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msgget — get message queue
Standard C Library (libc, -lc)
#include <sys/msg.h> int msgget(key_t key, int msgflg);
The msgget() function 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 a new message queue is created, the data structure associated with it (the msqid_ds structure, see msgctl(2)) is initialized as follows: • msg_perm.cuid and msg_perm.uid are set to the effective uid of the calling process. • msg_perm.gid and msg_perm.cgid are set to the effective gid of the calling process. • msg_perm.mode is set to the lower 9 bits of msgflg which are set by ORing these constants: 0400 Read access for user. 0200 Write access for user. 0040 Read access for group. 0020 Write access for group. 0004 Read access for other. 0002 Write access for other. • msg_cbytes, msg_qnum, msg_lspid, msg_lrpid, msg_rtime, and msg_stime are set to 0. • msg_qbytes is set to the system wide maximum value for the number of bytes in a queue (MSGMNB). • msg_ctime is set to the current time.
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.
[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 was not set in msgflg and no message queue associated with key was found.
Message queues appeared in the first release of AT&T System V UNIX.