The Old New Thing

February 2013 - The Old New Thing

What does 1#J mean? A strange corner case of the printing of special values

February 28, 2013 Feb 28, 2013 02/28/13
Raymond Chen
As a puzzle, commenter nobugz asks, "What kind of infinity is 1.#J?" double z = 0; printf("%.2f", 1/z); Now, the division by zero results in IEEE positive infinity, would would normally be printed as 1#INF. But the catch here is that the print format says "Display at most two places after the decimal point." But where is the decimal point...

When the option becomes so second-nature you forget that it’s an option

February 27, 2013 Feb 27, 2013 02/27/13
Raymond Chen
A user of the imaginary Program Q program wanted to write an automated test that created a table, then ran various sub-test which communicated among each other by updating that table. When my test tries to create a table, the program asks the following question: q install server -r testdb Setting up this machine to be a registered...

This code would be a lot faster if it weren’t for the synchronization

February 26, 2013 Feb 26, 2013 02/26/13
Raymond Chen
This is a story from a friend of a friend, which makes it probably untrue, but I still like the story. One of my colleagues jokingly suggested that we could speed up our code by adding these lines to our project #define EnterCriticalSection(p) ((void)0) #define LeaveCriticalSection(p) ((void)0) I replied, "You think you're joking, but ...

Now that version 4 of the .NET Framework supports in-process side-by-side runtimes, is it now okay to write shell extensions in managed code?

February 22, 2013 Feb 22, 2013 02/22/13
Raymond Chen
Many years ago, I wrote, "Do not write in-process shell extensions in managed code." Since I originally wrote that article, version 4 of the .NET Framework was released, and one of the features of that version is that it supports in-process side-by-side runtimes. Does that mean that it's now okay to write shell extensions in managed code? ...

Isn’t the CompletionKey parameter to CreateIoCompletionPort superfluous?

February 22, 2013 Feb 22, 2013 02/22/13
Raymond Chen
When you associate a file handle with an I/O completion port with the function, you can pass an arbitrary pointer-sized integer called the which will be returned by the function for every I/O that completes against that file handle. But isn't that parameter superfluous? If somebody wanted to associated additional data with a file handle...

What does -1.#IND mean?: A survey of how the Visual C runtime library prints special floating point values

February 21, 2013 Feb 21, 2013 02/21/13
Raymond Chen
As every computer scientist knows, the IEEE floating point format reserves a number of representations for infinity and non-numeric values (collectively known as NaN, short for not a number). If you try to print one of these special values with the Visual C runtime library, you will get a corresponding special result: Positive and ...

You can ask the compiler to answer your calling convention questions

February 20, 2013 Feb 20, 2013 02/20/13
Raymond Chen
If you want to figure out some quirks of a calling convention, you can always ask the compiler to do it for you, on the not unreasonable assumption that the compiler understands calling conventions. "When a __stdcall function returns a large structure by value, there is a hidden first parameter that specifies the address the return value ...