Message Queue Problem

[oxpac]

send.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

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

int main( int argc, char **argv)
{
struct msgbuf buf;
int mid;
key_t key = 0x10;
int ch;
mid = msgget(key,IPC_CREAT|0666);

if(-1 == mid ){
perror("msgget");
exit(0);
}
while ( 1 )
{
printf("Enter Msg:");
fgets(buf.mbuf,sizeof buf.mbuf,stdin);

if(!strcmp(buf.mbuf,"q\n")) {
if (-1 == msgsnd(mid,&buf,sizeof buf,0))
{
perror("msgsnd");
}
exit(0);
}
printf("Enter type:");
scanf("%d",&buf.type);
getchar();
if (-1 == msgsnd(mid,&buf,sizeof buf,0))
{
perror("msgsnd");
exit(0);
}
}
return 0;
}


rece.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

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

int main( int argc, char **argv)
{
struct msgbuf buf;
int mid;
key_t key = 0x10;

mid = msgget(key,IPC_CREAT|0666);

if(-1 == mid ){
perror("msgget");
exit(0);
}
while ( 1 )
{
//printf("Enter type to read:");
//scanf("%d",&buf.type);

if ( msgrcv(mid,&buf,sizeof buf,0,0) == -1)
{
perror("msgrcv");
exit(0);
}

if(!strcmp(buf.mbuf,"q\n"))
exit(0);
printf("type : %d \n", buf.type);
printf("Msg : %s \n",buf.mbuf);
}
return 0;
}


msgq_heads.h

#define SIZE 50
struct msgbuf {
int type;
char mbuf[SIZE];
};



Below are the two programs i am using to send and receive messages from the one process to other.
The receive program is working fine with the statement "msgrcv(mid,&buf,sizeof buf,0,0)".
That means it is reading all the messages available in the queue.

But when i use the statement "msgrcv(mid,&buf,sizeof buf,buf.type,0)" by reading the type from the code that
is commented it seems it is waiting or blocking.

I dont understand what i am doing wrong, please correct me.

[oxpac]

I understood the problem, it is silly though.
The datatype what i have choosen for type in msgbuf is

"int"

but the msgrcv functions type parameter is

"long"

.

I changed the type to long it is working fine.

But i wonder the representation of 1 in int and long is supposed to be same ,
except the other extra bytes in long in case sizeof (long) > sizeof (int) which are any way zeros.

Infact i have written a program to check the sizes of int and long and the compiler reported
int is of 4 and long is of 8 bytes and i == l in below program.

But why was above the program not working when used int instead of long.

#include <stdio.h>
int main( void )
{
    struct INT{
        int i;
    }I;
    I.i =1;

    struct LONG{
    long l;
    }L;
    L.l = 1;

    printf("sizeof int  = %ld" , sizeof (int));
    printf("\nsizeof long  = %ld", sizeof (long));

    if (I.i == L.l){
        printf("\ni == l");
    }else{
        printf("\ni != l");
    }
    return 0;
}