Advanced Programming in the UNIX® Environment

ptg10805159

Appendix C Chapter 18 Solutions 943

if ((cmptr = calloc(1, CMSG_LEN(2*sizeof(int)))) == NULL)

err_sys("calloc error");

msg.msg_control = cmptr;

msg.msg_controllen = CMSG_LEN(2*sizeof(int));

/* continue initializing msghdr... */

cmptr->cmsg_len = CMSG_LEN(2*sizeof(int));

cmptr->cmsg_level = SOL_SOCKET;

cmptr->cmsg_type = SCM_RIGHTS;

ip = (int *)CMSG_DATA(cmptr);

*ip++ = fd1;

*ip = fd2;

This approach works on all four platforms covered in this book. The second

option is to pack two separatecmsghdrstructures into a single message:

struct msghdr msg;

struct cmsghdr *cmptr;

if ((cmptr = calloc(1, 2*CMSG_LEN(sizeof(int)))) == NULL)

err_sys("calloc error");

msg.msg_control = cmptr;

msg.msg_controllen = 2*CMSG_LEN(sizeof(int));

/* continue initializing msghdr... */

cmptr->cmsg_len = CMSG_LEN(sizeof(int));

cmptr->cmsg_level = SOL_SOCKET;

cmptr->cmsg_type = SCM_RIGHTS;

*(int *)CMSG_DATA(cmptr) = fd1;

cmptr = CMPTR_NXTHDR(&msg, cmptr);

cmptr->cmsg_len = CMSG_LEN(sizeof(int));

cmptr->cmsg_level = SOL_SOCKET;

cmptr->cmsg_type = SCM_RIGHTS;

*(int *)CMSG_DATA(cmptr) = fd2;

Unlike the first approach, this method works only on FreeBSD 8.0.

Chapter 18

18.1 Note that you have to terminate theresetcommand with a line feed character,

not a return, since the terminal is in noncanonical mode.

18.2 It builds a table for each of the 128 characters and sets the high-order bit (the

parity bit) according to the user ’s specification. It then uses 8-bit I/O, handling

the parity generation itself.

18.3 If you happen to be on a windowing terminal, you don’t need to log in twice.

Youcan do this experiment between two separate windows. Under Solaris,

execute stty -a with standardinput redirected from the terminal window

runningvi.This shows thatvisets MIN to 1 and TIME to 1.Acall toreadwill

wait for at least one character to be typed, but after that character is entered,

readwaits only one-tenth of a second for additional characters beforereturning.