Shared Memory, Write Example in operating system?

Write Example
 

/* File Mapping */
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/shm.h>
#include <unistd.h>

int main() {
  int filesz = 4096; // find the length and round
                     // to multiples of 4096
  int fd, offset = 0;
  fd = shm_open("/shm1", O_CREAT | O_RDWR, 0666);
  if (fd < 0) {
    perror("open");
    exit(1);
  }
  ftruncate(fd, filesz);
  void *pbase;
  pbase = mmap(0, filesz, PROT_WRITE, MAP_SHARED, fd, offset);
  if (pbase == MAP_FAILED) {
    fprintf(stderr, "mapping failed\n");
    // close(fd);
    exit(1);
  }
  char buf[64];
  char str[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
  strncpy(pbase, str, 20); // for loop
  /*strncpy(buf,pbase,10);
      printf("buf=%s\n",buf);
      strcpy(buf,pbase+10);
      printf("buf=%s\n",buf);*/
  munmap(pbase, filesz);
  // shm_unlink("/shm1");
  return 0;
}