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UNIX for Advanced & Expert Users
UNIX Message Queues vs. Sockets
Post 302111200 by Perderabo on Tuesday 20th of March 2007 01:42:50 AM
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#include <sys/ipc.h>
#include <sys/msg.h>
int main()
{
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struct msgbuf mesg;
qid=msgget(IPC_PRIVATE,IPC_CREAT);
mesg.mtype=1L;
mesg.mtext=1;
t=msgsnd(qid,&mesg,1,0);
printf("%d",t);
}
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LEARN ABOUT NETBSD
msgget
MSGGET(2) BSD System Calls Manual MSGGET(2) NAME
msgget -- get message queue identifier LIBRARY
Standard C Library (libc, -lc) SYNOPSIS
#include <sys/msg.h> int msgget(key_t key, int msgflg); DESCRIPTION
The msgget() system call returns the message queue identifier associated with key. A message queue identifier is a unique integer greater than zero. A message queue is created if either key is equal to IPC_PRIVATE, or key does not have a message queue identifier associated with it and the IPC_CREAT bit is set in msgflg. If both the IPC_CREAT bit and the IPC_EXCL bit are set in msgflg, and key has a message queue identifier associated with it already, the operation will fail. If a new message queue is created, the data structure associated with it (the msqid_ds structure, see msgctl(2)) is initialized as follows: o msg_perm.cuid and msg_perm.uid are set to the effective uid of the calling process. o msg_perm.gid and msg_perm.cgid are set to the effective gid of the calling process. o msg_perm.mode is set to the lower 9 bits of msgflg. o msg_qnum, msg_lspid, msg_lrpid, msg_rtime, and msg_stime are set to 0. o msg_qbytes is set to the system wide maximum value for the number of bytes in a queue (MSGMNB). o msg_ctime is set to the current time. RETURN VALUES
Upon successful completion a positive message queue identifier is returned. Otherwise, -1 is returned and the global variable errno is set to indicate the error. ERRORS
[EACCES] A message queue is already associated with key and the caller has no permission to access it. [EEXIST] Both IPC_CREAT and IPC_EXCL are set in msgflg, and a message queue is already associated with key. [ENOSPC] A new message queue could not be created because the system limit for the number of message queues has been reached. [ENOENT] IPC_CREAT is not set in msgflg and no message queue associated with key was found. SEE ALSO
msgctl(2), msgrcv(2), msgsnd(2), ftok(3) STANDARDS
The msgget system call conforms to X/Open System Interfaces and Headers Issue 5 (``XSH5''). HISTORY
Message queues appeared in the first release of AT&T System V UNIX. BSD
May 13, 2004 BSD