This is libc.info, produced by makeinfo version 4.2 from libc.texinfo. INFO-DIR-SECTION GNU libraries START-INFO-DIR-ENTRY * Libc: (libc). C library. END-INFO-DIR-ENTRY This file documents the GNU C library. This is Edition 0.10, last updated 2001-07-06, of `The GNU C Library Reference Manual', for Version 2.3.x. Copyright (C) 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2001, 2002 Free Software Foundation, Inc. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.1 or any later version published by the Free Software Foundation; with the Invariant Sections being "Free Software Needs Free Documentation" and "GNU Lesser General Public License", the Front-Cover texts being (a) (see below), and with the Back-Cover Texts being (b) (see below). A copy of the license is included in the section entitled "GNU Free Documentation License". (a) The FSF's Front-Cover Text is: A GNU Manual (b) The FSF's Back-Cover Text is: You have freedom to copy and modify this GNU Manual, like GNU software. Copies published by the Free Software Foundation raise funds for GNU development.  File: libc.info, Node: Socket Option Functions, Next: Socket-Level Options, Up: Socket Options Socket Option Functions ----------------------- Here are the functions for examining and modifying socket options. They are declared in `sys/socket.h'. - Function: int getsockopt (int SOCKET, int LEVEL, int OPTNAME, void *OPTVAL, socklen_t *OPTLEN-PTR) The `getsockopt' function gets information about the value of option OPTNAME at level LEVEL for socket SOCKET. The option value is stored in a buffer that OPTVAL points to. Before the call, you should supply in `*OPTLEN-PTR' the size of this buffer; on return, it contains the number of bytes of information actually stored in the buffer. Most options interpret the OPTVAL buffer as a single `int' value. The actual return value of `getsockopt' is `0' on success and `-1' on failure. The following `errno' error conditions are defined: `EBADF' The SOCKET argument is not a valid file descriptor. `ENOTSOCK' The descriptor SOCKET is not a socket. `ENOPROTOOPT' The OPTNAME doesn't make sense for the given LEVEL. - Function: int setsockopt (int SOCKET, int LEVEL, int OPTNAME, void *OPTVAL, socklen_t OPTLEN) This function is used to set the socket option OPTNAME at level LEVEL for socket SOCKET. The value of the option is passed in the buffer OPTVAL of size OPTLEN. The return value and error codes for `setsockopt' are the same as for `getsockopt'.  File: libc.info, Node: Socket-Level Options, Prev: Socket Option Functions, Up: Socket Options Socket-Level Options -------------------- - Constant: int SOL_SOCKET Use this constant as the LEVEL argument to `getsockopt' or `setsockopt' to manipulate the socket-level options described in this section. Here is a table of socket-level option names; all are defined in the header file `sys/socket.h'. `SO_DEBUG' This option toggles recording of debugging information in the underlying protocol modules. The value has type `int'; a nonzero value means "yes". `SO_REUSEADDR' This option controls whether `bind' (*note Setting Address::) should permit reuse of local addresses for this socket. If you enable this option, you can actually have two sockets with the same Internet port number; but the system won't allow you to use the two identically-named sockets in a way that would confuse the Internet. The reason for this option is that some higher-level Internet protocols, including FTP, require you to keep reusing the same port number. The value has type `int'; a nonzero value means "yes". `SO_KEEPALIVE' This option controls whether the underlying protocol should periodically transmit messages on a connected socket. If the peer fails to respond to these messages, the connection is considered broken. The value has type `int'; a nonzero value means "yes". `SO_DONTROUTE' This option controls whether outgoing messages bypass the normal message routing facilities. If set, messages are sent directly to the network interface instead. The value has type `int'; a nonzero value means "yes". `SO_LINGER' This option specifies what should happen when the socket of a type that promises reliable delivery still has untransmitted messages when it is closed; see *Note Closing a Socket::. The value has type `struct linger'. - Data Type: struct linger This structure type has the following members: `int l_onoff' This field is interpreted as a boolean. If nonzero, `close' blocks until the data are transmitted or the timeout period has expired. `int l_linger' This specifies the timeout period, in seconds. `SO_BROADCAST' This option controls whether datagrams may be broadcast from the socket. The value has type `int'; a nonzero value means "yes". `SO_OOBINLINE' If this option is set, out-of-band data received on the socket is placed in the normal input queue. This permits it to be read using `read' or `recv' without specifying the `MSG_OOB' flag. *Note Out-of-Band Data::. The value has type `int'; a nonzero value means "yes". `SO_SNDBUF' This option gets or sets the size of the output buffer. The value is a `size_t', which is the size in bytes. `SO_RCVBUF' This option gets or sets the size of the input buffer. The value is a `size_t', which is the size in bytes. `SO_STYLE' `SO_TYPE' This option can be used with `getsockopt' only. It is used to get the socket's communication style. `SO_TYPE' is the historical name, and `SO_STYLE' is the preferred name in GNU. The value has type `int' and its value designates a communication style; see *Note Communication Styles::. `SO_ERROR' This option can be used with `getsockopt' only. It is used to reset the error status of the socket. The value is an `int', which represents the previous error status.  File: libc.info, Node: Networks Database, Prev: Socket Options, Up: Sockets Networks Database ================= Many systems come with a database that records a list of networks known to the system developer. This is usually kept either in the file `/etc/networks' or in an equivalent from a name server. This data base is useful for routing programs such as `route', but it is not useful for programs that simply communicate over the network. We provide functions to access this database, which are declared in `netdb.h'. - Data Type: struct netent This data type is used to represent information about entries in the networks database. It has the following members: `char *n_name' This is the "official" name of the network. `char **n_aliases' These are alternative names for the network, represented as a vector of strings. A null pointer terminates the array. `int n_addrtype' This is the type of the network number; this is always equal to `AF_INET' for Internet networks. `unsigned long int n_net' This is the network number. Network numbers are returned in host byte order; see *Note Byte Order::. Use the `getnetbyname' or `getnetbyaddr' functions to search the networks database for information about a specific network. The information is returned in a statically-allocated structure; you must copy the information if you need to save it. - Function: struct netent * getnetbyname (const char *NAME) The `getnetbyname' function returns information about the network named NAME. It returns a null pointer if there is no such network. - Function: struct netent * getnetbyaddr (unsigned long int NET, int TYPE) The `getnetbyaddr' function returns information about the network of type TYPE with number NET. You should specify a value of `AF_INET' for the TYPE argument for Internet networks. `getnetbyaddr' returns a null pointer if there is no such network. You can also scan the networks database using `setnetent', `getnetent' and `endnetent'. Be careful when using these functions because they are not reentrant. - Function: void setnetent (int STAYOPEN) This function opens and rewinds the networks database. If the STAYOPEN argument is nonzero, this sets a flag so that subsequent calls to `getnetbyname' or `getnetbyaddr' will not close the database (as they usually would). This makes for more efficiency if you call those functions several times, by avoiding reopening the database for each call. - Function: struct netent * getnetent (void) This function returns the next entry in the networks database. It returns a null pointer if there are no more entries. - Function: void endnetent (void) This function closes the networks database.  File: libc.info, Node: Low-Level Terminal Interface, Next: Syslog, Prev: Sockets, Up: Top Low-Level Terminal Interface **************************** This chapter describes functions that are specific to terminal devices. You can use these functions to do things like turn off input echoing; set serial line characteristics such as line speed and flow control; and change which characters are used for end-of-file, command-line editing, sending signals, and similar control functions. Most of the functions in this chapter operate on file descriptors. *Note Low-Level I/O::, for more information about what a file descriptor is and how to open a file descriptor for a terminal device. * Menu: * Is It a Terminal:: How to determine if a file is a terminal device, and what its name is. * I/O Queues:: About flow control and typeahead. * Canonical or Not:: Two basic styles of input processing. * Terminal Modes:: How to examine and modify flags controlling details of terminal I/O: echoing, signals, editing. Posix. * BSD Terminal Modes:: BSD compatible terminal mode setting * Line Control:: Sending break sequences, clearing terminal buffers ... * Noncanon Example:: How to read single characters without echo. * Pseudo-Terminals:: How to open a pseudo-terminal.  File: libc.info, Node: Is It a Terminal, Next: I/O Queues, Up: Low-Level Terminal Interface Identifying Terminals ===================== The functions described in this chapter only work on files that correspond to terminal devices. You can find out whether a file descriptor is associated with a terminal by using the `isatty' function. Prototypes for the functions in this section are declared in the header file `unistd.h'. - Function: int isatty (int FILEDES) This function returns `1' if FILEDES is a file descriptor associated with an open terminal device, and 0 otherwise. If a file descriptor is associated with a terminal, you can get its associated file name using the `ttyname' function. See also the `ctermid' function, described in *Note Identifying the Terminal::. - Function: char * ttyname (int FILEDES) If the file descriptor FILEDES is associated with a terminal device, the `ttyname' function returns a pointer to a statically-allocated, null-terminated string containing the file name of the terminal file. The value is a null pointer if the file descriptor isn't associated with a terminal, or the file name cannot be determined. - Function: int ttyname_r (int FILEDES, char *BUF, size_t LEN) The `ttyname_r' function is similar to the `ttyname' function except that it places its result into the user-specified buffer starting at BUF with length LEN. The normal return value from `ttyname_r' is 0. Otherwise an error number is returned to indicate the error. The following `errno' error conditions are defined for this function: `EBADF' The FILEDES argument is not a valid file descriptor. `ENOTTY' The FILEDES is not associated with a terminal. `ERANGE' The buffer length LEN is too small to store the string to be returned.  File: libc.info, Node: I/O Queues, Next: Canonical or Not, Prev: Is It a Terminal, Up: Low-Level Terminal Interface I/O Queues ========== Many of the remaining functions in this section refer to the input and output queues of a terminal device. These queues implement a form of buffering _within the kernel_ independent of the buffering implemented by I/O streams (*note I/O on Streams::). The "terminal input queue" is also sometimes referred to as its "typeahead buffer". It holds the characters that have been received from the terminal but not yet read by any process. The size of the input queue is described by the `MAX_INPUT' and `_POSIX_MAX_INPUT' parameters; see *Note Limits for Files::. You are guaranteed a queue size of at least `MAX_INPUT', but the queue might be larger, and might even dynamically change size. If input flow control is enabled by setting the `IXOFF' input mode bit (*note Input Modes::), the terminal driver transmits STOP and START characters to the terminal when necessary to prevent the queue from overflowing. Otherwise, input may be lost if it comes in too fast from the terminal. In canonical mode, all input stays in the queue until a newline character is received, so the terminal input queue can fill up when you type a very long line. *Note Canonical or Not::. The "terminal output queue" is like the input queue, but for output; it contains characters that have been written by processes, but not yet transmitted to the terminal. If output flow control is enabled by setting the `IXON' input mode bit (*note Input Modes::), the terminal driver obeys START and STOP characters sent by the terminal to stop and restart transmission of output. "Clearing" the terminal input queue means discarding any characters that have been received but not yet read. Similarly, clearing the terminal output queue means discarding any characters that have been written but not yet transmitted.  File: libc.info, Node: Canonical or Not, Next: Terminal Modes, Prev: I/O Queues, Up: Low-Level Terminal Interface Two Styles of Input: Canonical or Not ===================================== POSIX systems support two basic modes of input: canonical and noncanonical. In "canonical input processing" mode, terminal input is processed in lines terminated by newline (`'\n''), EOF, or EOL characters. No input can be read until an entire line has been typed by the user, and the `read' function (*note I/O Primitives::) returns at most a single line of input, no matter how many bytes are requested. In canonical input mode, the operating system provides input editing facilities: some characters are interpreted specially to perform editing operations within the current line of text, such as ERASE and KILL. *Note Editing Characters::. The constants `_POSIX_MAX_CANON' and `MAX_CANON' parameterize the maximum number of bytes which may appear in a single line of canonical input. *Note Limits for Files::. You are guaranteed a maximum line length of at least `MAX_CANON' bytes, but the maximum might be larger, and might even dynamically change size. In "noncanonical input processing" mode, characters are not grouped into lines, and ERASE and KILL processing is not performed. The granularity with which bytes are read in noncanonical input mode is controlled by the MIN and TIME settings. *Note Noncanonical Input::. Most programs use canonical input mode, because this gives the user a way to edit input line by line. The usual reason to use noncanonical mode is when the program accepts single-character commands or provides its own editing facilities. The choice of canonical or noncanonical input is controlled by the `ICANON' flag in the `c_lflag' member of `struct termios'. *Note Local Modes::.  File: libc.info, Node: Terminal Modes, Next: BSD Terminal Modes, Prev: Canonical or Not, Up: Low-Level Terminal Interface Terminal Modes ============== This section describes the various terminal attributes that control how input and output are done. The functions, data structures, and symbolic constants are all declared in the header file `termios.h'. Don't confuse terminal attributes with file attributes. A device special file which is associated with a terminal has file attributes as described in *Note File Attributes::. These are unrelated to the attributes of the terminal device itself, which are discussed in this section. * Menu: * Mode Data Types:: The data type `struct termios' and related types. * Mode Functions:: Functions to read and set the terminal attributes. * Setting Modes:: The right way to set terminal attributes reliably. * Input Modes:: Flags controlling low-level input handling. * Output Modes:: Flags controlling low-level output handling. * Control Modes:: Flags controlling serial port behavior. * Local Modes:: Flags controlling high-level input handling. * Line Speed:: How to read and set the terminal line speed. * Special Characters:: Characters that have special effects, and how to change them. * Noncanonical Input:: Controlling how long to wait for input.  File: libc.info, Node: Mode Data Types, Next: Mode Functions, Up: Terminal Modes Terminal Mode Data Types ------------------------ The entire collection of attributes of a terminal is stored in a structure of type `struct termios'. This structure is used with the functions `tcgetattr' and `tcsetattr' to read and set the attributes. - Data Type: struct termios Structure that records all the I/O attributes of a terminal. The structure includes at least the following members: `tcflag_t c_iflag' A bit mask specifying flags for input modes; see *Note Input Modes::. `tcflag_t c_oflag' A bit mask specifying flags for output modes; see *Note Output Modes::. `tcflag_t c_cflag' A bit mask specifying flags for control modes; see *Note Control Modes::. `tcflag_t c_lflag' A bit mask specifying flags for local modes; see *Note Local Modes::. `cc_t c_cc[NCCS]' An array specifying which characters are associated with various control functions; see *Note Special Characters::. The `struct termios' structure also contains members which encode input and output transmission speeds, but the representation is not specified. *Note Line Speed::, for how to examine and store the speed values. The following sections describe the details of the members of the `struct termios' structure. - Data Type: tcflag_t This is an unsigned integer type used to represent the various bit masks for terminal flags. - Data Type: cc_t This is an unsigned integer type used to represent characters associated with various terminal control functions. - Macro: int NCCS The value of this macro is the number of elements in the `c_cc' array.  File: libc.info, Node: Mode Functions, Next: Setting Modes, Prev: Mode Data Types, Up: Terminal Modes Terminal Mode Functions ----------------------- - Function: int tcgetattr (int FILEDES, struct termios *TERMIOS-P) This function is used to examine the attributes of the terminal device with file descriptor FILEDES. The attributes are returned in the structure that TERMIOS-P points to. If successful, `tcgetattr' returns 0. A return value of -1 indicates an error. The following `errno' error conditions are defined for this function: `EBADF' The FILEDES argument is not a valid file descriptor. `ENOTTY' The FILEDES is not associated with a terminal. - Function: int tcsetattr (int FILEDES, int WHEN, const struct termios *TERMIOS-P) This function sets the attributes of the terminal device with file descriptor FILEDES. The new attributes are taken from the structure that TERMIOS-P points to. The WHEN argument specifies how to deal with input and output already queued. It can be one of the following values: `TCSANOW' Make the change immediately. `TCSADRAIN' Make the change after waiting until all queued output has been written. You should usually use this option when changing parameters that affect output. `TCSAFLUSH' This is like `TCSADRAIN', but also discards any queued input. `TCSASOFT' 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. Using `TCSASOFT' is exactly the same as setting the `CIGNORE' bit in the `c_cflag' member of the structure TERMIOS-P points to. *Note Control Modes::, for a description of `CIGNORE'. If this function is called from a background process on its controlling terminal, normally all processes in the process group are sent a `SIGTTOU' 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 `SIGTTOU' signals, in which case the operation is performed and no signal is sent. *Note Job Control::. If successful, `tcsetattr' returns 0. A return value of -1 indicates an error. The following `errno' error conditions are defined for this function: `EBADF' The FILEDES argument is not a valid file descriptor. `ENOTTY' The FILEDES is not associated with a terminal. `EINVAL' Either the value of the `when' argument is not valid, or there is something wrong with the data in the TERMIOS-P argument. Although `tcgetattr' and `tcsetattr' 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. 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.  File: libc.info, Node: Setting Modes, Next: Input Modes, Prev: Mode Functions, Up: Terminal Modes Setting Terminal Modes Properly ------------------------------- When you set terminal modes, you should call `tcgetattr' first to get the current modes of the particular terminal device, modify only those modes that you are really interested in, and store the result with `tcsetattr'. It's a bad idea to simply initialize a `struct termios' structure to a chosen set of attributes and pass it directly to `tcsetattr'. Your program may be run years from now, on systems that support members not documented in this manual. The way to avoid setting these members to unreasonable values is to avoid changing them. What's more, different terminal devices may require different mode settings in order to function properly. So you should avoid blindly copying attributes from one terminal device to another. When a member contains a collection of independent flags, as the `c_iflag', `c_oflag' and `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 (`ISTRIP') in the `struct termios' structure while properly preserving all the other data in the structure: int set_istrip (int desc, int value) { struct termios settings; int result; result = tcgetattr (desc, &settings); if (result < 0) { perror ("error in tcgetattr"); return 0; } settings.c_iflag &= ~ISTRIP; if (value) settings.c_iflag |= ISTRIP; result = tcsetattr (desc, TCSANOW, &settings); if (result < 0) { perror ("error in tcsetattr"); return 0; } return 1; }  File: libc.info, Node: Input Modes, Next: Output Modes, Prev: Setting Modes, Up: Terminal Modes 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 and characters. All of these flags are bits in the `c_iflag' member of the `struct termios' structure. The member is an integer, and you change flags using the operators `&', `|' and `^'. Don't try to specify the entire value for `c_iflag'--instead, change only specific flags and leave the rest untouched (*note Setting Modes::). - Macro: tcflag_t INPCK 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 *Note Control Modes::. For example, you could clear the `INPCK' input mode flag and set the `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 `IGNPAR' or `PARMRK' bits are set. If neither of these bits are set, a byte with a parity error is passed to the application as a `'\0'' character. - Macro: tcflag_t IGNPAR If this bit is set, any byte with a framing or parity error is ignored. This is only useful if `INPCK' is also set. - 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 `INPCK' is set and `IGNPAR' is not set. The way erroneous bytes are marked is with two preceding bytes, `377' and `0'. Thus, the program actually reads three bytes for one erroneous byte received from the terminal. If a valid byte has the value `0377', and `ISTRIP' (see below) is not set, the program might confuse it with the prefix that marks a parity error. So a valid byte `0377' is passed to the program as two bytes, `0377' `0377', in this case. - 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. - Macro: tcflag_t IGNBRK If this bit is set, break conditions are ignored. A "break condition" is defined in the context of asynchronous serial data transmission as a series of zero-value bits longer than a single byte. - Macro: tcflag_t BRKINT If this bit is set and `IGNBRK' is not set, a break condition clears the terminal input and output queues and raises a `SIGINT' signal for the foreground process group associated with the terminal. If neither `BRKINT' nor `IGNBRK' are set, a break condition is passed to the application as a single `'\0'' character if `PARMRK' is not set, or otherwise as a three-character sequence `'\377'', `'\0'', `'\0''. - Macro: tcflag_t IGNCR If this bit is set, carriage return characters (`'\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. - Macro: tcflag_t ICRNL If this bit is set and `IGNCR' is not set, carriage return characters (`'\r'') received as input are passed to the application as newline characters (`'\n''). - Macro: tcflag_t INLCR If this bit is set, newline characters (`'\n'') received as input are passed to the application as carriage return characters (`'\r''). - 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. *Note Start/Stop Characters::. - 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. *Note Start/Stop Characters::. - 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. - Macro: tcflag_t IMAXBEL If this bit is set, then filling up the terminal input buffer sends a BEL character (code `007') to the terminal to ring the bell. This is a BSD extension.  File: libc.info, Node: Output Modes, Next: Control Modes, Prev: Input Modes, Up: Terminal Modes 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 `c_oflag' member of the `struct termios' structure. The `c_oflag' member itself is an integer, and you change the flags and fields using the operators `&', `|', and `^'. Don't try to specify the entire value for `c_oflag'--instead, change only specific flags and leave the rest untouched (*note Setting Modes::). - 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 (`'\n'') onto carriage return and linefeed pairs. If this bit isn't set, the characters are transmitted as-is. The following three bits are BSD features, and they exist only BSD systems and the GNU system. They are effective only if `OPOST' is set. - 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. - 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. - Macro: tcflag_t ONOEOT If this bit is set, discard `C-d' characters (code `004') on output. These characters cause many dial-up terminals to disconnect.  File: libc.info, Node: Control Modes, Next: Local Modes, Prev: Output Modes, Up: Terminal Modes 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 `c_cflag' member of the `struct termios' structure. The `c_cflag' member itself is an integer, and you change the flags and fields using the operators `&', `|', and `^'. Don't try to specify the entire value for `c_cflag'--instead, change only specific flags and leave the rest untouched (*note Setting Modes::). - 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. On many systems if this bit is not set and you call `open' without the `O_NONBLOCK' flag set, `open' blocks until a modem connection is established. If this bit is not set and a modem disconnect is detected, a `SIGHUP' signal is sent to the controlling process group for the terminal (if it has one). Normally, this causes the process to exit; see *Note Signal Handling::. Reading from the terminal after a disconnect causes an end-of-file condition, and writing causes an `EIO' error to be returned. The terminal device must be closed and reopened to clear the condition. - 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. - Macro: tcflag_t CREAD If this bit is set, input can be read from the terminal. Otherwise, input is discarded when it arrives. - Macro: tcflag_t CSTOPB If this bit is set, two stop bits are used. Otherwise, only one stop bit is used. - Macro: tcflag_t PARENB If this bit is set, generation and detection of a parity bit are enabled. *Note 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. - Macro: tcflag_t PARODD This bit is only useful if `PARENB' is set. If `PARODD' is set, odd parity is used, otherwise even parity is used. The control mode flags also includes a field for the number of bits per character. You can use the `CSIZE' macro as a mask to extract the value, like this: `settings.c_cflag & CSIZE'. - Macro: tcflag_t CSIZE This is a mask for the number of bits per character. - Macro: tcflag_t CS5 This specifies five bits per byte. - Macro: tcflag_t CS6 This specifies six bits per byte. - Macro: tcflag_t CS7 This specifies seven bits per byte. - Macro: tcflag_t CS8 This specifies eight bits per byte. The following four bits are BSD extensions; this exist only on BSD systems and the GNU system. - Macro: tcflag_t CCTS_OFLOW If this bit is set, enable flow control of output based on the CTS wire (RS232 protocol). - Macro: tcflag_t CRTS_IFLOW If this bit is set, enable flow control of input based on the RTS wire (RS232 protocol). - Macro: tcflag_t MDMBUF If this bit is set, enable carrier-based flow control of output. - Macro: tcflag_t CIGNORE If this bit is set, it says to ignore the control modes and line speed values entirely. This is only meaningful in a call to `tcsetattr'. The `c_cflag' member and the line speed values returned by `cfgetispeed' and `cfgetospeed' will be unaffected by the call. `CIGNORE' is useful if you want to set all the software modes in the other members, but leave the hardware details in `c_cflag' unchanged. (This is how the `TCSASOFT' flag to `tcsettattr' works.) This bit is never set in the structure filled in by `tcgetattr'.  File: libc.info, Node: Local Modes, Next: Line Speed, Prev: Control Modes, Up: Terminal Modes Local Modes ----------- This section describes the flags for the `c_lflag' member of the `struct termios' structure. These flags generally control higher-level aspects of input processing than the input modes flags described in *Note Input Modes::, such as echoing, signals, and the choice of canonical or noncanonical input. The `c_lflag' member itself is an integer, and you change the flags and fields using the operators `&', `|', and `^'. Don't try to specify the entire value for `c_lflag'--instead, change only specific flags and leave the rest untouched (*note Setting Modes::). - Macro: tcflag_t ICANON This bit, if set, enables canonical input processing mode. Otherwise, input is processed in noncanonical mode. *Note Canonical or Not::. - Macro: tcflag_t ECHO If this bit is set, echoing of input characters back to the terminal is enabled. - Macro: tcflag_t ECHOE If this bit is set, echoing indicates erasure of input with the ERASE character by erasing the last character in the current line from the screen. Otherwise, the character erased is re-echoed to show what has happened (suitable for a printing terminal). This bit only controls the display behavior; the `ICANON' bit by itself controls actual recognition of the ERASE character and erasure of input, without which `ECHOE' is simply irrelevant. - Macro: tcflag_t ECHOPRT This bit is like `ECHOE', enables display of the ERASE character in a way that is geared to a hardcopy terminal. When you type the ERASE character, a `\' character is printed followed by the first character erased. Typing the ERASE character again just prints the next character erased. Then, the next time you type a normal character, a `/' character is printed before the character echoes. This is a BSD extension, and exists only in BSD systems and the GNU system. - Macro: tcflag_t ECHOK This bit enables special display of the KILL character by moving to a new line after echoing the KILL character normally. The behavior of `ECHOKE' (below) is nicer to look at. If this bit is not set, the KILL character echoes just as it would if it were not the KILL character. Then it is up to the user to remember that the KILL character has erased the preceding input; there is no indication of this on the screen. This bit only controls the display behavior; the `ICANON' bit by itself controls actual recognition of the KILL character and erasure of input, without which `ECHOK' is simply irrelevant. - Macro: tcflag_t ECHOKE This bit is similar to `ECHOK'. It enables special display of the KILL character by erasing on the screen the entire line that has been killed. This is a BSD extension, and exists only in BSD systems and the GNU system. - Macro: tcflag_t ECHONL If this bit is set and the `ICANON' bit is also set, then the newline (`'\n'') character is echoed even if the `ECHO' bit is not set. - Macro: tcflag_t ECHOCTL If this bit is set and the `ECHO' bit is also set, echo control characters with `^' followed by the corresponding text character. Thus, control-A echoes as `^A'. This is usually the preferred mode for interactive input, because echoing a control character back to the terminal could have some undesired effect on the terminal. This is a BSD extension, and exists only in BSD systems and the GNU system. - Macro: tcflag_t ISIG This bit controls whether the INTR, QUIT, and SUSP characters are recognized. The functions associated with these characters are performed if and only if this bit is set. Being in canonical or noncanonical input mode has no affect on the interpretation of these characters. You should use caution when disabling recognition of these characters. Programs that cannot be interrupted interactively are very user-unfriendly. If you clear this bit, your program should provide some alternate interface that allows the user to interactively send the signals associated with these characters, or to escape from the program. *Note Signal Characters::. - Macro: tcflag_t IEXTEN POSIX.1 gives `IEXTEN' implementation-defined meaning, so you cannot rely on this interpretation on all systems. On BSD systems and the GNU system, it enables the LNEXT and DISCARD characters. *Note Other Special::. - Macro: tcflag_t NOFLSH Normally, the INTR, QUIT, and SUSP characters cause input and output queues for the terminal to be cleared. If this bit is set, the queues are not cleared. - Macro: tcflag_t TOSTOP If this bit is set and the system supports job control, then `SIGTTOU' signals are generated by background processes that attempt to write to the terminal. *Note Access to the Terminal::. The following bits are BSD extensions; they exist only in BSD systems and the GNU system. - Macro: tcflag_t ALTWERASE This bit determines how far the WERASE character should erase. The WERASE character erases back to the beginning of a word; the question is, where do words begin? If this bit is clear, then the beginning of a word is a nonwhitespace character following a whitespace character. If the bit is set, then the beginning of a word is an alphanumeric character or underscore following a character which is none of those. *Note Editing Characters::, for more information about the WERASE character. - Macro: tcflag_t FLUSHO This is the bit that toggles when the user types the DISCARD character. While this bit is set, all output is discarded. *Note Other Special::. - Macro: tcflag_t NOKERNINFO Setting this bit disables handling of the STATUS character. *Note Other Special::. - Macro: tcflag_t PENDIN If this bit is set, it indicates that there is a line of input that needs to be reprinted. Typing the REPRINT character sets this bit; the bit remains set until reprinting is finished. *Note Editing Characters::.  File: libc.info, Node: Line Speed, Next: Special Characters, Prev: Local Modes, Up: Terminal Modes Line Speed ---------- The terminal line speed tells the computer how fast to read and write data on the terminal. If the terminal is connected to a real serial line, the terminal speed you specify actually controls the line--if it doesn't match the terminal's own idea of the speed, communication does not work. Real serial ports accept only certain standard speeds. Also, particular hardware may not support even all the standard speeds. Specifying a speed of zero hangs up a dialup connection and turns off modem control signals. If the terminal is not a real serial line (for example, if it is a network connection), then the line speed won't really affect data transmission speed, but some programs will use it to determine the amount of padding needed. It's best to specify a line speed value that matches the actual speed of the actual terminal, but you can safely experiment with different values to vary the amount of padding. There are actually two line speeds for each terminal, one for input and one for output. You can set them independently, but most often terminals use the same speed for both directions. The speed values are stored in the `struct termios' structure, but don't try to access them in the `struct termios' structure directly. Instead, you should use the following functions to read and store them: - Function: speed_t cfgetospeed (const struct termios *TERMIOS-P) This function returns the output line speed stored in the structure `*TERMIOS-P'. - Function: speed_t cfgetispeed (const struct termios *TERMIOS-P) This function returns the input line speed stored in the structure `*TERMIOS-P'. - Function: int cfsetospeed (struct termios *TERMIOS-P, speed_t SPEED) This function stores SPEED in `*TERMIOS-P' as the output speed. The normal return value is 0; a value of -1 indicates an error. If SPEED is not a speed, `cfsetospeed' returns -1. - Function: int cfsetispeed (struct termios *TERMIOS-P, speed_t SPEED) This function stores SPEED in `*TERMIOS-P' as the input speed. The normal return value is 0; a value of -1 indicates an error. If SPEED is not a speed, `cfsetospeed' returns -1. - Function: int cfsetspeed (struct termios *TERMIOS-P, speed_t SPEED) This function stores SPEED in `*TERMIOS-P' as both the input and output speeds. The normal return value is 0; a value of -1 indicates an error. If SPEED is not a speed, `cfsetspeed' returns -1. This function is an extension in 4.4 BSD. - Data Type: speed_t The `speed_t' type is an unsigned integer data type used to represent line speeds. The functions `cfsetospeed' and `cfsetispeed' report errors only for speed values that the system simply cannot handle. If you specify a speed value that is basically acceptable, then those functions will succeed. But they do not check that a particular hardware device can actually support the specified speeds--in fact, they don't know which device you plan to set the speed for. If you use `tcsetattr' to set the speed of a particular device to a value that it cannot handle, `tcsetattr' returns -1. *Portability note:* In the GNU library, the functions above accept speeds measured in bits per second as input, and return speed values measured in bits per second. Other libraries require speeds to be indicated by special codes. For POSIX.1 portability, you must use one of the following symbols to represent the speed; their precise numeric values are system-dependent, but each name has a fixed meaning: `B110' stands for 110 bps, `B300' for 300 bps, and so on. There is no portable way to represent any speed but these, but these are the only speeds that typical serial lines can support. B0 B50 B75 B110 B134 B150 B200 B300 B600 B1200 B1800 B2400 B4800 B9600 B19200 B38400 B57600 B115200 B230400 B460800 BSD defines two additional speed symbols as aliases: `EXTA' is an alias for `B19200' and `EXTB' is an alias for `B38400'. These aliases are obsolete.  File: libc.info, Node: Special Characters, Next: Noncanonical Input, Prev: Line Speed, Up: Terminal Modes Special Characters ------------------ In canonical input, the terminal driver recognizes a number of special characters which perform various control functions. These include the ERASE character (usually ) for editing input, and other editing characters. The INTR character (normally `C-c') for sending a `SIGINT' signal, and other signal-raising characters, may be available in either canonical or noncanonical input mode. All these characters are described in this section. The particular characters used are specified in the `c_cc' member of the `struct termios' structure. This member is an array; each element specifies the character for a particular role. Each element has a symbolic constant that stands for the index of that element--for example, `VINTR' is the index of the element that specifies the INTR character, so storing `'='' in `TERMIOS.c_cc[VINTR]' specifies `=' as the INTR character. On some systems, you can disable a particular special character function by specifying the value `_POSIX_VDISABLE' for that role. This value is unequal to any possible character code. *Note Options for Files::, for more information about how to tell whether the operating system you are using supports `_POSIX_VDISABLE'. * Menu: * Editing Characters:: Special characters that terminate lines and delete text, and other editing functions. * Signal Characters:: Special characters that send or raise signals to or for certain classes of processes. * Start/Stop Characters:: Special characters that suspend or resume suspended output. * Other Special:: Other special characters for BSD systems: they can discard output, and print status.