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msgrcv(2)				   System Calls 				msgrcv(2)

       msgrcv - message receive operation

       #include <sys/msg.h>

       ssize_t msgrcv(int msqid, void *msgp, size_t msgsz,
	    long int msgtyp, int msgflg);

       The  msgrcv()  function	reads  a message from the queue associated with the message queue
       identifier specified by msqid and places it in the user-defined buffer pointed to by msgp.

       The msgp argument points to a user-defined buffer that must contain first a field of  type
       long int that will specify the type of the message, and then a data portion that will hold
       the data bytes of the message. The structure below is an example of what this user-defined
       buffer might look like:

	 struct mymsg {
		 long int    mtype;	/* message type */
		 char	     mtext[1];	/* message text */

       The mtype member is the received message's type as specified by the sending process.

       The mtext member is the text of the message.

       The   msgsz  argument  specifies the size in bytes of mtext. The received message is trun-
       cated to msgsz bytes if it is larger than msgsz and (msgflg&MSG_NOERROR) is non-zero.  The
       truncated  part of the message is lost and no indication of the truncation is given to the
       calling process.

       The msgtyp argument specifies the type of message requested as follows:

	   o	  If msgtyp is 0, the first message on the queue is received.

	   o	  If msgtyp is greater than 0, the first message of type msgtyp is received.

	   o	  If msgtyp is less than 0, the first message of the lowest  type  that  is  less
		  than or equal to the absolute value of msgtyp is received.

       The  msgflg  argument specifies which of the following actions is to be taken if a message
       of the desired type is not on the queue:

	   o	  If (msgflg&IPC_NOWAIT) is non-zero, the calling process will return immediately
		  with a return value of -1 and errno set to ENOMSG.

	   o	  If  (msgflg&IPC_NOWAIT)  is 0, the calling process will suspend execution until
		  one of the following occurs:

	       o      A message of the desired type is placed on the queue.

	       o      The message  queue  identifier  msqid  is  removed  from	the  system  (see
		      msgctl(2));  when  this  occurs,	errno  is  set	equal  to EIDRM and -1 is

	       o      The calling process receives a signal that is to be caught; in this case	a
		      message  is  not	received and the calling process resumes execution in the
		      manner prescribed in sigaction(2).

       Upon successful completion, the following actions are  taken  with  respect  to	the  data
       structure associated with msqid (see Intro(2)):

	   o	  msg_qnum is decremented by 1.

	   o	  msg_lrpid is set equal to the process ID of the calling process.

	   o	  msg_rtime is set equal to the current time.

       Upon successful completion, msgrcv() returns a value equal to the number of bytes actually
       placed into the buffer mtext. Otherwise, -1 is returned, no message is received, and errno
       is set to indicate the error.

       The msgrcv() function will fail if:

       E2BIG	 The value of mtext is greater than msgsz and (msgflg&MSG_NOERROR) is 0.

       EACCES	 Operation permission is denied to the calling process.  See Intro(2).

       EIDRM	 The message queue identifier msqid is removed from the system.

       EINTR	 The msgrcv() function was interrupted by a signal.

       EINVAL	 The msqid argument is not a valid message queue identifier.

       ENOMSG	 The queue does not contain a message of the desired type and (msgflg&IPC_NOWAIT)
		 is non-zero.

       The msgrcv() function may fail if:

	EFAULT	  The msgp argument points to an illegal address.

       The value passed as the msgp argument should be converted to type void *.

       See attributes(5) for descriptions of the following attributes:

       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       |Interface Stability	     |Standard			   |

       Intro(2), msgctl(2), msgget(2), msgsnd(2), sigaction(2), attributes(5), standards(5)

SunOS 5.11				   19 May 1999					msgrcv(2)
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