terminal.texi

一个C源代码分析器

When a member contains a collection of independent flags, as the
@code{c_iflag}, @code{c_oflag} and @code{c_cflag} members do, even
setting the entire member is a bad idea, because particular operating
systems have their own flags.  Instead, you should start with the
current value of the member and alter only the flags whose values matter
in your program, leaving any other flags unchanged.

Here is an example of how to set one flag (@code{ISTRIP}) in the
@code{struct termios} structure while properly preserving all the other
data in the structure:

@smallexample
@group
int
set_istrip (int desc, int value)
@{
  struct termios settings;
  int result;
@end group

@group
  result = tcgetattr (desc, &settings);
  if (result < 0)
    @{
      perror ("error in tcgetattr");
      return 0;
    @}
@end group
@group
  settings.c_iflag &= ~ISTRIP;
  if (value)
    settings.c_iflag |= ISTRIP;
@end group
@group
  result = tcsetattr (desc, TCSANOW, &settings);
  if (result < 0)
    @{
      perror ("error in tcgetattr");
      return;
   @}
  return 1;
@}
@end group
@end smallexample

@node Input Modes
@subsection Input Modes

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 @key{RET} and @key{LFD} characters.

All of these flags are bits in the @code{c_iflag} member of the
@code{struct termios} structure.  The member is an integer, and you
change flags using the operators @code{&}, @code{|} and @code{^}.  Don't
try to specify the entire value for @code{c_iflag}---instead, change
only specific flags and leave the rest untouched (@pxref{Setting
Modes}).

@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t INPCK
@cindex parity checking
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.

Parity checking on input processing is independent of whether parity
detection and generation on the underlying terminal hardware is enabled;
see @ref{Control Modes}.  For example, you could clear the @code{INPCK}
input mode flag and set the @code{PARENB} control mode flag to ignore
parity errors on input, but still generate parity on output.

If this bit is set, what happens when a parity error is detected depends
on whether the @code{IGNPAR} or @code{PARMRK} 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'} character.
@end deftypevr

@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t IGNPAR
If this bit is set, any byte with a framing or parity error is ignored.
This is only useful if @code{INPCK} is also set.
@end deftypevr

@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t PARMRK
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} is set and @code{IGNPAR} is not set.

The way erroneous bytes are marked is with two preceding bytes,
@code{377} and @code{0}.  Thus, the program actually reads three bytes
for one erroneous byte received from the terminal.

If a valid byte has the value @code{0377}, and @code{ISTRIP} (see below)
is not set, the program might confuse it with the prefix that marks a
parity error.  So a valid byte @code{0377} is passed to the program as
two bytes, @code{0377} @code{0377}, in this case.
@end deftypevr

@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t ISTRIP
If this bit is set, valid input bytes are stripped to seven bits;
otherwise, all eight bits are available for programs to read.
@end deftypevr

@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t IGNBRK
If this bit is set, break conditions are ignored.

@cindex break condition, detecting
A @dfn{break condition} is defined in the context of asynchronous
serial data transmission as a series of zero-value bits longer than a
single byte.
@end deftypevr

@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t BRKINT
If this bit is set and @code{IGNBRK} is not set, a break condition
clears the terminal input and output queues and raises a @code{SIGINT}
signal for the foreground process group associated with the terminal.

If neither @code{BRKINT} nor @code{IGNBRK} are set, a break condition is
passed to the application as a single @code{'\0'} character if
@code{PARMRK} is not set, or otherwise as a three-character sequence 
@code{'\377'}, @code{'\0'}, @code{'\0'}.
@end deftypevr

@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t IGNCR
If this bit is set, carriage return characters (@code{'\r'}) are
discarded on input.  Discarding carriage return may be useful on
terminals that send both carriage return and linefeed when you type the
@key{RET} key.
@end deftypevr

@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t ICRNL
If this bit is set and @code{IGNCR} is not set, carriage return characters
(@code{'\r'}) received as input are passed to the application as newline
characters (@code{'\n'}).
@end deftypevr

@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t INLCR
If this bit is set, newline characters (@code{'\n'}) received as input
are passed to the application as carriage return characters (@code{'\r'}).
@end deftypevr

@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t IXOFF
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.  @xref{Start/Stop Characters}.
@end deftypevr

@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t IXON
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.
@xref{Start/Stop Characters}.
@c !!! mention this interferes with using C-s and C-q for programs like emacs
@end deftypevr

@comment termios.h
@comment BSD
@deftypevr Macro tcflag_t IXANY
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.

This is a BSD extension; it exists only on BSD systems and the GNU system.
@end deftypevr

@comment termios.h
@comment BSD
@deftypevr Macro tcflag_t IMAXBEL
If this bit is set, then filling up the terminal input buffer sends a
BEL character (code @code{007}) to the terminal to ring the bell.

This is a BSD extension.
@end deftypevr

@node Output Modes
@subsection Output Modes

This section describes the terminal flags and fields that control how
output characters are translated and padded for display.  All of these
are contained in the @code{c_oflag} member of the @w{@code{struct termios}}
structure.

The @code{c_oflag} member itself is an integer, and you change the flags
and fields using the operators @code{&}, @code{|}, and @code{^}.  Don't
try to specify the entire value for @code{c_oflag}---instead, change
only specific flags and leave the rest untouched (@pxref{Setting
Modes}).

@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t OPOST
If this bit is set, output data is processed in some unspecified way so
that it is displayed appropriately on the terminal device.  This
typically includes mapping newline characters (@code{'\n'}) onto
carriage return and linefeed pairs.

If this bit isn't set, the characters are transmitted as-is.
@end deftypevr

The following three bits are BSD features, and they exist only BSD
systems and the GNU system.  They are effective only if @code{OPOST} is
set.

@comment termios.h
@comment BSD
@deftypevr Macro tcflag_t ONLCR
If this bit is set, convert the newline character on output into a pair
of characters, carriage return followed by linefeed.
@end deftypevr

@comment termios.h
@comment BSD
@deftypevr Macro tcflag_t OXTABS
If this bit is set, convert tab characters on output into the appropriate
number of spaces to emulate a tab stop every eight columns.
@end deftypevr

@comment termios.h
@comment BSD
@deftypevr Macro tcflag_t ONOEOT
If this bit is set, discard @kbd{C-d} characters (code @code{004}) on
output.  These characters cause many dial-up terminals to disconnect.
@end deftypevr

@node Control Modes
@subsection Control Modes

This section describes the terminal flags and fields that control
parameters usually associated with asynchronous serial data
transmission.  These flags may not make sense for other kinds of
terminal ports (such as a network connection pseudo-terminal).  All of
these are contained in the @code{c_cflag} member of the @code{struct
termios} structure.

The @code{c_cflag} member itself is an integer, and you change the flags
and fields using the operators @code{&}, @code{|}, and @code{^}.  Don't
try to specify the entire value for @code{c_cflag}---instead, change
only specific flags and leave the rest untouched (@pxref{Setting
Modes}).

@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t CLOCAL
If this bit is set, it indicates that the terminal is connected
``locally'' and that the modem status lines (such as carrier detect)
should be ignored.
@cindex modem status lines
@cindex carrier detect

On many systems if this bit is not set and you call @code{open} without
the @code{O_NONBLOCK} flag set, @code{open} blocks until a modem
connection is established.

If this bit is not set and a modem disconnect is detected, a
@code{SIGHUP} signal is sent to the controlling process group for the
terminal (if it has one).  Normally, this causes the process to exit;
see @ref{Signal Handling}.  Reading from the terminal after a disconnect
causes an end-of-file condition, and writing causes an @code{EIO} error
to be returned.  The terminal device must be closed and reopened to
clear the condition.
@cindex modem disconnect
@end deftypevr

@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t HUPCL
If this bit is set, a modem disconnect is generated when all processes
that have the terminal device open have either closed the file or exited.
@end deftypevr

@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t CREAD
If this bit is set, input can be read from the terminal.  Otherwise,
input is discarded when it arrives.
@end deftypevr

@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t CSTOPB
If this bit is set, two stop bits are used.  Otherwise, only one stop bit
is used.
@end deftypevr

@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t PARENB
If this bit is set, generation and detection of a parity bit are enabled.
@xref{Input Modes}, for information on how input parity errors are handled.

If this bit is not set, no parity bit is added to output characters, and
input characters are not checked for correct parity.
@end deftypevr

@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t PARODD
This bit is only useful if @code{PARENB} is set.  If @code{PARODD} is set,
odd parity is used, otherwise even parity is used.
@end deftypevr

The control mode flags also includes a field for the number of bits per
character.  You can use the @code{CSIZE} macro as a mask to extract the
value, like this: @code{settings.c_cflag & CSIZE}.

@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t CSIZE
This is a mask for the number of bits per character.
@end deftypevr

@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t CS5
This specifies five bits per byte.
@end deftypevr

@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t CS6
This specifies six bits per byte.
@end deftypevr

@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t CS7
This specifies seven bits per byte.
@end deftypevr

@comment termios.h
@comment POSIX.1
@deftypevr Macro tcflag_t CS8