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Opportunistic locks allow you to be notified when somebody else tries to access a file you have open. This is usually done if you want to use a file provided nobody else wants it. For example, you might be a search indexer that wants to extract information from a file, but if somebody opens the file for writing, you don't want them to get Sharin...

A customer liaison asked whether it was legal to use to create a parent/child relationship between windows which belong to different processes. "If I remember correctly, the documentation for used to contain a stern warning that it is not supported, but that remark does not appear to be present any more. I have a customer who is reparenting windo...

Today's Little Program is a managed version of the text-extraction program from several years ago. It turns out that it's pretty easy in managed code because the accessibility folks sat down and wrote a whole framework for you, known as UI Automation. (Some people are under the mistaken impression that UI Automation works only for extracting d...

A customer was having trouble with job objects, specifically, the customer found that a Wait­For­Single­Object on a job object was not completing even though all the processes in the job had exited. This is probably the most frustrating part of job objects: A job object does not become signaled when all processes have exited. The s...

The Read­File and Write­File functions have a parameter called lp­Number­Of­Byte­Read, which is documented as __out_opt LPDWORD lpNumberOfBytesRead, // or __out_opt LPDWORD lpNumberOfBytesWritten, "Cool," you think. "That parameter is optional, and I can safely pass NULL." My program runs fine if standard output ...

Suppose you have a TreeView control, and you created an item in it, and you want to move the to a new parent. How do you do that? You can't, at least not all in one motion. You will have to delete the and then re-create it in its new location. If you want to move an within the same parent (say, to reorder it among its siblings), then you...

The IMessage­Filter::Handle­Incoming­Call method describes the incoming call by means of an INTERFACE­INFO structure: typedef struct tagINTERFACEINFO { LPUNKNOWN pUnk; IID iid; WORD wMethod; } INTERFACEINFO, *LPINTERFACEINFO; The wMethod is a zero-based index of the method within the interface. For example, IUnknown...

Today's Little Program monitors windows as they come and go. When people contemplate doing this, they come up with ideas like installing a WH_CBT hook or a WH_SHELL hook, but one of the major problems with those types of hooks is that they are injected hooks. Injection is bad for a number of reasons. It forces the hook to be in a DLL so it can be...

A source of great consternation is the mysterious return value from : If there is an error, the return value is −1. For example, the function fails if is an invalid window handle or is an invalid pointer. That paragraph has caused all sorts of havoc, because it throws into disarray the standard message pump: But don't worry, the standard m...

A customer reported that when their program called to get the icon for a folder, the call failed. "It works on some machines but not others. We don't know what the difference is between the working and non-working machines." They included the offending function from their program, but everything in the function looked good. The problem was somethi...