The Old New Thing

Why are the alignment requirements for SLIST_ENTRY so different on 64-bit Windows?

August 19, 2011 Aug 19, 2011 08/19/11

Raymond Chen

The function stipulates that all list items must be aligned on a boundary. For 32-bit Windows, is 8, but the structure itself does not have a attribute. Even more confusingly, the documentation for says that the 64-bit structure needs to be 16-byte aligned but says nothing about the 32-bit structure. So what are the memory ...

ReadDirectoryChangesW reads directory changes, but what if the directory doesn't change?

August 12, 2011 Aug 12, 2011 08/12/11

Raymond Chen

The function reads changes to a directory. But not all changes that happen to files in a directory result in changes to the directory. Now, it so happens that nearly all changes to a file in a directory really do result in something happening to the file's directory entry. If you write to a file, the last-write time in the directory entry ...

The ways people mess up IUnknown::QueryInterface, episode 4

August 11, 2011 Aug 11, 2011 08/11/11

Raymond Chen

One of the rules for is so obvious that nobody even bothers to state it explicitly as a rule: "If somebody asks you for an interface, and you return , then the pointer you return must point to the interface the caller requested." (This feels like the software version of dumb warning labels.) During compatibility testing for Windows ...

What does the CreateProcess function do if there is no space between the program name and the arguments?

August 8, 2011 Aug 8, 2011 08/8/11

Raymond Chen

In an old discussion of why the function modifies its command line, commenter Random832 asked, "What if there is no space between the program name and arguments - like "cmd/?" - where does it put the null then?" The function requires a space between the program name and arguments. If you leave out the space, then the arguments are ...

Why doesn't b match word boundaries correctly?

August 4, 2011 Aug 4, 2011 08/4/11

Raymond Chen

A colleague of mine was having trouble getting the metacharacter in a regular expression to work. Of course, when somebody asks a question like that, you first have to establish what their definition of "work" is. Fortunately, he provided some examples: "The last two entries are just sanity checks to make sure I didn't make some stupid ...

A shell extension is a guest in someone else's house; don't go changing the code page

August 3, 2011 Aug 3, 2011 08/3/11

Raymond Chen

A customer reported a problem with their shell extension: We want to format a floating point number according to the user's default locale. We do this by calling to convert the value from floating point to text with a period (U+002E) as the decimal separator, then using to apply the user's preferred grouping character, decimal separator, ...

Simulating input via WM_CHAR messages may fake out the recipient but it won't fake out the input system

July 28, 2011 Jul 28, 2011 07/28/11

Raymond Chen

We saw some time ago that you can't simulate keyboard input with . You may get away with it, depending on how the application you're trying to fake out processes input, but since you're just faking data, the application may discover that it's all a ruse when they try to access information that you didn't fake out, say by calling and ...

You don't need to ask me a question the compiler can answer more accurately

July 27, 2011 Jul 27, 2011 07/27/11

Raymond Chen

A customer reported having problems developing the correct p/invoke signature for the structure. "The code works on 32-bit machines, but on 64-bit machines, the call to returns ." The sample code included the lines My response was simply, "I bet you are passing the wrong structure size. Note that on 64-bit Windows, the alignment of the...

How is it possible to run Wordpad by just typing its name even though it isn’t on the PATH?

July 25, 2011 Jul 25, 2011 07/25/11

Raymond Chen

It's in the App Paths.