SHMOP(2)             INTERACTIVE UNIX System             SHMOP(2)



          NAME
               shmop: shmat, shmdt - shared memory operations

          SYNOPSIS
               #include <sys/types.h>
               #include <sys/ipc.h>
               #include <sys/shm.h>

               char *shmat (shmid, shmaddr, shmflg)
               int shmid;
               char *shmaddr;
               int shmflg;

               int shmdt (shmaddr)
               char *shmaddr;

          DESCRIPTION
               The shmat system call attaches the shared memory segment
               associated with the shared memory identifier specified by
               shmid to the data segment of the calling process.  The seg-
               ment is attached at the address specified by one of the fol-
               lowing criteria:

                    If shmaddr is equal to zero, the segment is attached at
                    the first available address as selected by the system.

                    If shmaddr is not equal to zero and (shmflg & SHM_RND)
                    is ``true'', the segment is attached at the address
                    given by (shmaddr - (shmaddr modulus SHMLBA)).

                    If shmaddr is not equal to zero and (shmflg & SHM_RND)
                    is ``false'', the segment is attached at the address
                    given by shmaddr.

               Shmdt detaches from the calling process's data segment the
               shared memory segment located at the address specified by
               shmaddr.

               The segment is attached for reading if (shmflg & SHM_RDONLY)
               is ``true'' {READ}; otherwise it is attached for reading and
               writing {READ/WRITE}.

               Shmat will fail and not attach the shared memory segment if
               one or more of the following is true:

               [EINVAL]       Shmid is not a valid shared memory identif-
                              ier.

               [EACCES]       Operation permission is denied to the calling
                              process [see intro(2)].

               [ENOMEM]       The available data space is not large enough
                              to accommodate the shared memory segment.


          Rev. C Software Development Set                            Page 1

          SHMOP(2)             INTERACTIVE UNIX System             SHMOP(2)



               [EINVAL]       Shmaddr is not equal to zero, and the value
                              of (shmaddr - (shmaddr modulus SHMLBA)) is an
                              illegal address.

               [EINVAL]       Shmaddr is not equal to zero, (shmflg &
                              SHM_RND) is ``false'', and the value of
                              shmaddr is an illegal address.

               [EMFILE]       The number of shared memory segments attached
                              to the calling process would exceed the
                              system-imposed limit.

               [EINVAL]       Shmdt will fail and not detach the shared
                              memory segment if shmaddr is not the data
                              segment start address of a shared memory seg-
                              ment.

          SEE ALSO
               exec(2), exit(2), fork(2), intro(2), shmctl(2), shmget(2).

          DIAGNOSTICS
               Upon successful completion, the return value is as follows:

                    Shmat returns the data segment start address of the
                    attached shared memory segment.

                    Shmdt returns a value of 0.

               Otherwise, a value of -1 is returned, and errno is set to
               indicate the error.

          NOTES
               The user must explicitly remove shared memory segments after
               the last reference to them has been removed.





















          Rev. C Software Development Set                            Page 2