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);
 }