Advanced Programming in the UNIX® Environment

ptg10805159

694 Te rminal I/O Chapter 18

Thetcsendbreak function transmits a continuous stream of zerobits for a

specified duration. If thedurationargument is 0, the transmission lasts between 0.25

second and 0.5 second. POSIX.1 specifies that ifdurationis nonzero, the transmission

time is implementation dependent.

18.9 Ter minal Identification

Historically,the name of the controlling terminal in most versions of the UNIX System

has been/dev/tty.POSIX.1 provides a runtime function that we can call to determine

the name of the controlling terminal.

#include <stdio.h>

char *ctermid(char *ptr);

Returns: pointer to name of controlling terminal

on success, pointer to empty string on error

Ifptris non-null, it is assumed to point to an array of at leastL_ctermidbytes, and the

name of the controlling terminal of the process is stored in the array.The constant

L_ctermidis defined in<stdio.h>.Ifptris a null pointer,the function allocates

room for the array (usually as a static variable). Again, the name of the controlling

terminal of the process is stored in the array.

In both cases, the starting address of the array is returned as the value of the

function. Since most UNIX systems use/dev/ttyas the name of the controlling

terminal, this function is intended to aid portability to other operating systems.

All four platforms described in this text return the string/dev/ttywhen we callctermid.

Example —ctermidFunction

Figure18.12 shows an implementation of the POSIX.1ctermidfunction.

#include <stdio.h>

#include <string.h>

static char ctermid_name[L_ctermid];

char *

ctermid(char *str)

{

if (str == NULL)

str = ctermid_name;

return(strcpy(str, "/dev/tty")); /* strcpy() returns str */

}

Figure 18.12Implementation of POSIX.1ctermidfunction