08-25-2008
message queues
#include <sys/ipc.h>
#include <sys/msg.h>
int main()
{
int qid;
int t;
struct msgbuf mesg;
qid=msgget(IPC_PRIVATE,IPC_CREAT);
mesg.mtype=1L;
mesg.mtext[0]=1;
t=msgsnd(qid,&mesg,1,0);
printf("%d",t);
}
the program prints -1 as the result of msgsnd ,which means that msgsnd doesn't work...any ideas??
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MESG(1) BSD General Commands Manual MESG(1)
NAME
mesg -- display (do not display) messages from other users
SYNOPSIS
mesg [n | y]
DESCRIPTION
The mesg utility is invoked by a user to control write access others have to a terminal device. Write access is allowed by default, and pro-
grams such as talk(1) and write(1) may display messages on the terminal.
The first terminal device in the sequence of devices associated with standard input, standard output and standard error is affected.
The following options are available:
n Disallow messages.
y Permit messages to be displayed.
If no arguments are given, mesg displays the present message status to the standard output.
EXIT STATUS
The mesg utility exits with one of the following values:
0 Messages are allowed.
1 Messages are not allowed.
>1 An error has occurred.
EXAMPLES
Disallow messages from other users to the current terminal:
mesg n
Allow messages from other users to ttyp1 (assuming you are also logged in on that terminal):
mesg y </dev/ttyp1
COMPATIBILITY
Previous versions of the mesg utility wrote the message status to the standard error output and affected the terminal attached to standard
error without first trying the standard input or output devices.
SEE ALSO
biff(1), talk(1), wall(1), write(1)
STANDARDS
The mesg utility conforms to IEEE Std 1003.1-2001 (``POSIX.1'').
HISTORY
A mesg command appeared in Version 1 AT&T UNIX.
BSD
May 5, 2002 BSD