February 2016 | The Old New Thing

The 2016/2017 Seattle Symphony subscription season at a glance

Raymond ChenFebruary 29, 2016Feb 29, 201602/29/16

For many years, I've put together a little pocket guide to the Seattle Symphony subscription season for my symphony friends to help them decide which ticket package they want. For the past several years now, we haven't ordered any tickets at all because we all have young children, but I still make this guide out of some sense of obligation. S

How can I get the original shortcut target path with environment variables unexpanded?

Raymond ChenFebruary 29, 2016Feb 29, 201602/29/16

A customer wanted to be able to get the target of a shortcut with environment variables unexpanded. The IShellLink::GetPath method will expand environment variables. The way to get the unexpanded target path is to go for the EXP_SZ_LINK data in the shell link data list. We briefly encountered the shell link data list a while back. Now we

Changing a loop into a promise or task chain

Raymond ChenFebruary 26, 2016Feb 26, 201602/26/16

If you are dealing with PPL Tasks in C++ or Promises in JavaScript, you run into the problem of having to rephrase loops in the form of callbacks. (On the other hand, if you're using Tasks in C#, then you have the wonderful await keyword to do this all for you. If you're a JavaScript programmer, you can look at the async keyword coming to ES7.

How do I preload a chunk of memory into a memory-mapped file?

Raymond ChenFebruary 25, 2016Feb 25, 201602/25/16

A customer had a moderate-sized memory-mapped file (a few dozen megabytes), and they wanted to preload the entire file into memory because their program accesses the contents of the file non-sequentially, which means the normal prefetcher cannot anticipate which page to preload. They are forcing the pages to be preloaded by manually walking th

A static_cast is not always just a pointer adjustment

Raymond ChenFebruary 24, 2016Feb 24, 201602/24/16

Even without considering virtual base classes, a static_cast to move between a base class and a derived class can be more than just a pointer adjustment. Consider the following classes and functions. Suppose the compiler decided to lay out the memory for C like this: Now, you would think that converting a pointer to a C into a pointer to a

Why does the date disappear from my taskbar, sometimes?

Raymond ChenFebruary 23, 2016Feb 23, 201602/23/16

A customer reported that the date vanished from their taskbar, but it was there yesterday. They included a screen shot, which showed a vertically-docked taskbar on a Chinese system, and the clock showed simply "10:50". The customer sent the message on October 10. I used my psychic powers to debug the problem. Maybe you can too. (Time passes.

Finding the shortest binary string in a given interval

Raymond ChenFebruary 22, 2016Feb 22, 201602/22/16

Today's Little Program answers the question, "Given an interval of real numbers, find the shortest binary string that fits in that interval." For example, if you are given the range 0.1…0.3, then the answer is 0.25, whose binary representation is 0.01. Another way of phrasing the problem is that you are to find the simplest dyadic ratio

When I try to calculate a performance counter manually, the answer is off by a factor of 100

Raymond ChenFebruary 19, 2016Feb 19, 201602/19/16

A customer was having difficulty calculating a performance counter manually. According to the formula in the documentation, performance counters that are of type PERF_PRECISION_100NS_TIMER should be calculated as (N₁−N₀)/(D₁−D₀). But when we do that, the results we get are a factor of 100 smaller than th

Nasty gotcha: VarCmp vs VariantCompare

Raymond ChenFebruary 18, 2016Feb 18, 201602/18/16

There are two functions for comparing VARIANTs. One comes from the COM team, called VarCmp. Assuming a successful comparison, it returns This is consistent with the other VarXxx functions. On the other hand, the VariantCompare function comes from the shell, and it returns Yuck. So be careful which one you're calling and how you

Don’t just grab the foreground window and host UI on it, redux

Raymond ChenFebruary 17, 2016Feb 17, 201602/17/16

Some time ago, I advised, "Don't just grab the foreground window and host UI on it." Today I learned of another application that failed to heed this advice. When the application's installer is launched,¹ it calls GetForegroundWindow and uses that window as the owner for its dialogs. In particular, if you install the app by typi

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