|MSGRCV(2)||System Calls Manual||MSGRCV(2)|
msgrcv — receive a
message from a message queue
msqid, void *msgp,
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
long mtype; /* message type */ char mtext; /* 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
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
depends on whether the
IPC_NOWAIT flag is set in
msgflg or not. If
msgrcv() will immediately return a value of
-1, and set errno to
IPC_NOWAIT is not set, the calling process will
be blocked until:
If a message is successfully received, the data structure associated with msqid is updated as follows:
Upon successful completion,
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
msgrcv() will fail if:
msgsz is less than 0.
MSG_NOERRORflag was not set in msgflg.
IPC_NOWAITis set in msgflg.
msgrcv() was waiting for a message of the requested type to become available on it.
msgrcv() function conforms to the
X/Open System Interfaces option of IEEE Std 1003.1-2008
Message queues first appeared in AT&T System V Release 1 UNIX and have been available since NetBSD 1.0.
|July 18, 2019||OpenBSD-current|