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msgrcv (3)
  • msgrcv (2) ( Solaris man: Системные вызовы )
  • msgrcv (2) ( Русские man: Системные вызовы )
  • msgrcv (2) ( Linux man: Системные вызовы )
  • >> msgrcv (3) ( FreeBSD man: Библиотечные вызовы )
  • msgrcv (3) ( POSIX man: Библиотечные вызовы )

  • BSD mandoc
     

    NAME

    
    
    msgrcv
    
     - receive a message from a message queue
    
     
    

    LIBRARY

    Lb libc
    
     
    

    SYNOPSIS

       #include <sys/types.h>
       #include <sys/ipc.h>
       #include <sys/msg.h>
    int msgrcv (int msqid void *msgp size_t msgsz long msgtyp int msgflg);
     

    DESCRIPTION

    The msgrcv ();
    function receives a message from the message queue specified in Fa msqid , and places it into the structure pointed to by Fa 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 Fa msgtyp has one of the following meanings:

    The Fa msgsz argument specifies the maximum length of the requested message. If the received message has a length greater than Fa msgsz it will be silently truncated if the MSG_NOERROR flag is set in Fa msgflg , otherwise an error will be returned.

    If no matching message is present on the message queue specified by Fa msqid , the behavior of msgrcv ();
    depends on whether the IPC_NOWAIT flag is set in Fa msgflg or not. If IPC_NOWAIT is set, msgrcv ();
    will immediately return a value of -1, and set errno to Er ENOMSG . If IPC_NOWAIT is not set, the calling process will be blocked until:

    If a message is successfully received, the data structure associated with Fa msqid is updated as follows:

     

    RETURN VALUES

    Upon successful completion, msgrcv ();
    returns the number of bytes received into the mtext field of the structure pointed to by Fa msgp . Otherwise, -1 is returned, and errno set to indicate the error.  

    ERRORS

    The msgrcv ();
    function will fail if:

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

    The message queue was removed while msgrcv ();
    was waiting for a message of the requested type to become available on it.

    The Fa msgsz argument is less than 0.

    Bq Er E2BIG
    A matching message was received, but its size was greater than Fa msgsz and the MSG_NOERROR flag was not set in Fa msgflg .
    Bq Er EACCES
    The calling process does not have read access to the message queue.
    Bq Er EFAULT
    The Fa msgp argument points to an invalid address.
    Bq Er EINTR
    The system call was interrupted by the delivery of a signal.
    Bq Er ENOMSG
    There is no message of the requested type available on the message queue, and IPC_NOWAIT is set in Fa msgflg .

     

    SEE ALSO

    msgctl(3), msgget(3), msgsnd(3)  

    HISTORY

    Message queues appeared in the first release of AT&T System V .


     

    Index

    NAME
    LIBRARY
    SYNOPSIS
    DESCRIPTION
    RETURN VALUES
    ERRORS
    SEE ALSO
    HISTORY


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