Linux IPC mechanism: Message Queuing example

Program msg1.c to receive messages

<span style= "FONT-SIZE:12PX;" > #include <stdio.h> #include <unistd.h> #include <string.h> #include <errno.h> #include <    Stdlib.h> #include <sys/msg.h>struct my_msg_st {long int my_msg_type; Char some_text[bufsiz];};    int main () {int running = 1;    int msgid;    struct My_msg_st some_data;    long int msg_to_receive = 0; Establish Message Queuing MsgId = Msgget ((key_t) 1234, 0666 |    Ipc_creat);        if (-1 = = MsgId) {fprintf (stderr, "Msgget failed with error:%d\n", errno);    Exit (Exit_failure);        }//Get the message from the message queue until you meet end while (running) {memset (Some_data.some_text, ' n ', bufsiz); if (-1 = = MSGRCV (MsgId, (void *) &some_data, Bufsiz, msg_to_receive, 0)) {fprintf (stderr, "MAGRCV faile            D with Error%d\n ", errno);        Exit (Exit_failure);        } printf ("You wrote:%s", some_data.some_text); Some_data.some_text[strlen (Some_data.some_text)-1] = ' + ';  Remove line break to find end flag string exactly      if (0 = = strcmp (Some_data.some_text, "End")) running = 0;            }//Delete Message Queuing if (-1 = = Msgctl (msgid, Ipc_rmid, 0)) {fprintf (stderr, "Msgctl (ipc_rmid) failed\n");    Exit (Exit_failure); } exit (exit_success);} </span>

Program msg2.c for sending messages:

<span style= "FONT-SIZE:12PX;" > #include <stdlib.h> #include <stdio.h> #include <unistd.h> #include <string.h> #include    <errno.h> #include <sys/msg.h> #define Max_text 512struct my_msg_st {long int my_msg_type; Char some_text[max_text];};    int main () {int running = 1;    struct My_msg_st some_data;    int msgid;    Char Buffer[bufsiz]; MsgId = Msgget ((key_t) 1234, 0666 |    Ipc_creat);        if (-1 = = MsgId) {fprintf (stderr, "Msgget failed with error%d\n", errno);    Exit (Exit_failure);        }//Send message while (running) {memset (buffer, ' + ', bufsiz);        printf ("Enter some text:");        Fgets (buffer, bufsiz, stdin);        Some_data.my_msg_type = 1;        strcpy (some_data.some_text, buffer); if (-1 = = Msgsnd (MsgId, (void *) &some_data, Max_text, 0)) {fprintf (stderr, "msgsnd failed with error%            D\n ", errno);        Exit (Exit_failure); } buffer[strlen (buffer)-1] = ' N ';    if (0 = = strcmp (buffer, "end")) running = 0; } exit (exit_success);} </span>

Output Result:

[Email protected] document]$./MSG2
Enter some Text:hey man
Enter some text:how is you
Enter some text:endsss
Enter some Text:end
[Email protected] document]$./MSG1
You Wrote:hey Mans
You wrote:how is
You wrote:endsss
You wrote:end

The advantage of Message Queuing over named Pipes is that it exists independently of the send and receive processes, eliminating some of the difficulties that can arise when synchronizing named Pipes for opening and closing.

Linux IPC mechanism: Message Queuing example