How to fill structs within a class from a file?

Question

I have an assignment where we need to create a class object that has many different variables, one of which being a struct. I can't figure out how to fill the struct from my setter function. I've attached some codes snippets I've pulled out of my code. my count_file_line function returns an int value of however many lines are in a txt file. I'm also really new to coding and have been struggling so if it's an obvious answer, sorry

When I run the program and try to cout teachers[I].password from within the setter function, nothing shows up (the "Flag" does show up)

struct teacher{
  int id;
  string password;
  string first_name;
  string last_name;
};

void University::set_teachers(ifstream& inFile){
    int amountOfTeachers = count_file_lines(inFile);
    this->teachers = new teacher[amountOfTeachers];

    for(int i = 0; i < amountOfTeachers; i++){
        inFile >> teachers[i].password;
        inFile >> teachers[i].first_name;
        inFile >> teachers[i].last_name;
cout << "Flag" << endl;

    }
}

Answer 1

What you're trying to accomplish is a "de-serialization" of a sequence of teacher objects.

You may be interested in:

Is it possible to serialize and deserialize a class in C++?

for some general-purpose solutions. Note those may (or may not) be a bit "heavy-weight" for what you need to achieve.

Answer 2

Example of using tell, don't ask:

#include <iostream>
using std::cout, std::cerr, std::endl;

#include <iomanip>
using std::setw, std::setfill;

#include <fstream>
using std::ifstream, std::istream; // std::ofstream;

#include <sstream>
using std::stringstream;

#include <string>
using std::string, std::to_string;

#include <cstdint>

#include <cassert>


// stub - this function implemented and tested elsewhere
int count_file_lines(ifstream& inFile)
{
   if (!inFile.good())
      cerr << "\n  !infile.good()" << endl;
   return 5; // for test purposes
}


struct teacher
{
private:
   int    id;       // unique number in record order
   string password;
   string first_name;
   string last_name;
   static int ID;  // init value below

   // note: On my system each string is 32 bytes in this object,
   //       regardless of char count: the chars are in dynamic memory

public:
   teacher() : id(++ID) // password, first_name, last_name
      { }               //        default init is empty string

   ~teacher() = default; // do nothing

   void read(istream& inFile)  // tell instance to read next record
      {
         inFile >> password;
         inFile >> first_name;
         inFile >> last_name;
      }

   void show()
      {
         cout << "\n  show  id:" << id
              << "\n  pw      :" << password
              << "\n  fn      :" << first_name
              << "\n  ln      :" << last_name
              << endl;
      }

};

int teacher::ID = 0;  // compute unique ID number for each record

And a demo of input and output (teacher::read(), teacher::show())

Note use of "stringstream ss;". It is filled using a for loop, and passed to each teacher object using "teacher.read()".

Then the teacher values are echo'd to output using "teacher.show()"

class F834_t
{
   teacher* teachers = nullptr; // do not yet know how many
   ifstream inFile;             // declared, but not opened
   uint     amountOfTeachers = 0; 

   stringstream ss;     // for debug / demo use


public:
   // use default ctor, dtor
   F834_t() = default;
   ~F834_t() = default;

   int exec(int , char** )
      {
         // open infile to count lines

         amountOfTeachers = static_cast<uint>(count_file_lines(inFile)); // use working func
         cout << "\n  teacher count: " << amountOfTeachers << "\n ";   // echo

         // init ss with 5 values
         for (uint i=1; i<=amountOfTeachers; ++i)
            ss << " pw" << i << " fn" << i << " ln" << i << "  ";
         cout << ss.str() << endl;

         teachers = new teacher[amountOfTeachers]; // allocate space, invoke default ctor of each
         assert(teachers);
         cout << "\n     teachers: " << setw(4) << sizeof(teachers) << "  (pointer bytes)"
              << "\n    a teacher: " << setw(4) << sizeof(teacher)  << "  (teacher bytes)"
              << "\n  size of all: " << setw(4) << (amountOfTeachers * sizeof(teacher))
              << "  ( " << setw(3) << sizeof(teacher) << " * " <<  setw(3) << amountOfTeachers << ')'
              << endl;

         // reset stream to start of inFIle, maybe close/open inFile

         for (uint i=0;i<amountOfTeachers; ++i)
         {
            assert(ss.good()); // (inFile.good());

            teachers[i].read(ss); // (inFile);  // tell the object to read the file
         }

         for (uint i=0;i<amountOfTeachers; ++i)
         {
            teachers[i].show(); // tell the object to show its contents
         }

         return 0;
      }
}; // class F834_t


int main(int argc, char* argv[])
{
   F834_t f834;

   return f834.exec(argc, argv);
}

Output - note that a much simplified input stream is created on the fly, and is echo'd early in this output.

  teacher count: 5
  pw1 fn1 ln1   pw2 fn2 ln2   pw3 fn3 ln3   pw4 fn4 ln4   pw5 fn5 ln5  

     teachers:    8  (pointer bytes)
    a teacher:  104  (teacher bytes)
  size of all:  520  ( 104 *   5)

  show  id:1
  pw      :pw1
  fn      :fn1
  ln      :ln1

  show  id:2
  pw      :pw2
  fn      :fn2
  ln      :ln2

  show  id:3
  pw      :pw3
  fn      :fn3
  ln      :ln3

  show  id:4
  pw      :pw4
  fn      :fn4
  ln      :ln4

  show  id:5
  pw      :pw5
  fn      :fn5
  ln      :ln5