Accessing a Shared Memory Segment

shmget(2) is used to obtain access to a shared memory segment. When the call succeeds, it returns the shared memory segment ID (shmid). The following code illustrates shmget(2).

#include                     <sys/types.h>
#include                     <sys/ipc.h>
#include                     <sys/shm.h>
...
        key_t     key;       /* key to be passed to shmget() */
        int       shmflg;    /* shmflg to be passed to shmget() */
        int       shmid;     /* return value from shmget() */
        size_t    size;      /* size to be passed to shmget() */
        ...
        key = ...
        size = ...
        shmflg) = ...
        if ((shmid = shmget (key, size, shmflg)) == –1) {
               perror("shmget: shmget failed");
               exit(1);
        } else {
               (void) fprintf(stderr,
                             "shmget: shmget returned %d\n", shmid);
               exit(0);
        }
...