...

Code
Apr 27, 2012
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A process shutdown puzzle, Episode 2

Raymond Chen
Raymond Chen

A customer reported that their program would very sporadically crash in the function . The customer was kind enough to provide a stack trace at the point of the crash: The customer wondered, "Could the problem be that my cleanup group does not have a callback? MSDN seems to suggest that this is okay." The exception being thrown is , but that...

Code
Apr 20, 2012
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What does INIT_ONCE_CTX_RESERVED_BITS mean?

Raymond Chen
Raymond Chen

Windows Vista adds the One-Time Initialization family of functions which address a common coding pattern: I want a specific chunk of code to run exactly once, even in the face of multiple calls from different threads. There are many implementations of this pattern, such as the infamous double-checked lock. The double-checked lock is very easy to...

Code
Apr 16, 2012
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Why do we need IsDialogMessage at all?

Raymond Chen
Raymond Chen

alv wonders why we need the function at all. "All its activity could take place inside the window procedure of the modeless dialog itself", since when it doesn't have focus, it shouldn't be responding to messages anyway. Sure, that works great if the modeless dialog has focus. But it almost never does. What has focus is a control inside the mode...

Code