[Solved] Reading an input file in C++

Question

doing

while (fin >> name >> var1 >> var2 >> var3)
{
    cout << name << var1 << var2 << var3 << endl;
}

you rewrite all the time on the same variables, you need to put the value in a vector as you say in your question

you need also to check if each input is correct, currently you do not detect the invalid input

and of course you need to check you open the file

Example :

#include <iostream>
#include <fstream>
#include <string>
#include <vector>

int main()
{
  std::ifstream fin("inputFile.txt");

  if (!fin.is_open()) {
    std::cerr << "cannot open inputFile.txt" << std::endl;
    return -1;
  }

  int numberOfStates, numberOfSymbols, numberOfFinalStates;

  if ((! (fin >> numberOfStates >> numberOfSymbols >> numberOfFinalStates))
      || (numberOfStates < 0)
      || (numberOfSymbols < 0)
      || (numberOfFinalStates < 0)) {
    std::cerr << "invalid file" << std::endl;
    return -1;
  }

  // final states are int, so memorize them in a vector of int
  // because their number is known I can size it rather than 
  // to 'push_back' each value
  std::vector<int> finalStates(numberOfFinalStates);

  for (int & ft : finalStates) {
    if (! (fin >> ft)) {
      std::cerr << "invalid file reading final states" << std::endl;
      return -1;
    }
  }

  int numberOfTransitions;

  if (!(fin >> numberOfTransitions) || (numberOfTransitions < 0))  {
    std::cerr << "invalid file reading the number of transitions" << std::endl;
    return -1;
  }

  // you say a transition contains 2 int and a char,
  // I define a structure for
  // i1 i2 and c are 'poor' names but I don't know their goal
  struct Transition {
    int i1, i2; 
    char c;
  };

  // the transitions saved in a vector
  std::vector<Transition> transitions(numberOfTransitions);

  for (Transition & tr : transitions) {
    if (!(fin >> tr.i1 >> tr.i2 >> tr.c)) {
      std::cerr << "invalid file reading transitions" << std::endl;
      return -1;
    }
  }

  // print to check

  std::cout << "numberOfStates=" << numberOfStates << std::endl;
  std::cout << "numberOfSymbols=" << numberOfSymbols << std::endl;
  std::cout << "numberOfFinalStates=" << numberOfFinalStates << "\nfinalStates:";
  for (int ft : finalStates) 
     std::cout << ' ' << ft;
  std::cout << std::endl;
  std::cout << "numberOfTransitions=" << numberOfTransitions
    << "\ntransitions:" << std::endl;
  for (const Transition & tr : transitions)
    std::cout << '\t' << tr.i1 << ' ' << tr.i2 << ' ' << tr.c << std::endl;

  return 0;
}

Compilation and execution :

pi@raspberrypi:/tmp $ g++ -pedantic -Wextra -Wall a.cc
pi@raspberrypi:/tmp $ cat inputFile.txt
10 
3 
1 
9 
12 
0 1 f 
0 3 f 
1 2 a 
2 9 f 
3 4 f 
3 8 f 
4 5 b 
5 6 f 
6 7 a 
8 9 f 
pi@raspberrypi:/tmp $ ./a.out
invalid file reading transitions

The error comes because the file contains only 10 transitions rather than 12 expected, modifying the file to expect 10 transitions :

pi@raspberrypi:/tmp $ ./a.out
numberOfStates=10
numberOfSymbols=3
numberOfFinalStates=1
finalStates: 9
numberOfTransitions=10
transitions:
    0 1 f
    0 3 f
    1 2 a
    2 9 f
    3 4 f
    3 8 f
    4 5 b
    5 6 f
    6 7 a
    8 9 f
pi@raspberrypi:/tmp $

Accepted Answer