My function don't take over the variable value from other function - c++

Question

I have a program to create a phone book in a file. Some of my functions don't work or don't work properly.
user.h
#pragma once
#include <string>
#include <vector>
using namespace std;
class User
{private:
string firstname, lastname, country, city, street;
string phone;
public:
string prefix;
void ReadAllUsers(User[], int&);
void SaveUser(User, int&);
void SaveToFile(const User[], int);
void AddName(User[], int&);
void ListAllUsers(const User[], int&);
void Prefix(User, int);
void ChangePhone(User[], int&);
void Help();
void DeleteUser(User[], int&);
bool Search(string x)
{
return (phone.find(x) != string::npos);
}
};
user.cpp
#include "User.h"
#include <iostream>
#include <fstream>
#include <string>
#include <vector>
#pragma warning(disable:4996)
using namespace std;
const string PHONEBOOK_FILENAME = "phonebook.txt";
void User::Help()
{cout<<"\nWELCOME TO THE APPLICATION!\n";
cout<<"Press 0 to display on the screen all records that are saved in the file(phonebook.txt)\n";
cout<<"Press 1 to add 1 or more new record(s) in file(phonebook.txt)\n";
cout<<"Press 2 to delete permanently a record from file(phonebook.txt)\n";
cout<<"Press 3 to sort users from file(phonebook.txt) by name and display them on the screen\n";
cout<<"Press 4 to edit a user phone number and save it after in file(phonebook.txt)\n";
cout<<"Press 5 for help\n";
cout<<"Press 6 to exit the application\n";
}
void User::ReadAllUsers(User people[], int &num_people)
{
ifstream f;
f.open(PHONEBOOK_FILENAME.c_str());
if (f.fail())
{
cout << "Unable to open file " << endl;
return ;
}
int i = 0;
while (!f.eof() && i < 100)
{ getline(f, people[i].firstname);
getline(f, people[i].lastname);
getline(f, people[i].phone);
getline(f, people[i].country);
getline(f, people[i].city);
getline(f, people[i].street);
i++;
}
num_people = i;
f.close();
}
//Add country prefix to the phone number
void User::Prefix(User person, int num_people)
{string filecountry;
ifstream f;
f.open("prefix.txt");
{
while (getline(f, filecountry))
{
if (person.country == filecountry )
{
f.ignore();//next line
f >> person.prefix;
}
}
f.close();
}
}
void User::SaveUser(User person, int &num_people)
{
ofstream f(PHONEBOOK_FILENAME.c_str(), ios::app ) ;
if (f.fail())
cout << "Unable to open file " << endl;
else
f << person.firstname << " " << person.lastname << " " << person.country << " " << person.city << " " << person.street << " " << person.prefix << "-" << person.phone << endl;
cout << "\nThe user was added\n";
}
//Save data after a modification or after a user delete
void User::SaveToFile(const User people[], int num_people)
{ofstream f;
f.open(PHONEBOOK_FILENAME.c_str());
for(int i = 0; i < num_people; i++)
{
f << people[i].firstname << " " << people[i].lastname << " " << people[i].country << " " << people[i].city << " " << people[i].street << " " << people[i].prefix << " " << people[i].phone << endl;
}
}
// Read user data from the keyboard, add a new contact to the array
void User::AddName(User people[],int &num_people)
{User person;
cout <<"Enter the user's first name: ";
cin >> person.firstname;
cout <<"Enter the user's last name: ";
cin >> person.lastname;
cout <<"Enter the user's country: ";
cin >> person.country;
cout <<"Enter the user's city: ";
cin >> person.city;
cout <<"Enter the user's street: ";
cin >> person.street;
cout <<"Enter the user's phone number: ";
cin >> person.phone;
Prefix(person, num_people);
cout <<"The prefix is " << person.prefix;
for(int i = 0; i < num_people; i++)
{
if( i + 1 == num_people)
people[num_people] = person;
}
SaveUser(person, num_people);
num_people++;
}
// Ask the for person's name to change, find the person in the array and
// change it to the new phone number. Then save the new data to file by
// calling SaveToFile.
void User::ChangePhone(User people[], int &num_people)
{
User person;
int count;
cout <<"Enter name to change: ";
cin >> person.firstname;
for(count = 0; count < num_people; count++)
{
if(people[count].Search(person.firstname))
{ cout <<endl<< people[count].firstname<<endl;
cout <<"Current number"<<people[count].phone;
cout << "\nNew number: ";
cin >> people[count].phone;
SaveToFile(people,num_people);
cout <<"\n\nNew number Saved.";
return;
}
}
if(count = num_people)
cout <<"\nName not found.\n";
}
void User::DeleteUser(User people[], int &num_people)
{string phone;
int count = 0;
ifstream f;
f.open("phonebook.txt");
cout << "Input the phone of user that you want to delete ";
cin >> phone;
for(count = 0; count < num_people; count++)
{
if(people[count].Search(phone))
{ cout <<endl<< people[count].phone<<endl;
people[count].firstname = people[count].lastname = people[count].phone = people[count].country = people[count].city = people[count].street = " ";
}
SaveToFile(people,num_people);
cout <<"\n\nUser deleted.";
return;}
f.close();
}
The function Prefix()(this is to add automatically a country prefix for phone number, this is read from a file) is working but the value of person.prefix it's not taken by SaveUser(), so the value is not wrote in file.The function SaveToFile() save all users on single line in file.
And functions ChangePhone() and DeleteUser don't working.

Answer 1

The problem is that void User::Prefix(User person, int num_people) takes person by value, so it makes a copy of the person, changes the copy, then the copy goes away when the function ends. The original was never changed.
Instead, you want:
void User::Prefix(User & person, int num_people)
To have a reference to the person specified, which will be affected by the changes you make inside the function.
Also, I recommend you change your saveuser to be:
void User::SaveUser(User const & person, int &num_people) const
just to avoid making extra copies of the User object, but it's not incorrect the way you currently have it, I don't think.