Message queue error (invalid arguement) with Qt

[Dcqt]

Hi,

The question is not actually related to Qt problem, it is more general of *nix IPC.

I am trying to use message queues with Qt , below is the code.

the function
@ msgsnd(msgid,&msg_struct[0],sizeof(msg_struct[0]),0); @ is failing with msg

msgsnd (create_sender): Invalid argument

instead of &msg_struct[ 0 ] if i use msg_struct[ 0 ].msg_buff it is working .
i do not understand the problem. as the arguement is void * for msgsnd it should work in both the cases.

sender.pro

sender.cpp
@

#include "sender.h"
#include<QDebug>
#include <sys/ipc.h>
#include <sys/types.h>
#include<sys/msg.h>

Sender::Sender(QWidget *parent)
: QMainWindow(parent)
{
create_sender("msg1",8);
}

Sender::~Sender()
{

}
int Sender :: create_sender(char *appname,int pos)
{
int msgid;
int res;

struct st_msg_buff{
     char msg_buff[50];
     int msg_type;
     int pos;
 };

struct st_msg_buff msg_struct[1];

msgid = msgget(0x7890,IPC_CREAT|0777);

qDebug()<<"msgid (create_sender)" << msgid;

if(-1 == msgid ){
    perror("msgget (create_sender)");
    return 0;
}

strcpy(msg_struct[0].msg_buff,appname);
msg_struct[0].msg_buff[strlen(appname)]=0;
msg_struct[0].msg_type = 0;
msg_struct[0].pos = pos;

qDebug() <<"pos in Sender" <<msg_struct[0].pos;
res = msgsnd(msgid,&msg_struct[0],sizeof(msg_struct[0]),0);

if(-1 == res ){
    perror("msgsnd (create_sender)");
    return 0;
}else
{
    qDebug() <<"msg sent (create_sender) successfully";
}
 return 0;

}

@

main.cpp
@
#include "sender.h"
#include <QApplication>

int main(int argc, char *argv[])
{
QApplication a(argc, argv);
Sender w;
w.show();

return a.exec();

}
@

sender.h
@
#ifndef SENDER_H
#define SENDER_H

#include <QMainWindow>

class Sender : public QMainWindow
{
Q_OBJECT

public:
Sender(QWidget *parent = 0);
~Sender();
int create_sender(char *appname,int pos);
};

#endif // SENDER_H
@

receiver.pro

receiver.cpp
@
#include "receiver.h"
#include <sys/ipc.h>
#include <sys/types.h>
#include<sys/msg.h>
#include "receiver.h"
#include<QDebug>

Receiver::Receiver(QWidget *parent)
: QMainWindow(parent)
{
create_receiver();
}

void * wait_for_mesg(void *);

int Receiver :: create_receiver()
{
pthread_t tid;
if (-1 == pthread_create(&tid,NULL,wait_for_mesg,NULL) ){
perror("pthread_create");
return -1;
} else {
qDebug()<<"wait_for_mesg created suceesfully";

}

}

void * wait_for_mesg(void *arg)
{
int msgid;
int res;

struct st_msg_buff{
     char msg_buff[50];
     int msg_type;
     int pos;
 };

struct st_msg_buff msg_struct[1];

msgid = msgget(0x7890,IPC_CREAT|0777);
qDebug()<<" getting msgId in wait_for_mesg" << msgid;

if(-1 == msgid ){
    perror("Failed");
    return NULL;
} else {
    qDebug()<<"Success";
}

msg_struct[0].msg_type = 0;

res = msgrcv(msgid,msg_struct,sizeof(msg_struct[0]),0,0);
//sleep(1);

if( -1 == res ){
    perror("msgrcv: ");
    return NULL;
} else   {

    qDebug() <<"app recieved from Sender:" <<msg_struct[0].msg_buff;
    qDebug() << "pos :" << msg_struct[0].pos;

    if(msgctl(msgid,IPC_RMID,NULL) < 0)
        perror("Unable to remove msgid");
    else
      qDebug()<<"Message Queue Deleted ";
}

}
Receiver::~Receiver()
{

}

@

main.cpp
@
#include "receiver.h"
#include <QApplication>

int main(int argc, char *argv[])
{
QApplication a(argc, argv);
Receiver w;
w.show();

return a.exec();

}

@

receiver.h
@
#ifndef RECEIVER_H
#define RECEIVER_H

#include <QMainWindow>

class Receiver : public QMainWindow
{
Q_OBJECT

public:
Receiver(QWidget *parent = 0);
~Receiver();
int create_receiver();
};

#endif // RECEIVER_H

@

[SGaist]

Hi,

with msgsnd(create_sender) you are trying to call msgsnd with a function as a parameter. Is that really what you want ?

[Dcqt]

Hi,

i think you are referring to comment , that not actual code.
i have gone through other sites and i feel it is something to do with MSGSIZE in the message queue.