共享内存

// shmCreateAndWrite.c
#include <stdio.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <sys/stat.h>
int main ()
{
int segment_id;
char bogus;
char* shared_memory;
struct shmid_ds shmbuffer;
int segment_size;
const int shared_segment_size = 0x6400;
/* Allocate a shared memory segment. */
segment_id = shmget (IPC_PRIVATE, shared_segment_size, IPC_CREAT | IPC_EXCL | S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP);
/* Attach the shared memory segment. */
printf("Shared memory segment ID is %d\n", segment_id);
shared_memory = (char*) shmat (segment_id, 0, 0);
printf ("shared memory attached at address %p\n", shared_memory);
/* Determine the segment's size. */
/*
shmctl (segment_id, IPC_STAT, &shmbuffer);
segment_size = shmbuffer.shm_segsz;
printf ("segment size: %d\n", segment_size);
*/
/* Write a string to the shared memory segment. */
sprintf (shared_memory, "Hello, world.");
/* Detach the shared memory segment. */
shmdt (shared_memory);
printf("Wrote Hello World to the segment\n");
}
// shmDeleteExisting.c
#include <stdio.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <sys/stat.h>
int main ()
{
int segment_id;
printf("Enter the shared memory id: ");
scanf("%d", &segment_id);
/* Deallocate the segment. */
shmctl (segment_id, IPC_RMID, 0);
return 0;
}
// shmReadExisting.c
#include <stdio.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <sys/stat.h>
int main ()
{
int segment_id;
char bogus;
char* shared_memory;
struct shmid_ds shmbuffer;
int segment_size;
const int shared_segment_size = 0x6400;
printf("Enter the shared memory id: ");
scanf("%d", &segment_id);
/* Reattach the shared memory segment, at a different address. */
shared_memory = (char*) shmat (segment_id, (void*) 0x5000000, 0);
printf ("shared memory reattached at address %p\n", shared_memory);
/* Print out the string from shared memory. */
printf ("The contents of the shared memory is:\n%s\n", shared_memory);
/* Detach the shared memory segment. */
shmdt (shared_memory);
return 0;
}
// shmWriteExisting.c
#include <stdio.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <sys/stat.h>
#include <time.h>
int main ()
{
int segment_id;
char bogus;
char* shared_memory;
struct shmid_ds shmbuffer;
int segment_size;
const int shared_segment_size = 0x6400;
time_t t;
time(&t);
printf("Enter the shared memory id: ");
scanf("%d", &segment_id);
/* Reattach the shared memory segment, at a different address. */
shared_memory = (char*) shmat (segment_id, (void*) 0x5000000, 0);
printf ("shared memory reattached at address %p\n", shared_memory);
/* Add to the segment */
sprintf (shared_memory, "Modified the segment at %s", ctime(&t));
/* Print out the string from shared memory. */
printf ("The contents of the shared memory is:\n%s", shared_memory);
printf ("#################################################\n");
return 0;
}