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| <h4 class="subsection">17.4.4 Input Modes</h4> |
| |
| <p>This section describes the terminal attribute flags that control |
| fairly low-level aspects of input processing: handling of parity errors, |
| break signals, flow control, and <RET> and <LFD> characters. |
| |
| <p>All of these flags are bits in the <code>c_iflag</code> member of the |
| <code>struct termios</code> structure. The member is an integer, and you |
| change flags using the operators <code>&</code>, <code>|</code> and <code>^</code>. Don't |
| try to specify the entire value for <code>c_iflag</code>—instead, change |
| only specific flags and leave the rest untouched (see <a href="Setting-Modes.html#Setting-Modes">Setting Modes</a>). |
| |
| <!-- termios.h --> |
| <!-- POSIX.1 --> |
| <div class="defun"> |
| — Macro: tcflag_t <b>INPCK</b><var><a name="index-INPCK-1869"></a></var><br> |
| <blockquote><p><a name="index-parity-checking-1870"></a>If this bit is set, input parity checking is enabled. If it is not set, |
| no checking at all is done for parity errors on input; the |
| characters are simply passed through to the application. |
| |
| <p>Parity checking on input processing is independent of whether parity |
| detection and generation on the underlying terminal hardware is enabled; |
| see <a href="Control-Modes.html#Control-Modes">Control Modes</a>. For example, you could clear the <code>INPCK</code> |
| input mode flag and set the <code>PARENB</code> control mode flag to ignore |
| parity errors on input, but still generate parity on output. |
| |
| <p>If this bit is set, what happens when a parity error is detected depends |
| on whether the <code>IGNPAR</code> or <code>PARMRK</code> bits are set. If neither |
| of these bits are set, a byte with a parity error is passed to the |
| application as a <code>'\0'</code> character. |
| </p></blockquote></div> |
| |
| <!-- termios.h --> |
| <!-- POSIX.1 --> |
| <div class="defun"> |
| — Macro: tcflag_t <b>IGNPAR</b><var><a name="index-IGNPAR-1871"></a></var><br> |
| <blockquote><p>If this bit is set, any byte with a framing or parity error is ignored. |
| This is only useful if <code>INPCK</code> is also set. |
| </p></blockquote></div> |
| |
| <!-- termios.h --> |
| <!-- POSIX.1 --> |
| <div class="defun"> |
| — Macro: tcflag_t <b>PARMRK</b><var><a name="index-PARMRK-1872"></a></var><br> |
| <blockquote><p>If this bit is set, input bytes with parity or framing errors are marked |
| when passed to the program. This bit is meaningful only when |
| <code>INPCK</code> is set and <code>IGNPAR</code> is not set. |
| |
| <p>The way erroneous bytes are marked is with two preceding bytes, |
| <code>377</code> and <code>0</code>. Thus, the program actually reads three bytes |
| for one erroneous byte received from the terminal. |
| |
| <p>If a valid byte has the value <code>0377</code>, and <code>ISTRIP</code> (see below) |
| is not set, the program might confuse it with the prefix that marks a |
| parity error. So a valid byte <code>0377</code> is passed to the program as |
| two bytes, <code>0377</code> <code>0377</code>, in this case. |
| </p></blockquote></div> |
| |
| <!-- termios.h --> |
| <!-- POSIX.1 --> |
| <div class="defun"> |
| — Macro: tcflag_t <b>ISTRIP</b><var><a name="index-ISTRIP-1873"></a></var><br> |
| <blockquote><p>If this bit is set, valid input bytes are stripped to seven bits; |
| otherwise, all eight bits are available for programs to read. |
| </p></blockquote></div> |
| |
| <!-- termios.h --> |
| <!-- POSIX.1 --> |
| <div class="defun"> |
| — Macro: tcflag_t <b>IGNBRK</b><var><a name="index-IGNBRK-1874"></a></var><br> |
| <blockquote><p>If this bit is set, break conditions are ignored. |
| |
| <p><a name="index-break-condition_002c-detecting-1875"></a>A <dfn>break condition</dfn> is defined in the context of asynchronous |
| serial data transmission as a series of zero-value bits longer than a |
| single byte. |
| </p></blockquote></div> |
| |
| <!-- termios.h --> |
| <!-- POSIX.1 --> |
| <div class="defun"> |
| — Macro: tcflag_t <b>BRKINT</b><var><a name="index-BRKINT-1876"></a></var><br> |
| <blockquote><p>If this bit is set and <code>IGNBRK</code> is not set, a break condition |
| clears the terminal input and output queues and raises a <code>SIGINT</code> |
| signal for the foreground process group associated with the terminal. |
| |
| <p>If neither <code>BRKINT</code> nor <code>IGNBRK</code> are set, a break condition is |
| passed to the application as a single <code>'\0'</code> character if |
| <code>PARMRK</code> is not set, or otherwise as a three-character sequence |
| <code>'\377'</code>, <code>'\0'</code>, <code>'\0'</code>. |
| </p></blockquote></div> |
| |
| <!-- termios.h --> |
| <!-- POSIX.1 --> |
| <div class="defun"> |
| — Macro: tcflag_t <b>IGNCR</b><var><a name="index-IGNCR-1877"></a></var><br> |
| <blockquote><p>If this bit is set, carriage return characters (<code>'\r'</code>) are |
| discarded on input. Discarding carriage return may be useful on |
| terminals that send both carriage return and linefeed when you type the |
| <RET> key. |
| </p></blockquote></div> |
| |
| <!-- termios.h --> |
| <!-- POSIX.1 --> |
| <div class="defun"> |
| — Macro: tcflag_t <b>ICRNL</b><var><a name="index-ICRNL-1878"></a></var><br> |
| <blockquote><p>If this bit is set and <code>IGNCR</code> is not set, carriage return characters |
| (<code>'\r'</code>) received as input are passed to the application as newline |
| characters (<code>'\n'</code>). |
| </p></blockquote></div> |
| |
| <!-- termios.h --> |
| <!-- POSIX.1 --> |
| <div class="defun"> |
| — Macro: tcflag_t <b>INLCR</b><var><a name="index-INLCR-1879"></a></var><br> |
| <blockquote><p>If this bit is set, newline characters (<code>'\n'</code>) received as input |
| are passed to the application as carriage return characters (<code>'\r'</code>). |
| </p></blockquote></div> |
| |
| <!-- termios.h --> |
| <!-- POSIX.1 --> |
| <div class="defun"> |
| — Macro: tcflag_t <b>IXOFF</b><var><a name="index-IXOFF-1880"></a></var><br> |
| <blockquote><p>If this bit is set, start/stop control on input is enabled. In other |
| words, the computer sends STOP and START characters as necessary to |
| prevent input from coming in faster than programs are reading it. The |
| idea is that the actual terminal hardware that is generating the input |
| data responds to a STOP character by suspending transmission, and to a |
| START character by resuming transmission. See <a href="Start_002fStop-Characters.html#Start_002fStop-Characters">Start/Stop Characters</a>. |
| </p></blockquote></div> |
| |
| <!-- termios.h --> |
| <!-- POSIX.1 --> |
| <div class="defun"> |
| — Macro: tcflag_t <b>IXON</b><var><a name="index-IXON-1881"></a></var><br> |
| <blockquote><p>If this bit is set, start/stop control on output is enabled. In other |
| words, if the computer receives a STOP character, it suspends output |
| until a START character is received. In this case, the STOP and START |
| characters are never passed to the application program. If this bit is |
| not set, then START and STOP can be read as ordinary characters. |
| See <a href="Start_002fStop-Characters.html#Start_002fStop-Characters">Start/Stop Characters</a>. |
| <!-- !!! mention this interferes with using C-s and C-q for programs like emacs --> |
| </p></blockquote></div> |
| |
| <!-- termios.h --> |
| <!-- BSD --> |
| <div class="defun"> |
| — Macro: tcflag_t <b>IXANY</b><var><a name="index-IXANY-1882"></a></var><br> |
| <blockquote><p>If this bit is set, any input character restarts output when output has |
| been suspended with the STOP character. Otherwise, only the START |
| character restarts output. |
| |
| <p>This is a BSD extension; it exists only on BSD systems and the GNU system. |
| </p></blockquote></div> |
| |
| <!-- termios.h --> |
| <!-- BSD --> |
| <div class="defun"> |
| — Macro: tcflag_t <b>IMAXBEL</b><var><a name="index-IMAXBEL-1883"></a></var><br> |
| <blockquote><p>If this bit is set, then filling up the terminal input buffer sends a |
| BEL character (code <code>007</code>) to the terminal to ring the bell. |
| |
| <p>This is a BSD extension. |
| </p></blockquote></div> |
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