#include <iostream>  // so I can do reasonable i/o

#include <sys/types.h>  // open at least
#include <sys/stat.h>   // open
#include <fcntl.h>      // open
#include <unistd.h>     // read

#include <string.h>  // strcmp
#include <stdio.h>   // perror

using namespace std;

void SeekAndTell(int fd);
void MyWrite(int fd);
void MyRead(int fd);
void DumpFile(int fd);

int main() {
   int theFD, 
       openFlags;

   mode_t filePerms;
   openFlags = O_CREAT | O_RDWR | O_TRUNC;

   filePerms = S_IRUSR | S_IWUSR | 
               S_IRGRP | S_IROTH ; 

   theFD = open("SeekFile", openFlags, filePerms);

   if (theFD == -1){
       perror("Could not open the output file ");
       return 1;
   }

   // initiall fill the file with some data.
   char c = 'A';
   int i;

   for(i=0;i<10;i++) {
      write(theFD, &c, sizeof(char));
      c = c + 1;
   }

   char action;
   do {
      cout << " r - read, w - write, d - dump, q - quit" << endl;
      cout << "Enter your action (r,w,d,q) -> ";
      cin >> action;
      switch (action) {
         case 'r': MyRead(theFD);   break;
	 case 'w': MyWrite(theFD);  break;
	 case 'd': DumpFile(theFD); break;
      }
   } while (action != 'q'); 

   close(theFD);

   return 0;
}

void SeekAndTell(int fd) {
    off_t  toPos, len;

    len = lseek(fd, 0, SEEK_END);
    cout << "The file is " << len << " bytes long" << endl;
    cout << endl;

    do {
        cout << "Enter a position to seek to => ";
        cin >> toPos;
    } while (toPos >= len or toPos < 0);

    cout << "\tSeeking to " << toPos << " byte" << endl;
    lseek(fd, toPos, SEEK_SET);
    return;
}

void MyRead(int fd) {
   char letter;

   SeekAndTell(fd);
   read(fd, &letter, sizeof(char));
   cout <<"\t" << letter << " is at that position" << endl;

   return;
}

void MyWrite(int fd) {
   char letter;

   SeekAndTell(fd);

   cout << "Enter a letter to save there => ";
   cin >> letter;
   write(fd, &letter, sizeof(char));

   return ;
}

void DumpFile(int fd){
    off_t len;
    int i;
    char c;
    len = lseek(fd, 0, SEEK_END);

    lseek(fd, 0, SEEK_SET);
    for(i=0;i<len;i++) {
       read(fd, &c, sizeof(char));
       cout << c;
    }
    cout << endl;

    return;
}