https://bugzilla.kernel.org/show_bug.cgi?id=91931 Bug ID: 91931 Summary: fflush(3) is misleading about input streams Product: Documentation Version: unspecified Hardware: All OS: Linux Status: NEW Severity: normal Priority: P1 Component: man-pages Assignee: documentation_man-pages@xxxxxxxxxxxxxxxxxxxx Reporter: cubbi@xxxxxxxxx Regression: No Current fflush(3) claims that "For input streams, fflush() discards any buffered data that has been fetched from the underlying file, but has not been consumed by the application." While technically true (assuming 'file' implies seekable device), this is incomplete: flushing an input stream associated with a non-seekable device, such as the terminal input, does nothing (the update to fp->_IO_read_end at libio/fileops.c:872 does not happen due to ESPIPE from lseek) There have been enough confused beginner posts to various internet forums asking why flushing stdin doesn't work on Linux. I believe it is worth making the man page more explicit. At the very least, it should begin that sentence with "For input streams associated with seekable devices", or perhaps it should mention the unfortunately popular use case fflush(stdin) explicitly. On a very minor note, fflush(3) also claims that "The standards do not specify the behavior for input streams" This is no longer precisely correct; POSIX specifies behavior for seekable input streams to move fileno's offset to match FILE's offset and undo all ungetc's: http://pubs.opengroup.org/onlinepubs/9699919799/functions/fflush.html and glibc conforms to that (or tries to, https://sourceware.org/bugzilla/show_bug.cgi?id=5994 is still open) -- You are receiving this mail because: You are watching the assignee of the bug. -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
