Dear Friends, Any idea why the msgrcv is receiving a blank buffer?
Here is the code:
enter code here
#include <sys/msg.h>
#include <unistd.h>
#include <sys/types.h>
#include <stdio.h>
#include <string.h>
typedef struct mymsg {
long mtype;
char mtext[24];
}mymsg;
int main()
{
int msqid;
mymsg msg,buff;
msqid=msgget(IPC_PRIVATE,IPC_CREAT|IPC_EXCL);
if(msqid==-1){
perror("FAiled to create message queue\n");
}
else{
printf("Message queue id:%u\n",msqid);
}
msg.mtype=1;
strcpy(msg.mtext,"This is a message");
if(msgsnd(msqid,&msg,sizeof(msg.mtext),0)==-1){
perror("msgsnd failed:");
}
else{
printf("Message sent successfully\n");
}
//ssize_t msgrcv(int msqid, void *msgp, size_t msgsz, long msgtyp,int msgflg);
// msgrcv(msqid,buff.mtext,sizeof(msg.mtext),1,0); This was error
msgrcv(msqid,&buff,sizeof(msg.mtext),1,0); // This is correct (Thanks to Erik)
printf("The message received is: %s\n",buff.mtext);
}
Output:
[root@dhcppc0 message_queue]# ./a.out
Message queue id:294919
Message sent successfully
The message received is:
1,1 Top
msgbuf.mtype
must be set to 1 - since you're telling msgrcv
that you want messages of type 1.
Alternatively, you could set msgbuf.mtype
to any positive value, and then tell msgrcv
that you want any message type by passing 0 as the msgtyp
argument.
Also, msgrcv
expects a pointer to a msgbuf
:
msgrcv(msqid,&buff,sizeof(msg.mtext),1,0);
EDIT: Tested working source:
#include <sys/msg.h>
#include <unistd.h>
#include <sys/types.h>
#include <stdio.h>
#include <string.h>
typedef struct mymsg {
long mtype;
char mtext[24];
}mymsg;
int main()
{
int msqid;
mymsg msg,buff;
msqid=msgget(IPC_PRIVATE,IPC_CREAT|IPC_EXCL);
if(msqid==-1){
perror("FAiled to create message queue\n");
}
else{
printf("Message queue id:%u\n",msqid);
}
msg.mtype=1; // was there failed to copy
strcpy(msg.mtext,"This is a message");
if(msgsnd(msqid,&msg,sizeof(msg.mtext),0)==-1){
perror("msgsnd failed:");
}
else{
printf("Message sent successfully\n");
}
//ssize_t msgrcv(int msqid, void *msgp, size_t msgsz, long msgtyp,int msgflg);
msgrcv(msqid,&buff,sizeof(msg.mtext),1,0);
printf("The message received is: %s\n",buff.mtext);
}