Hi, the current state of fflush() according to stdio.h is: Flush \c stream.
This is a null operation provided for source-code compatibility only, as the standard IO implementation currently does not perform any buffering. This is ok for the stream implementation itself if it is not buffering, but if the device driver which forms the base of the stream performs buffering it may be would like to be informed if fflush() is called to flush its own buffers. I currently run into this case because I have an interrupt-driven UART component which manages its own buffers. And especially during debugging fflush() is very helpful as messages may get stuck in the buffer before a crash and you are searching for the problem at the wrong location. A possible solution would be using a dedicated flush-function provided by the driver but this is neither elegant nor very portable. So a possible solution would be to extend the __file struct with a field containing a pointer to a driver provided flush-function and registering this function via a dedicated function. This has the two cons, that the structure would require more space (2 bytes) and that another auxiliary function is required. Another solution would be to change the prototype of the supplied put-function from int (*put)(char, FILE *) to int (*put)(int, FILE *) and use a magic value outside the range of char to trigger the flush-function. This has the big con, that the prototype has to be changed, and existent conforming code may cause a warning but (if I remember the ABI correctly) would still continue to work. There are a lot of other possible solutions and possible modifications of the above two (like using a dedicated flag to indicate the presence of the auxiliary field). Feel free to add other good solutions. If we agree on a method I could write the necessary patch. Best regards, Daniel
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