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| <h3 class="section">17.6 Line Control Functions</h3> |
| |
| <p><a name="index-terminal-line-control-functions-2001"></a> |
| These functions perform miscellaneous control actions on terminal |
| devices. As regards terminal access, they are treated like doing |
| output: if any of these functions is used by a background process on its |
| controlling terminal, normally all processes in the process group are |
| sent a <code>SIGTTOU</code> signal. The exception is if the calling process |
| itself is ignoring or blocking <code>SIGTTOU</code> signals, in which case the |
| operation is performed and no signal is sent. See <a href="Job-Control.html#Job-Control">Job Control</a>. |
| |
| <p><a name="index-break-condition_002c-generating-2002"></a><!-- termios.h --> |
| <!-- POSIX.1 --> |
| |
| <div class="defun"> |
| — Function: int <b>tcsendbreak</b> (<var>int filedes, int duration</var>)<var><a name="index-tcsendbreak-2003"></a></var><br> |
| <blockquote><p>This function generates a break condition by transmitting a stream of |
| zero bits on the terminal associated with the file descriptor |
| <var>filedes</var>. The duration of the break is controlled by the |
| <var>duration</var> argument. If zero, the duration is between 0.25 and 0.5 |
| seconds. The meaning of a nonzero value depends on the operating system. |
| |
| <p>This function does nothing if the terminal is not an asynchronous serial |
| data port. |
| |
| <p>The return value is normally zero. In the event of an error, a value |
| of -1 is returned. The following <code>errno</code> error conditions |
| are defined for this function: |
| |
| <dl> |
| <dt><code>EBADF</code><dd>The <var>filedes</var> is not a valid file descriptor. |
| |
| <br><dt><code>ENOTTY</code><dd>The <var>filedes</var> is not associated with a terminal device. |
| </dl> |
| </p></blockquote></div> |
| |
| <p><a name="index-flushing-terminal-output-queue-2004"></a><a name="index-terminal-output-queue_002c-flushing-2005"></a><!-- termios.h --> |
| <!-- POSIX.1 --> |
| |
| <div class="defun"> |
| — Function: int <b>tcdrain</b> (<var>int filedes</var>)<var><a name="index-tcdrain-2006"></a></var><br> |
| <blockquote><p>The <code>tcdrain</code> function waits until all queued |
| output to the terminal <var>filedes</var> has been transmitted. |
| |
| <p>This function is a cancellation point in multi-threaded programs. This |
| is a problem if the thread allocates some resources (like memory, file |
| descriptors, semaphores or whatever) at the time <code>tcdrain</code> is |
| called. If the thread gets canceled these resources stay allocated |
| until the program ends. To avoid this calls to <code>tcdrain</code> should be |
| protected using cancellation handlers. |
| <!-- ref pthread_cleanup_push / pthread_cleanup_pop --> |
| |
| <p>The return value is normally zero. In the event of an error, a value |
| of -1 is returned. The following <code>errno</code> error conditions |
| are defined for this function: |
| |
| <dl> |
| <dt><code>EBADF</code><dd>The <var>filedes</var> is not a valid file descriptor. |
| |
| <br><dt><code>ENOTTY</code><dd>The <var>filedes</var> is not associated with a terminal device. |
| |
| <br><dt><code>EINTR</code><dd>The operation was interrupted by delivery of a signal. |
| See <a href="Interrupted-Primitives.html#Interrupted-Primitives">Interrupted Primitives</a>. |
| </dl> |
| </p></blockquote></div> |
| |
| <p><a name="index-clearing-terminal-input-queue-2007"></a><a name="index-terminal-input-queue_002c-clearing-2008"></a><!-- termios.h --> |
| <!-- POSIX.1 --> |
| |
| <div class="defun"> |
| — Function: int <b>tcflush</b> (<var>int filedes, int queue</var>)<var><a name="index-tcflush-2009"></a></var><br> |
| <blockquote><p>The <code>tcflush</code> function is used to clear the input and/or output |
| queues associated with the terminal file <var>filedes</var>. The <var>queue</var> |
| argument specifies which queue(s) to clear, and can be one of the |
| following values: |
| |
| <!-- Extra blank lines here make it look better. --> |
| |
| <a name="index-TCIFLUSH-2010"></a> |
| <dl><dt><code>TCIFLUSH</code><dd> |
| Clear any input data received, but not yet read. |
| |
| <p><a name="index-TCOFLUSH-2011"></a><br><dt><code>TCOFLUSH</code><dd> |
| Clear any output data written, but not yet transmitted. |
| |
| <p><a name="index-TCIOFLUSH-2012"></a><br><dt><code>TCIOFLUSH</code><dd> |
| Clear both queued input and output. |
| </dl> |
| |
| <p>The return value is normally zero. In the event of an error, a value |
| of -1 is returned. The following <code>errno</code> error conditions |
| are defined for this function: |
| |
| <dl> |
| <dt><code>EBADF</code><dd>The <var>filedes</var> is not a valid file descriptor. |
| |
| <br><dt><code>ENOTTY</code><dd>The <var>filedes</var> is not associated with a terminal device. |
| |
| <br><dt><code>EINVAL</code><dd>A bad value was supplied as the <var>queue</var> argument. |
| </dl> |
| |
| <p>It is unfortunate that this function is named <code>tcflush</code>, because |
| the term “flush” is normally used for quite another operation—waiting |
| until all output is transmitted—and using it for discarding input or |
| output would be confusing. Unfortunately, the name <code>tcflush</code> comes |
| from POSIX and we cannot change it. |
| </p></blockquote></div> |
| |
| <p><a name="index-flow-control_002c-terminal-2013"></a><a name="index-terminal-flow-control-2014"></a><!-- termios.h --> |
| <!-- POSIX.1 --> |
| |
| <div class="defun"> |
| — Function: int <b>tcflow</b> (<var>int filedes, int action</var>)<var><a name="index-tcflow-2015"></a></var><br> |
| <blockquote><p>The <code>tcflow</code> function is used to perform operations relating to |
| XON/XOFF flow control on the terminal file specified by <var>filedes</var>. |
| |
| <p>The <var>action</var> argument specifies what operation to perform, and can |
| be one of the following values: |
| |
| |
| <a name="index-TCOOFF-2016"></a> |
| <dl><dt><code>TCOOFF</code><dd>Suspend transmission of output. |
| |
| <p><a name="index-TCOON-2017"></a><br><dt><code>TCOON</code><dd>Restart transmission of output. |
| |
| <p><a name="index-TCIOFF-2018"></a><br><dt><code>TCIOFF</code><dd>Transmit a STOP character. |
| |
| <p><a name="index-TCION-2019"></a><br><dt><code>TCION</code><dd>Transmit a START character. |
| </dl> |
| |
| <p>For more information about the STOP and START characters, see <a href="Special-Characters.html#Special-Characters">Special Characters</a>. |
| |
| <p>The return value is normally zero. In the event of an error, a value |
| of -1 is returned. The following <code>errno</code> error conditions |
| are defined for this function: |
| |
| |
| <a name="index-EBADF-2020"></a> |
| <dl><dt><code>EBADF</code><dd>The <var>filedes</var> is not a valid file descriptor. |
| |
| <p><a name="index-ENOTTY-2021"></a><br><dt><code>ENOTTY</code><dd>The <var>filedes</var> is not associated with a terminal device. |
| |
| <p><a name="index-EINVAL-2022"></a><br><dt><code>EINVAL</code><dd>A bad value was supplied as the <var>action</var> argument. |
| </dl> |
| </p></blockquote></div> |
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