The Old New Thing

How can I tell that a directory is really a recycle bin?

September 18, 2008 Sep 18, 2008 09/18/08

Raymond Chen

Here's a question inspired by an actual customer question: I need a function that, given a path, tells me whether it is a Recycle Bin folder. I tried using functions like SHGetSpecialFolderPath with CSIDL_BITBUCKET, but that doesn't work because the Recycle Bin is a virtual folder that is the union of the Recycle Bins of all drives. The ...

Who is responsible for destroying the font passed in the WM_SETFONT message?

September 12, 2008 Sep 12, 2008 09/12/08

Raymond Chen

The message tells a control which font you would like the control to use for its text. This message is a convention, not a rule. For example, our scratch program doesn't pay attention to the message. If somebody sends it a , nothing happens. The scratch program just ignores the caller and uses whatever font it wants. Although supporting ...

How do I convert an error code to text when FORMAT_MESSAGE_FROM_SYSTEM doesn’t work?

September 1, 2008 Sep 1, 2008 09/1/08

Raymond Chen

For the same reason that not all error codes are defined in , not all error strings are defined in the system message table. If you've ever played with the message compiler, you'd quickly have recognized the file as the header file associated with a message resource. In other words, there's a file that gets processed by the message ...

What possible use are those extra bits in kernel handles? Part 3: New object types

August 29, 2008 Aug 29, 2008 08/29/08

Raymond Chen

Last time, we saw how those extra bits can be used to multiplex HANDLE with other values. That was a specific case of a more general scenario: Expanding the handle namespace to include things that aren't handles. (You can also view today's example as a generalization of the sentinel value problem, where we need to generate an arbitrary ...

What possible use are those extra bits in kernel handles? Part 2: Overcoming limited expressiveness

August 28, 2008 Aug 28, 2008 08/28/08

Raymond Chen

Last time, we saw how those extra bits can be used to develop safe sentinel values. That is a special case of a more general problem: How do you pack 33 bits of information into a 32-bit value? Whereas last time, we weren't forced into the use of a sentinel value because we could develop a (cumbersome) helper class and switch people ...

What possible use are those extra bits in kernel handles? Part 1: Sentinels

August 27, 2008 Aug 27, 2008 08/27/08

Raymond Chen

Kernel handles are always a multiple of four; the bottom two bits are available for applications to use. But why would an application need those bits anyway? The short answer is extending the handle namespace. The long answer will take a few days to play out. (This series was written in response to Igor Levicki being unable to imagine "...

The implementation of iterators in C# and its consequences (part 4)

August 15, 2008 Aug 15, 2008 08/15/08

Raymond Chen

You can breathe a sigh of relief. Our long national nightmare is over: this is the end of CLR Week 2008. We wind down with a look back at iterators. Michael Entin points out that you can use C# iterators to make asynchronous code easier to write. You can use C# iterators for more than simply iterating. The automatic ...

The implementation of iterators in C# and its consequences (part 3)

August 14, 2008 Aug 14, 2008 08/14/08

Raymond Chen

I mentioned that there was an exception to the general statement that the conversion of an iterator into traditional C# code is something you could have done yourself. That's true, and it was also a pun, because the exception is exception handling. If you have a try ... finally block in your iterator, the language executes the finally ...

The implementation of iterators in C# and its consequences (part 2)

August 13, 2008 Aug 13, 2008 08/13/08

Raymond Chen

Now that you have the basic idea behind iterators under your belt, you can already answer some questions on iterator usage. Here's a scenario based on actual events: I have an iterator that is rather long and complicated, so I'd like to refactor it. For illustrative purposes, let's say that the enumerator counts from 1 to 100 twice. (In ...

The implementation of iterators in C# and its consequences (part 1)

August 12, 2008 Aug 12, 2008 08/12/08

Raymond Chen

Like anonymous methods, iterators in C# are very complex syntactic sugar. You could do it all yourself (after all, you did have to do it all yourself in earlier versions of C#), but the compiler transformation makes for much greater convenience. The idea behind iterators is that they take a function with yield return statements (and ...