The Old New Thing

Code - The Old New Thing

If an asynchronous I/O completes synchronously, is the hEvent in the OVERLAPPED structure signaled anyway?

February 6, 2014 Feb 6, 2014 02/6/14
Raymond Chen
Yes. When an I/O completes (whether synchronously or asynchronously), the event is signaled and completion status notifications are queued. The function can be used to wait on an I/O that has already completed; it will merely return immediately. If you ask whether the I/O has completed, and the I/O completed synchronously, it will correctly...

How can I make a WNDPROC or DLGPROC a member of my C++ class?

February 3, 2014 Feb 3, 2014 02/3/14
Raymond Chen
Continuing my discussion of How can I make a callback function a member of my C++ class? Common special cases for wanting to use a member function as a callback function are the window procedure and its cousin the dialog procedure. The question, then, is where to put the reference data. Let's start with window procedures. The function ...

Non-psychic debugging: If somebody's complaining that a collection should be empty but isn't, you might want to see what's in there

January 31, 2014 Jan 31, 2014 01/31/14
Raymond Chen
A programmer on the GHI team (yes, the same GHI team) reported that they were hitting an assertion failure using an internal library and asked for help debugging it. "Can somebody help me figure out which factory it is that did not get unregistered?" I didn't work on this internal library, but on the other hand I'm not afraid to look ...

One of my favorite error codes: Optional parameter missing

January 29, 2014 Jan 29, 2014 01/29/14
Raymond Chen
The error Optional parameter missing sounds awfully paradoxical, doesn't it. I mean, if the parameter is optional, why are you complaining that it's missing? This KB article explains why, specifically, the part that says, "If a parameter is omitted, the calling program must…". For those who don't want to click through, here's the ...

How can I make a callback function a member of my C++ class?

January 27, 2014 Jan 27, 2014 01/27/14
Raymond Chen
Instead of a Little Program today, I'm going to answer a Little Question. This is a common beginner question, but I figure I'll just spell it out right here for posterity. First of all, you probably noticed that you can't do this: That's because the is declared as a so-called free function, but member functions are not free. Neither are...

Non-psychic debugging: Looking for leaked objects by their vtable

January 24, 2014 Jan 24, 2014 01/24/14
Raymond Chen
A programmer on the GHI team reported that they were hitting an assertion failure using an internal library and asked for help debugging it. I didn't work on this internal library, but on the other hand I'm also not afraid to look inside and around. The assertion failure said, "Assertion failed: All widgets from a factory must be ...

What clock do MSG.time and GetMessageTime use?

January 22, 2014 Jan 22, 2014 01/22/14
Raymond Chen
The structure has a field called which is a . There is also a function which returns a . Both are documented as returning the time the message was generated, but the types are different. Are these time units comparable? Yes, they are the same thing. They all use the 32-bit timer provided by the function. Sorry about the inconsistency in...

How do I get a high resolution icon for a file?

January 20, 2014 Jan 20, 2014 01/20/14
Raymond Chen
Today's Little Program obtains a high resolution icon for a file. Start with our scratch program and make these changes. Remember, Little Programs do little or no error checking. This week's smart pointer class is (rolls dice) ! The function does nothing new. It simply retrieves the system image list icon index for a file's icon. The...