OOP can't get value from a class - c++

Question

So I read a file in a function and set values to a class. I would like to read those same values in another function (another .cpp file) and I can't get it to work.
This is the code where I read values from .txt file. This seems to work. I can cout the value that I read.
#include "branjeDatoteke.h"
#include "parametri.h"
#include <iostream>
#include <fstream>
#include <string>
#include <cstring>
using namespace std;
void branjeDatoteke() {
Parametri pin[101];
string line;
ifstream myfile("pin.txt");
if (myfile.is_open())
{
for (int i = 0; i <= 100 && getline(myfile, line); i++)
{
pin[i].setPin(line);
// cout << pin[i].readPin() << endl;
//cout << line << '\n';
}
myfile.close();
// cout <<"tole more delat: "<< pin[2].readPin() << endl;
}
else cout << "Unable to open file";
}
And this is the code where I want to get the same values again, but cout is not working. I just get blank console where the cout should be.
#include <iostream>
#include "pin.h"
#include "parametri.h"
#include <string>
#include "branjeDatoteke.h"
using namespace std;
void pinPass() {
Parametri pin[101];
string pinKoda;
branjeDatoteke();
cout << pin[0].readPin() << endl;
cout << "Vnesite pin: ";
cin >> pinKoda;
for (int i = 0; i <= 100; i++) {
if (pin[i].readPin() == pinKoda) {
cout << pin[i].readPin() << endl;
cout << "KODA JE PRAVILNA" << endl;
}
else if (i > 100) {
cout << "kode ni v sistemu" << endl;
}
}
}

Answer 1

Assuming your Parametri class is correct, the issue is you are using local variables so they are initialised every time you call the function. They are allocated on the stack, locally for the calling function and can't be used outside of the function that declares them, at least not the way you're doing it. If you call the function twice you also have to assume all local variables must be reinitialised. One way you could solve this would be promoting your pin variable to global, like so:
// your_file_one.cpp
Parametri pin[101];
void PinPass() {
...
}
If you want to use it in another cpp file, then you have to redeclare the variable in the other file as well, like follows:
// your_file_two.cpp
extern Parametri pin[101];
The extern keyword specifies the variable was declared in another compilation unit - for simplicity let's imagine each C++ file which is not a header file as a separate compilation unit.
So your code will look like:
#include "branjeDatoteke.h"
#include "parametri.h"
#include <iostream>
#include <fstream>
#include <string>
#include <cstring>
using namespace std;
Parametri pin[101];
void branjeDatoteke() {
string line;
ifstream myfile("pin.txt");
if (myfile.is_open())
{
for (int i = 0; i <= 100 && getline(myfile, line); i++)
{
pin[i].setPin(line);
// cout << pin[i].readPin() << endl;
//cout << line << '\n';
}
myfile.close();
// cout <<"tole more delat: "<< pin[2].readPin() << endl;
}
else cout << "Unable to open file";
}
And
#include <iostream>
#include "pin.h"
#include "parametri.h"
#include <string>
#include "branjeDatoteke.h"
using namespace std;
extern Parametri pin[101];
void pinPass() {
string pinKoda;
branjeDatoteke();
cout << pin[0].readPin() << endl;
cout << "Vnesite pin: ";
cin >> pinKoda;
for (int i = 0; i <= 100; i++) {
if (pin[i].readPin() == pinKoda) {
cout << pin[i].readPin() << endl;
cout << "KODA JE PRAVILNA" << endl;
}
else if (i > 100) {
cout << "kode ni v sistemu" << endl;
}
}
}
There are better ways of using global variables than declaring them many times and you may want to research these if you're going to write bigger programs. Also global variables are very useful in certain instances but must not be abused as they can make bigger applications much more difficult to read and maintain.

Answer 2

The Parametri array in your pinPass function is empty(or more precisely , has garbage values).You call the branjeDatoteke function from within pinPass , the
branjeDatoteke function then creates it's own Parametri array (WHICH IS DIFFERENT from the one in your pinPass function),reads the values from the file and displays it via cout.
When branjeDatoteke is done with it's work , all the local variables of that function , inlcuding the Parametri array are destroyed and your program jumps back to the pinPass function.
To do what you're trying to achieve , which is , presumably , have a common array for both the functions, you can either pass the array from pinPass to branjeDatokete , or you can tell branjoDatokete to allocate an array on the heap and then return a pointer to it.I guess the first approach fits better for what you're trying to achieve.