Advanced Programming in the UNIX® Environment

ptg10805159

Section 17.2 UNIX Domain Sockets 633

#include "apue.h"

#include <sys/msg.h>

#define MAXMSZ 512

struct mymesg {

long mtype;

char mtext[MAXMSZ];

};

int

main(int argc, char *argv[])

{

key_t key;

long qid;

size_t nbytes;

struct mymesg m;

if (argc != 3) {

fprintf(stderr, "usage: sendmsg KEY message\n");

exit(1);

}

key = strtol(argv[1], NULL, 0);

if ((qid = msgget(key, 0)) < 0)

err_sys("can’t open queue key %s", argv[1]);

memset(&m, 0, sizeof(m));

strncpy(m.mtext, argv[2], MAXMSZ-1);

nbytes = strlen(m.mtext);

m.mtype = 1;

if (msgsnd(qid, &m, nbytes, 0) < 0)

err_sys("can’t send message");

exit(0);

}

Figure 17.4 Post a message to an XSI message queue

This program takes two arguments: the key associated with the queue and a string

to be sent as the body of the message. When we send messages to the server, it prints

them as shown below.

$./pollmsg & run the server in the background

[1] 12814

$queue ID 0 is 196608

queue ID 1 is 196609

queue ID 2 is 196610

$./sendmsg 0x123 "hello, world" send a message to the first queue

queue id 196608, message hello, world

$./sendmsg 0x124 "just a test" send a message to the second queue

queue id 196609, message just a test

$./sendmsg 0x125 "bye" send a message to the third queue

queue id 196610, message bye