void
*
shmat(
int shmid
, const void *shmaddr
, int shmflg
)
int
shmdt(
const void *shmaddr
)
)
maps the shared memory segment associated with the shared memory identifier
shmid
into the address space of the calling process.
The address at which the segment is mapped is determined by the
shmaddr
parameter.
If it is equal to 0, the system will pick an address itself.
Otherwise, an attempt is made to map the shared memory segment at the
address
shmaddr
specifies.
If
SHM_RND
is set in
shmflg
,
the system will round the address down to a multiple of
SHMLBA
bytes
(
SHMLBA
is defined in
<
sys/shm.h
>).
A shared memory segment can be mapped read-only by specifying the
SHM_RDONLY
flag in
shmflg
.
shmdt()
unmaps the shared memory segment that is currently mapped at
shmaddr
from the calling process' address space.
shmaddr
must be a value returned by a prior
shmat()
call.
A shared memory segment will remain in existence until it is
removed by a call to
shmctl(2)
with the
IPC_RMID
command.
)
returns the address at which the shared memory segment has been mapped into
the calling process' address space when successful,
shmdt(
)
returns 0 on successful completion.
Otherwise, a value of -1 is returned, and the global variable
errno
is set to indicate the error.
)
will fail if:
EACCES
]
ENOMEM
]
EINVAL
]
shmid
is not a valid shared memory identifier.
shmaddr
specifies an illegal address.
EMFILE
]
shmdt()
will fail if:
EINVAL
]
shmaddr
is not the start address of a mapped shared memory segment.
AT&T
System V UNIX
.