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| <h4 class="subsection">17.4.2 Terminal Mode Functions</h4> |
| |
| <p><a name="index-terminal-mode-functions-1862"></a> |
| <!-- termios.h --> |
| <!-- POSIX.1 --> |
| |
| <div class="defun"> |
| — Function: int <b>tcgetattr</b> (<var>int filedes, struct termios *termios-p</var>)<var><a name="index-tcgetattr-1863"></a></var><br> |
| <blockquote><p>This function is used to examine the attributes of the terminal |
| device with file descriptor <var>filedes</var>. The attributes are returned |
| in the structure that <var>termios-p</var> points to. |
| |
| <p>If successful, <code>tcgetattr</code> returns 0. A return value of -1 |
| indicates an error. The following <code>errno</code> error conditions are |
| defined for this function: |
| |
| <dl> |
| <dt><code>EBADF</code><dd>The <var>filedes</var> argument is not a valid file descriptor. |
| |
| <br><dt><code>ENOTTY</code><dd>The <var>filedes</var> is not associated with a terminal. |
| </dl> |
| </p></blockquote></div> |
| |
| <!-- termios.h --> |
| <!-- POSIX.1 --> |
| <div class="defun"> |
| — Function: int <b>tcsetattr</b> (<var>int filedes, int when, const struct termios *termios-p</var>)<var><a name="index-tcsetattr-1864"></a></var><br> |
| <blockquote><p>This function sets the attributes of the terminal device with file |
| descriptor <var>filedes</var>. The new attributes are taken from the |
| structure that <var>termios-p</var> points to. |
| |
| <p>The <var>when</var> argument specifies how to deal with input and output |
| already queued. It can be one of the following values: |
| |
| <dl> |
| <!-- termios.h --> |
| <!-- POSIX.1 --> |
| <dt><code>TCSANOW</code><dd><a name="index-TCSANOW-1865"></a>Make the change immediately. |
| |
| <!-- termios.h --> |
| <!-- POSIX.1 --> |
| <br><dt><code>TCSADRAIN</code><dd><a name="index-TCSADRAIN-1866"></a>Make the change after waiting until all queued output has been written. |
| You should usually use this option when changing parameters that affect |
| output. |
| |
| <!-- termios.h --> |
| <!-- POSIX.1 --> |
| <br><dt><code>TCSAFLUSH</code><dd><a name="index-TCSAFLUSH-1867"></a>This is like <code>TCSADRAIN</code>, but also discards any queued input. |
| |
| <!-- termios.h --> |
| <!-- BSD --> |
| <br><dt><code>TCSASOFT</code><dd><a name="index-TCSASOFT-1868"></a>This is a flag bit that you can add to any of the above alternatives. |
| Its meaning is to inhibit alteration of the state of the terminal |
| hardware. It is a BSD extension; it is only supported on BSD systems |
| and the GNU system. |
| |
| <p>Using <code>TCSASOFT</code> is exactly the same as setting the <code>CIGNORE</code> |
| bit in the <code>c_cflag</code> member of the structure <var>termios-p</var> points |
| to. See <a href="Control-Modes.html#Control-Modes">Control Modes</a>, for a description of <code>CIGNORE</code>. |
| </dl> |
| |
| <p>If this function is called from a background process on its controlling |
| terminal, normally all processes in the process group are sent a |
| <code>SIGTTOU</code> signal, in the same way as if the process were trying to |
| write to the terminal. 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>If successful, <code>tcsetattr</code> returns 0. A return value of |
| -1 indicates an error. The following <code>errno</code> error |
| conditions are defined for this function: |
| |
| <dl> |
| <dt><code>EBADF</code><dd>The <var>filedes</var> argument is not a valid file descriptor. |
| |
| <br><dt><code>ENOTTY</code><dd>The <var>filedes</var> is not associated with a terminal. |
| |
| <br><dt><code>EINVAL</code><dd>Either the value of the <code>when</code> argument is not valid, or there is |
| something wrong with the data in the <var>termios-p</var> argument. |
| </dl> |
| </p></blockquote></div> |
| |
| <p>Although <code>tcgetattr</code> and <code>tcsetattr</code> specify the terminal |
| device with a file descriptor, the attributes are those of the terminal |
| device itself and not of the file descriptor. This means that the |
| effects of changing terminal attributes are persistent; if another |
| process opens the terminal file later on, it will see the changed |
| attributes even though it doesn't have anything to do with the open file |
| descriptor you originally specified in changing the attributes. |
| |
| <p>Similarly, if a single process has multiple or duplicated file |
| descriptors for the same terminal device, changing the terminal |
| attributes affects input and output to all of these file |
| descriptors. This means, for example, that you can't open one file |
| descriptor or stream to read from a terminal in the normal |
| line-buffered, echoed mode; and simultaneously have another file |
| descriptor for the same terminal that you use to read from it in |
| single-character, non-echoed mode. Instead, you have to explicitly |
| switch the terminal back and forth between the two modes. |
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