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FIONREAD(2const) — Linux manual page

FIONREAD(2const)FIONREAD(2const)

NAME        top

       FIONREAD, TIOCINQ, TIOCOUTQ, TCFLSH, TIOCSERGETLSR - buffer count       and flushing

LIBRARY        top

       Standard C library (libc,-lc)

SYNOPSIS        top

#include <asm/termbits.h>/* Definition of constants */#include <sys/ioctl.h>int ioctl(intfd, FIONREAD, int *argp);int ioctl(intfd, TIOCINQ, int *argp);int ioctl(intfd, TIOCOUTQ, int *argp);int ioctl(intfd, TCFLSH, intarg);int ioctl(intfd, TIOCSERGETLSR, int *argp);

DESCRIPTION        top

FIONREAD              Get the number of bytes in the input buffer.TIOCINQ              Same asFIONREAD.TIOCOUTQ              Get the number of bytes in the output buffer.TCFLSHEquivalent totcflush(fd, arg).              Seetcflush(3) for the argument valuesTCIFLUSH,TCOFLUSH,TCIOFLUSH.TIOCSERGETLSR              Get line status register.  Status register hasTIOCSER_TEMT              bit set when output buffer is empty and also hardware              transmitter is physically empty.              Does not have to be supported by all serial tty drivers.tcdrain(3) does not wait and returns immediately whenTIOCSER_TEMTbit is set.

RETURN VALUE        top

       On success, 0 is returned.  On error, -1 is returned, anderrno is       set to indicate the error.

SEE ALSO        top

ioctl(2),ioctl_tty(2),tcflush(3),termios(3)

COLOPHON        top

       This page is part of theman-pages (Linux kernel and C library       user-space interface documentation) project.  Information about       the project can be found at        ⟨https://www.kernel.org/doc/man-pages/⟩.  If you have a bug report       for this manual page, see       ⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.       This page was obtained from the tarball man-pages-6.15.tar.gz       fetched from       ⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on       2025-08-11.  If you discover any rendering problems in this HTML       version of the page, or you believe there is a better or more up-       to-date source for the page, or you have corrections or       improvements to the information in this COLOPHON (which isnot       part of the original manual page), send a mail to       man-pages@man7.orgLinux man-pages 6.15            2025-05-17FIONREAD(2const)

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