Name

Library

Synopsis

Return values

The shmdt function returns the value 0 if successful; otherwise the value -1 is returned and errno is set to indicate the error.

Detailed description

• 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. (a nonzero addr is not supported)
• If addr is specified and SHM_RND is specified, addr is rounded down to the nearest multiple of SHMLBA.(a nonzero addr is not supported)

The shmdt system call detaches the shared memory segment at the address specified by addr from the calling process’s address space.

Examples

#include <sys/ipc.h>
#include <sys/shm.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>

         
#define SHM_SEG_SIZE 1024

         
int main(void)
{
    int shm_id;
    char *shm_addr;
    /*
     * Create a shared memory segment
     */
    if ((shm_id = shmget(IPC_PRIVATE, SHM_SEG_SIZE,
                         IPC_CREAT | IPC_EXCL | 0666))
         == -1) {
        printf("Shared memory create failed with errno %d\n", errno);
        return -1;
    }
    /*
     * Attach the shared memory segment to the
     * process address space
     */
    if((shm_addr = (char *)shmat(shm_id, NULL, 0)) == (void *)-1) {
       printf("Shared memory attach failed with errno %d\n", errno);
       return -1;
    }
    /*
     * Copy data to shared memory segment
     */
    strcpy(shm_addr, "some_random_data");
    /*
     * Detach the shared memory segment
     */
    if(shmdt(shm_addr) == -1) {
       printf("Shared memory detach failed with errno %d\n", errno);
    }
    /*
     * Remove the shared memory segment
     */
    if(shmctl(shm_id, IPC_RMID, NULL) == -1) {
       printf("Shared memory destroy failed with errno %d\n", errno);
    }
    return 0;
}

         

Errors

The shmdt system call will fail if:

See also

Feedback