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

Raymond Chen February 29, 2016 Feb 29, 2016 02/29/16

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 Chen February 26, 2016 Feb 26, 2016 02/26/16

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 Chen February 25, 2016 Feb 25, 2016 02/25/16

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 ...

A static_cast is not always just a pointer adjustment

Raymond Chen February 24, 2016 Feb 24, 2016 02/24/16

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...

Finding the shortest binary string in a given interval

Raymond Chen February 22, 2016 Feb 22, 2016 02/22/16

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 ...

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

Raymond Chen February 19, 2016 Feb 19, 2016 02/19/16

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 ...

Nasty gotcha: VarCmp vs VariantCompare

Raymond Chen February 18, 2016 Feb 18, 2016 02/18/16

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 Chen February 17, 2016 Feb 17, 2016 02/17/16

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 ...