SHMAT(2) BSD System Calls Manual SHMAT(2)NAME
shmat, shmdt — attach or detach shared memory
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <machine/param.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
void *
shmat(int shmid, void *addr, int flag);
int
shmdt(void *addr);
DESCRIPTIONShmat() attaches the shared memory segment identified by shmid to the
calling process's address space. The address where the segment is
attached is determined as follows:
· If addr is 0, the segment is attached at an address selected by the
kernel.
· If addr is nonzero and SHM_RND is not specified in flag, the segment
is attached the specified address.
· If addr is specified and SHM_RND is specified, addr is rounded down
to the nearest multiple of SHMLBA.
Shmdt() detaches the shared memory segment at the address specified by
addr from the calling process's address space.
RETURN VALUES
Upon success, shmat() returns the address where the segment is attached;
otherwise, -1 is returned and errno is set to indicate the error.
The shmdt() function returns the value 0 if successful; otherwise the
value -1 is returned and the global variable errno is set to indicate the
error.
ERRORSShmat() will fail if:
[EINVAL] No shared memory segment was found corresponding to
shmid.
[EINVAL] addr was not an acceptable address.
Shmdt() will fail if:
[EINVAL] addr does not point to a shared memory segment.
SEE ALSOshmctl(2), shmget(2)BSD August 2, 1995 BSD
