svmsg/svmsg_send.c

/* svmsg_send.c

   Usage: svmsg_send [-n] msqid msg-type [msg-text]

   Experiment with the msgsnd() system call to send messages to a
   System V message queue.

   See also svmsg_receive.c.
*/
#include <sys/types.h>
#include <sys/msg.h>
#include "tlpi_hdr.h"

#define MAX_MTEXT 1024

struct mbuf {
    long mtype;                         /* Message type */
    char mtext[MAX_MTEXT];              /* Message body */
};

static void             /* Print (optional) message, then usage description */
usageError(const char *progName, const char *msg)
{
    if (msg != NULL)
        fprintf(stderr, "%s", msg);
    fprintf(stderr, "Usage: %s [-n] msqid msg-type [msg-text]\n", progName);
    fprintf(stderr, "    -n       Use IPC_NOWAIT flag\n");
    exit(EXIT_FAILURE);
}

int
main(int argc, char *argv[])
{
    int msqid, flags, msgLen;
    struct mbuf msg;                    /* Message buffer for msgsnd() */
    int opt;                            /* Option character from getopt() */

    /* Parse command-line options and arguments */

    flags = 0;
    while ((opt = getopt(argc, argv, "n")) != -1) {
        if (opt == 'n')
            flags |= IPC_NOWAIT;
        else
            usageError(argv[0], NULL);
    }

    if (argc < optind + 2 || argc > optind + 3)
        usageError(argv[0], "Wrong number of arguments\n");

    msqid = getInt(argv[optind], 0, "msqid");
    msg.mtype = getInt(argv[optind + 1], 0, "msg-type");

    if (argc > optind + 2) {            /* 'msg-text' was supplied */
        msgLen = strlen(argv[optind + 2]) + 1;
        if (msgLen > MAX_MTEXT)
            cmdLineErr("msg-text too long (max: %d characters)\n", MAX_MTEXT);

        memcpy(msg.mtext, argv[optind + 2], msgLen);

    } else {                            /* No 'msg-text' ==> zero-length msg */
        msgLen = 0;
    }

    /* Send message */

    if (msgsnd(msqid, &msg, msgLen, flags) == -1)
        errExit("msgsnd");

    exit(EXIT_SUCCESS);
}