The Old New Thing

Code - The Old New Thing

Understanding what things mean in context: Dispatch interfaces

January 16, 2006 Jan 16, 2006 01/16/06
Raymond Chen
Remember that you have to understand what things mean in context. For example, the IActiveMovie3 interface has a method called get_MediaPlayer. If you come into this method without any context, you might expect it to return a pointer to an IMediaPlayer interface, yet the header file says that it returns a pointer to an IDispatch interface ...

Converting between LCIDs and RFC 1766 language codes

January 5, 2006 Jan 5, 2006 01/5/06
Raymond Chen
Occasionally, I see someone ask for a function that converts between LCIDs (such as 0x0409 for English-US) and RFC 1766 language identifiers (such as "en-us"). The rule of thumb is, if it's something a web browser would need, and it has to do with locales and languages, you should look in the MLang library. In this case, the ...

Taxes: Detecting session state changes, such as a locked workstation

January 4, 2006 Jan 4, 2006 01/4/06
Raymond Chen
Another developer tax is playing friendly with Fast User Switching and Terminal Services. When the workstation is locked or disconnected, you should turn off non-essential timers, minimize background activities, and generally send your program into a quiet state. If you already used the technique of painting only when your window is visible ...

Taxes: Remote Desktop Connection and painting

January 3, 2006 Jan 3, 2006 01/3/06
Raymond Chen
An increasingly important developer tax is supporting Remote Desktop Connection properly. When the user is connected via a Remote Desktop Connection, video operations are transferred over the network connection to the client for display. Since networks have high latency and nowhere near the bandwidth of a local PCI or AGP bus, you need to ...

The world's slowest RET instruction

January 3, 2006 Jan 3, 2006 01/3/06
Raymond Chen
Occasionally, somebody will ask I'm debugging a hang, and I see that many threads are stuck at a RET instruction. When I try to trace one instruction from that thread, the trace breakpoint never fires. It's as if the RET instruction itself is wedged! I've found the world's slowest RET instruction. (A common variation on this theme is that ...

On the abuse of properties

January 3, 2006 Jan 3, 2006 01/3/06
Raymond Chen
One thing that I see occasionally is the abuse of property syntax. IDispatch and CLR objects (and C++ objects if you want to avail yourself of a Microsoft-specific extension) support "properties", which syntactically look like fields but internally are treated as a pair of methods ("get" and "put"). An important principle is that given an ...

There's more to calling a function than just getting the types to match

January 3, 2006 Jan 3, 2006 01/3/06
Raymond Chen
Here's a classic novice error. You want to call a function, say GetBinaryType. What should you write for those question marks? Well, the prototype says that the second parameter is an LPDWORD, so let's pass it one. Hm, but that crashes. Well, maybe we can pass it an LPDWORD this way: Hm, that still crashes. Oh wait, it's because ...

On the ambiguity of uniqueness

December 14, 2005 Dec 14, 2005 12/14/05
Raymond Chen
The MSDN documentation for says [T]he implementation of GetHashCode provided by the String class returns unique hash codes for unique string values. This is another case of ambiguous use of the word "unique". The intended meaning is "for each string value, the same hash code is returned". Even though "unique" means "one and only one...

Your debugging code can be a security hole

December 12, 2005 Dec 12, 2005 12/12/05
Raymond Chen
When you're developing your debugging code, don't forget that just because it's only for debugging doesn't mean that you can forget about security. I remember one customer who asked (paraphrased) We have a service, and for testing purposes we want to be able to connect to this service and extract the private data that the service is ...