#include <sys/types.h>
#include <unistd.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <iostream>

using namespace std;

void ReverseFile(char *fromFile, char *toFile) {
  int fromFd = open(fromFile, O_RDONLY);
  if (fromFd < 0) {
    cerr << "Error opening " << fromFile << "\n";
    return;
  }
  int toFd = creat(toFile, 0666);
  if (toFd < 0) {
    cerr << "Error opening " << toFile << "\n";
    close(fromFd);
    return;
  }
  lseek(fromFd, (off_t)(-1), SEEK_END);
  while(1) {
    char ch;
    int n = read(fromFd, &ch, 1);
    n = write(toFd, &ch, 1);
    if (n < 0) {cerr << "Error\n"; exit(0);}
    if (lseek(fromFd, (off_t)(-2), SEEK_CUR) < 0) break;
  }
  close(toFd);
  close(fromFd);
}


main(int argc, char * argv[])
{
  if (argc != 3) {
    cerr << "Usage: a.out srcfile dstfile\n";
    exit(1);
  }
  ReverseFile(argv[1], argv[2]);
}