MSGRCV(2) | System Calls Manual | MSGRCV(2) |
msgrcv
— receive a
message from a message queue
#include
<sys/msg.h>
int
msgrcv
(int
msqid, void *msgp,
size_t msgsz,
long msgtyp,
int msgflg);
The
msgrcv
()
function receives a message from the message queue specified in
msqid, and places it into the structure pointed to by
msgp. This structure should consist of the following
members:
long mtype; /* message type */ char mtext[1]; /* body of message */
mtype is an integer greater than 0 that can
be used for selecting messages, mtext is an array of
bytes, with a size up to that of the system limit
(MSGMAX
).
The value of msgtyp has one of the following meanings:
msgsz specifies the maximum length of the
requested message. If the received message has a length greater than
msgsz it will be silently truncated if the
MSG_NOERROR
flag is set in
msgflg, otherwise an error will be returned.
If no matching message is present on the message
queue specified by msqid, the behavior of
msgrcv
()
depends on whether the IPC_NOWAIT
flag is set in
msgflg or not. If IPC_NOWAIT
is set, msgrcv
() will immediately return a value of
-1, and set errno to EAGAIN
.
If IPC_NOWAIT
is not set, the calling process will
be blocked until:
EINVAL
.EINTR
.If a message is successfully received, the data structure associated with msqid is updated as follows:
Upon successful completion, msgrcv
()
returns the number of bytes received into the mtext
field of the structure pointed to by msgp. Otherwise,
-1 is returned, and errno set to indicate the
error.
msgrcv
() will fail if:
EINVAL
]msgsz is less than 0.
E2BIG
]MSG_NOERROR
flag was not set in msgflg.EACCES
]EFAULT
]EINTR
]ENOMSG
]IPC_NOWAIT
is set in
msgflg.EIDRM
]msgrcv
() was
waiting for a message of the requested type to become available on
it.Message queues appeared in AT&T System V Release 1 UNIX.
November 15, 2014 | OpenBSD-5.9 |