Tail.cpp

// Copyright (c) 2013 Elements of Programming Interviews. All rights reserved.

#include <algorithm>
#include <cassert>
#include <fstream>
#include <iostream>
#include <string>

using std::cout;
using std::endl;
using std::fstream;
using std::ios;
using std::ofstream;
using std::string;
using std::to_string;

// @include
string tail(const string& file_name, int tail_count) {
  fstream file_ptr(file_name.c_str());

  file_ptr.seekg(0, ios::end);
  int file_size = file_ptr.tellg(), newline_count = 0;
  string output;  // stores the last tail_count lines.
  // Reads file in reverse looking for '\n'.
  for (int i = 0; i < file_size; ++i) {
    file_ptr.seekg(-1 - i, ios::end);
    char c;
    file_ptr.get(c);
    if (c == '\n') {
      ++newline_count;
      if (newline_count > tail_count) {
        break;
      }
    }
    output.push_back(c);
  }
  // Reverse the output string using the reverse() function.
  // The arguments are iterators to the start and end of string object.
  reverse(output.begin(), output.end());
  return output;
}
// @exclude

void small_test() {
  ofstream ofs("test_Tail.txt");
  ofs << "A free soft copy sample of Elements of Programming Interviews can be found at bit.ly/epi-sample" << endl;
  ofs << endl;
  ofs << "The core of Elements of Programming Interviews (EPI) is a collection of 300 problems with detailed solutions, including over 150 figures and 250 tested programs. The problems are representative of the questions asked at interviews at the most exciting companies. They are well-motivated, thought-provoking and fun to solve!" << endl;
  ofs << endl;
  ofs << "EPI includes a summary of the nontechnical aspects of interviewing, including common mistakes, strategies for a great interview, the interviewer's perspective, negotiating the best offer, and much more." << endl;
  ofs << endl;
  ofs << "Since different candidates have different time constraints, EPI includes a study guide with several study scenarios, ranging from weekend Hackathon to semester long preparation with a recommended a subset of problems for each scenario." << endl;
  ofs << endl;
  ofs.close();
  auto res = tail("test_Tail.txt", 3);
  assert(!res.compare("\nSince different candidates have different time constraints, EPI includes a study guide with several study scenarios, ranging from weekend Hackathon to semester long preparation with a recommended a subset of problems for each scenario.\n\n"));
  remove("test_Tail.txt");
}

int main(int argc, char* argv[]) {
  small_test();
  cout << "Usage: file name and tail count" << endl;
  int tail_count = 10;
  string file_name;
  if (argc == 2) {
    file_name = argv[1];
  } else if (argc == 3) {
    file_name = argv[1];
    tail_count = atoi(argv[2]);
  } else {
    exit(1);
  }
  string output = tail(file_name, tail_count);
  cout << output;
  string command = "tail -n " + to_string(tail_count) + " " + file_name;
  cout << "command = " << command << endl;
  system(command.c_str());
  return 0;
}