оконечное устройство (terminal device)
Пролог (Prolog)
This manual page is part of the POSIX Programmer's Manual. The
Linux implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
Имя (Name)
posix_openpt — open a pseudo-terminal device
Синопсис (Synopsis)
#include <stdlib.h>
#include <fcntl.h>
int posix_openpt(int oflag);
Описание (Description)
The posix_openpt() function shall establish a connection between
a master device for a pseudo-terminal and a file descriptor. The
file descriptor shall be allocated as described in Section 2.14,
File Descriptor Allocation and can be used by other I/O functions
that refer to that pseudo-terminal.
The file status flags and file access modes of the open file
description shall be set according to the value of oflag.
Values for oflag are constructed by a bitwise-inclusive OR of
flags from the following list, defined in <fcntl.h>:
O_RDWR Open for reading and writing.
O_NOCTTY If set posix_openpt() shall not cause the terminal
device to become the controlling terminal for the
process.
The behavior of other values for the oflag argument is
unspecified.
Возвращаемое значение (Return value)
Upon successful completion, the posix_openpt() function shall
open a file descriptor for a master pseudo-terminal device and
return a non-negative integer representing the file descriptor.
Otherwise, -1 shall be returned and errno set to indicate the
error.
Ошибки (Error)
The posix_openpt() function shall fail if:
EMFILE All file descriptors available to the process are
currently open.
ENFILE The maximum allowable number of files is currently open in
the system.
The posix_openpt() function may fail if:
EINVAL The value of oflag is not valid.
EAGAIN Out of pseudo-terminal resources.
ENOSR Out of STREAMS resources.
The following sections are informative.
Примеры (Examples)
Opening a Pseudo-Terminal and Returning the Name of the Slave Device
and a File Descriptor
#include <fcntl.h>
#include <stdio.h>
int masterfd, slavefd;
char *slavedevice;
masterfd = posix_openpt(O_RDWR|O_NOCTTY);
if (masterfd == -1
|| grantpt (masterfd) == -1
|| unlockpt (masterfd) == -1
|| (slavedevice = ptsname (masterfd)) == NULL)
return -1;
printf("slave device is: %s\n", slavedevice);
slavefd = open(slavedevice, O_RDWR|O_NOCTTY);
if (slavefd < 0)
return -1;
Использование в приложениях (Application usage)
This function is a method for portably obtaining a file
descriptor of a master terminal device for a pseudo-terminal. The
grantpt() and ptsname() functions can be used to manipulate mode
and ownership permissions, and to obtain the name of the slave
device, respectively.
Обоснование (Rationale)
The standard developers considered the matter of adding a special
device for cloning master pseudo-terminals: the /dev/ptmx device.
However, consensus could not be reached, and it was felt that
adding a new function would permit other implementations. The
posix_openpt() function is designed to complement the grantpt(),
ptsname(), and unlockpt() functions.
On implementations supporting the /dev/ptmx clone device, opening
the master device of a pseudo-terminal is simply:
mfdp = open("/dev/ptmx", oflag );
if (mfdp < 0)
return -1;
Будущие направления (Future directions)
None.
Смотри также (See also)
Section 2.14, File Descriptor Allocation, grantpt(3p), open(3p),
ptsname(3p), unlockpt(3p)
The Base Definitions volume of POSIX.1‐2017, fcntl.h(0p),
stdlib.h(0p)
