posix_openpt() — Open a pseudo-terminal device

Standards

Standards / Extensions	C or C++	Dependencies
Single UNIX Specification, Version 3	both	z/OS® V1.9

Format

#define _XOPEN_SOURCE 600 
#include <stdlib.h>
#include <fcntl.h>

int posix_openpt(int oflag);

General description

The posix_openpt() function establishes a connection between a master device for a pseudo-terminal and a file descriptor. The file descriptor is 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 are 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() will not cause the terminal device to become the controlling terminal for the process.

The behavior of other values for the oflag argument is unspecified.

Argument: Description
oflag: The value of the file status flags and file access modes |of the open file description.

Returned value

Upon successful completion, the posix_openpt() function opens a master pseudo-terminal device and returns a non-negative integer representing the lowest numbered unused file descriptor. Otherwise, -1 is returned and errno set to indicate the error.

Error Code: Description
EMFILE: {OPEN_MAX} file descriptors are currently open in the calling process.
ENFILE: The maximum allowable number of files is currently open in the system.
EINVAL: The value of oflag is not valid.
EAGAIN: Out of pseudo-terminal resources.

Example

CELEBP71

/* CELEBP71

   This example demonstrates how to use posix_openpt() to open a
   master psuedo-terminal device.

   Expected output:
   The master psuedo-terminal id is [first available descriptor]

*/
#define _XOPEN_SOURCE 600
#include <stdlib.h>
#include <fcntl.h>
#include <stdio.h>

void main() {
   int fd;

   fd = posix_openpt(O_RDWR | O_NOCTTY);
   if (fd == -1)
      perror("Error opening a terminal.\n");
   else
      printf("The master psuedo-terminal id is %d\n",fd);
}