This is an efficient way of passing a block of data between two unrelated processes. This technique is similar to named pipes, but the major difference is that we don't need to handle opening and closing the pipes. Here, the advantage of this technique over named pipes is that the message queue exists independently of both the sending and receiving processes.
Source code of message_receiver.c
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <sys/msg.h>
struct msg_st {
long int msg_type;
char text[BUFSIZ];
};
int main() {
int running = 1;
int msgid;
struct msg_st data;
long int msg_to_receive = 0;
msgid = msgget((key_t) 1234, 0666 | IPC_CREAT);
if (msgid == -1) {
fprintf(stderr, "msgget failed with error: %d\n", errno);
exit(EXIT_FAILURE);
}
while (running) {
if (msgrcv(msgid, (void *) &data, BUFSIZ, msg_to_receive, 0)
== -1) {
fprintf(stderr, "msgrcv failed with error: %d\n", errno);
exit(EXIT_FAILURE);
}
printf("You wrote: %s", data.text);
if (strncmp(data.text, "end", 3) == 0) {
running = 0;
}
}
if (msgctl(msgid, IPC_RMID, 0) == -1) {
fprintf(stderr, "msgctl(IPC_RMID) failed\n");
exit(EXIT_FAILURE);
}
exit(EXIT_SUCCESS);
}
Source code of message_sender.c
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <sys/msg.h>
#define MAX_TEXT 512
struct msg_st {
long int msg_type;
char text[MAX_TEXT];
};
int main() {
int running = 1;
struct msg_st data;
int msgid;
char buffer[BUFSIZ];
msgid = msgget((key_t) 1234, 0666 | IPC_CREAT);
if (msgid == -1) {
fprintf(stderr, "msgget failed with error: %d\n", errno);
exit(EXIT_FAILURE);
}
while (running) {
printf("Enter some text: ");
fgets(buffer, BUFSIZ, stdin);
data.msg_type = 1;
strcpy(data.text, buffer);
if (msgsnd(msgid, (void *) &data, MAX_TEXT, 0) == -1) {
fprintf(stderr, "msgsnd failed\n");
exit(EXIT_FAILURE);
}
if (strncmp(buffer, "end", 3) == 0) {
running = 0;
}
}
exit(EXIT_SUCCESS);
}
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