Last time, we learned about the dangers of uninitialized floating point variables but left with a puzzle: Why wasn't this caught during internal testing? I dropped a hint when I described how SNaNs work: You have to ask the processor to raise an exception when it encounters a signaling NaN, and the program disabled that exception. Why was an ...

A colleague of mine related to me this story about uninitialized floating point variables. He had a function that went something like this, simplified for expository purposes. The infoType parameter specified which piece of information you're requesting, and depending on what you're asking for, one or the other of the output parameters may not ...

A customer needed to generate an 8-byte unique value, and their initial idea was to generate a GUID and throw away the second half, keeping the first eight bytes. They wanted to know if this was a good idea. No, it's not a good idea. The GUID generation algorithm relies on the fact that it has all 16 bytes to use to ...

It's great when you have a tool to make programming easier, but you still must understand what it does or you're just replacing one set of problems with another set of more subtle problems. For example, we discussed earlier the importance of knowing when your destructor runs. Here's another example, courtesy of my colleague Chris Ashton. This ...

Commenter Chris Becke asks how the common controls convert ANSI parameters to Unicode, since the common controls are Unicode internally. Everything goes through CP_ACP, pretty much by definition. The ANSI code page is CP_ACP. That's what ACP stands for, after all. Now, there are some function families that do not use ANSI. The console ...

There are many situations where you pass a structure to a function, and the function fills in the structure with information you request. In some cases, the function always fills in the entire structure (example: GlobalMemoryStatus). In other cases, you tell the function which bits of information you care about, to save the function the effort of ...

This is really just a corollary to Why are DLLs unloaded in the ''wrong'' order. Exactly the same logic that explains why DLLs are unloaded in the ''wrong'' order also explains why they are uninitialized in the ''wrong'' order. Once you understand the first issue, the second comes for free; just change DLL_PROCESS_DETACH to DLL_THREAD_DETACH in ...

A customer noticed that if you add three to a process ID and pass it to the OpenProcess function, it still succeeds. Why is that? Well, first of all, I need to say up front that the behavior you're seeing is an artifact of the implementation and is not part of the contract. You're passing intentionally invalid parameters, what did you ...

In the suggestion box, Serge Wautier asked why accelerators for hidden controls remain active. He's apparently rather insistent because he asked the question again a few months later. Asking the same question multiple times reduces the likelihood that I'll answer it. Consider yourself lucky that I wrote this answer before I noticed the ...

Shell extensions that create worker threads need to call the SHGetInstanceExplorer function so that Explorer will not exit while the worker thread is still running. When your worker thread finishes, you release the IUnknown that you obtained to tell the host program, ''Okay, I'm done now, thanks for waiting.'' You can read this contract from ...