In the ReadDirectoryChangesW Function what does the Overlap parameter mean?

Question

I understand the the ReadDirectoryChangesW Function uses a buffer to store the notifications, but what does overlap mean?

I presume there is protection to stop the notification you're reading from being over-written?

Answer 1

It is for asynchronous operations.

A call to ReadDirectoryChangesW can be completed synchronously or asynchronously. To specify asynchronous completion, open the directory with CreateFile as shown above, but additionally specify the FILE_FLAG_OVERLAPPED attribute in the dwFlagsAndAttributes parameter. Then specify an OVERLAPPED structure when you call ReadDirectoryChangesW.

See ReadDirectoryChangesW Function remarks sections.

Answer 2

this argument is for asynchronous operation.

on Windows, this is called "overlapped i/o". you can find this kind of parameter, with the same way of working, on a lot of function calls related to input/output (ReadFile, WriteFile, ...). more information about overlapped i/o can be found in the MSDN.