The Old New Thing

August 2012 - The Old New Thing

Adventures in undefined behavior: The premature downcast

August 31, 2012 Aug 31, 2012 08/31/12
Raymond Chen
A customer encountered the following problem: The function converts the cookie back to a object, and then checks if the object is a object by calling . If so, then it does some more stuff to figure out what type of paint to buy. (Note to nitpickers: The actual scenario was not like this, but I presented it this way to illustrate the ...

I'm not calling a virtual function from my constructor or destructor, but I'm still getting a __purecall error

August 30, 2012 Aug 30, 2012 08/30/12
Raymond Chen
Some time ago, I described what is for: It's to detect the cases where you call a virtual method with no implementation (a so-called pure virtual method). This can happen during object constructor or destruction, since those are times when you can validly have a partially-implemented object. Well, there's another case this can happen: If ...

Psychic debugging: Why Chinese characters don't work

August 29, 2012 Aug 29, 2012 08/29/12
Raymond Chen
Here's a walkthrough of an actual case of psychic debugging. I'm using the internal XYZ table-generating tool, but it appears to be useless in my case. Does this tool work? Right now, I'm just resorting to the manual method of generating my data table (Chinese and English). Hooray for vague questions! "It appears to be useless." But there ...

Well at least nobody's parking there any more

August 28, 2012 Aug 28, 2012 08/28/12
Raymond Chen
There is a field next to the Microsoft building I used to work in, and for a time, people parked their cars out on the field, presumably because finding a proper parking space in the garage became difficult due to overcrowding. To prevent people from parking in the field, Security placed a large log across the access to the field. The ...

Dumping a hash table with external chaining from the debugger

August 24, 2012 Aug 24, 2012 08/24/12
Raymond Chen
I was doing some crash dump debugging, as I am often called upon to do, and one of the data structure I had to grovel through was something that operated basically like an atom table, so that's what I'll call it. Like an atom table, it manages a collection of strings. You can add a string to the table (getting a unique value back, which we ...

Wait, you never said that I had to initialize the object before I used it!

August 23, 2012 Aug 23, 2012 08/23/12
Raymond Chen
A customer reported that they were having trouble creating slim reader/writer locks at runtime. They simplified the issue to a short program: "What is the correct way of creating an via the operator?" It wasn't long before somebody noted that nowhere in the code is the function called. "Oh, yeah, thanks for catching that. It looks ...

The shifting sands of "Run as different user"

August 22, 2012 Aug 22, 2012 08/22/12
Raymond Chen
A customer liaison asked the following question on behalf of his customer. When I do a shift-right-click on a shortcut to a program, I see the following: The option to run a program as another user (other than Administrator) was present in Windows XP, but it was lost in Windows Vista. It appears that we responded to those ...

Sorry we got cut off, my phone just auto-rebooted

August 21, 2012 Aug 21, 2012 08/21/12
Raymond Chen
Some time ago, I was on the phone when the connection suddenly cut out. I looked at the my phone display and it said, Auto-restart in 7 seconds. The seconds counted down, and then the phone rebooted, and after about ten more seconds, it was back in business, acting like nothing was wrong. (Except that it just terminated a phone call without ...