#include <unistd.h>
#include <fcntl.h>
#include <stdio.h>

void set(int fd, size_t elem, int value) {
  //lseek(fd,elem * sizeof(int), SEEK_SET); non-atomic
  //write(fd, &value, sizeof (int));
  pwrite(fd, &value, sizeof (int), elem * sizeof(int));
}

int get(int fd, size_t elem) {
  //lseek(fd, elem * sizeof(int), SEEK_SET);
  int value = 0;
  pread(fd, &value, sizeof (int), elem * sizeof(int));
  return value;
}

int main() {
  int fd = open("mem", O_RDWR|O_CREAT, 0666);
  if (fd < 0) {
    perror("mem");
    return 1;
  }

  for (int i = 0; i < 100; i++) {
    set(fd, i*1000, i+1);
  }
  for (int i = 0; i < 100000; i++) {
    int x = get(fd,i);
    if (x != 0) {
      printf("mem[%d]=%d\n", i, x);
    }
  }  
  close(fd);
}