msgget(2)
NAME
msgget − get message queue
SYNTAX
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>
int msgget(key, msgflg)
key_t key;
int msgflg;
DESCRIPTION
The msgget system call returns the message queue identifier associated with key.
A message queue identifier and associated message queue and data structure (see intro(2)) are created for key if one of the following are true:
•The key is IPC_PRIVATE.
•The key does not already have a message queue identifier associated with it, and ( msgflg & IPC_CREAT) is true.
Upon creation, the data structure associated with the new message queue identifier is initialized as follows:
•The msg_perm.cuid, msg_perm.uid, msg_perm.cgid, and msg_perm.gid are set equal to the effective user ID and effective group ID, respectively, of the calling process.
•The low-order 9 bits of msg_perm.mode are set equal to the low-order 9 bits of msgflg.
•The msg_qnum, msg_lspid, msg_lrpid, msg_stime, and msg_rtime are set equal to 0.
•The msg_ctime is set equal to the current time.
•The msg_qbytes is set equal to the system limit.
RETURN VALUE
If successful, returns the message queue identifier. If unsuccessful, returns a −1, and the global variable errno indicates the error code.
DIAGNOSTICS
The msgget call will fail if:
[EACCES] A message queue identifier exists for key, but operation permission as specified by the low-order 9 bits of msgflg would not be granted. For further information, see intro(2).
[ENOENT] A message queue identifier does not exist for key, and ( msgflg & IPC_CREAT ) is false.
[ENOSPC] A message queue identifier is to be created, but the system-imposed limit on the maximum number of allowed message queue identifiers system wide would be exceeded.
[EEXIST] A message queue identifier exists for key, but ( ( msgflg & IPC_CREAT ) & ( msgflg & IPC_EXCL ) ) is true.