October 2010 | Page 2 of 3 | The Old New Thing

The evolution of the ICO file format, part 2: Now in color!

Raymond ChenOctober 19, 2010Oct 19, 201010/19/10

Last time, we looked at the format of classic monochrome icons. But if you want to include color images, too? (Note that it is legal—and for a time it was common—for a single ICO file to offer both monochrome and color icons. After all, a single ICO file can offer both 16-color and high-color images; why not also 2-color images?)

The evolution of the ICO file format, part 1: Monochrome beginnings

Raymond ChenOctober 18, 2010Oct 18, 201010/18/10

This week is devoted to the evolution of the ICO file format. Note that the icon resource format is different from the ICO file format; I'll save that topic for another day. The ICO file begins with a fixed header: idReserved must be zero, and idType must be 1. The idCount describes how many images are included in this ICO file. An ICO f

What does the FOF_NOCOPYSECURITYATTRIBS flag really do (or not do)?

Raymond ChenOctober 15, 2010Oct 15, 201010/15/10

In the old days, the shell copy engine didn't pay attention to ACLs. It just let the file system do whatever the default file system behavior was. The result was something like this: Perfectly logical, right? If a new file is created, then the security attributes are inherited from the container. If an existing file is moved, then its secur

The memcmp function reports the result of the comparison at the point of the first difference, but it can still read past that point

Raymond ChenOctober 14, 2010Oct 14, 201010/14/10

This story originally involved a more complex data structure, but that would have required too much explaining (with relatively little benefit since the data structure was not related to the moral of the story), so I'm going to retell it with double null-terminated strings as the data structure instead. Consider the following code to compa

How do I get the color depth of the screen?

Raymond ChenOctober 13, 2010Oct 13, 201010/13/10

How do I get the color depth of the screen? This question already makes an assumption that isn't always true, but we'll answer the question first, then discuss why the answer is wrong. If you have a device context for the screen, you can query the color depth with a simple arithmetic calculation: Now that you have the answer, I'll explai

Why are the keyboard scan codes for digits off by one?

Raymond ChenOctober 12, 2010Oct 12, 201010/12/10

In Off by one what, exactly?, my colleague Michael Kaplan wrote And this decision long ago that caused the scan codes to not line up for these digits when they could have... The word that struck me there was "decision". Because it wasn't a "decision" to make the scan codes almost-but-not-quite line up with digits. It was just a coincid

Why does each drive have its own current directory?

Raymond ChenOctober 11, 2010Oct 11, 201010/11/10

Commenter Dean Earley asks, "Why is there a 'current directory' AND an current drive? Why not merge them?" Pithy answer: Originally, each drive had its own current directory, but now they don't, but it looks like they do. Okay, let's unwrap that sentence. You actually know enough to answer the question yourself; you just have to put the p

Why does TaskDialog return immediately without showing a dialog? – Answer

Raymond ChenOctober 8, 2010Oct 8, 201010/8/10

Last time, I left an exercise to determine why the TaskDialog function was not actually displaying anything. The problem had nothing to do with an invalid window handle parameter and had all to do with original window being destroyed. My psychic powers told me that the window's WM_DESTROY handler called PostQuitMessage. As we

Why does my asynchronous I/O request return TRUE instead of failing with ERROR_IO_PENDING?

Raymond ChenOctober 8, 2010Oct 8, 201010/8/10

A customer reported that their program was not respecting the FILE_FLAG_OVERLAPPED flag consistently: My program opens a file handle in FILE_FLAG_OVERLAPPED mode, binds it to an I/O completion callback function with BindIoCompletionCallback, and then issues a WriteFile against it. I would expect that the WriteFile ret

The overlooked computer room at school that became my "office" for a while

Raymond ChenOctober 7, 2010Oct 7, 201010/7/10

VIMH's comment on an unmarked restroom that is largely unknown reminds me of a story from my college days. Since my final project involved computational geometry, I was granted a key to the rooms in our department which had the computers with fancy graphical displays. (The term "fancy graphical display" is a relative one, mind you. By today'

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