Answer to Question #42790 in C++ for ahmed

Question

how to do a login function using primary index and the primary index is the username?

Answer 1

The primary indexes(usernames) are stored in “index.dat”. The user information is stored in “users.dat”
in the format “username|password” (e.g. “jack|qwerty123”). “Login()” is the
login function.
Code

#include<iostream>
#include<string>
#include<fstream>
#include<list>
#include<map>
 
using namespacestd;
 
// filenames
conststring fnindex = "index.dat";
conststring fnusers = "users.dat";
 
// lists of usernamesand passwords
list<string>users;
map<string,string> passwords;
 
boolLoadUsernames() {
    ifstream findex(fnindex);
    string username;
 
    // users are added to usernamelist
    if (findex.is_open()) {
        while (getline(findex,username)) {
            users.push_back(username);
        }
        findex.close();
        return true;
    }
    else {
        return false;
    }
}
 
boolLoadPasswords() {
    ifstream fusers(fnusers);
    string line;
    string username;
    string password;
 
    // users with passwords are addedto username list
    if (fusers.is_open()) {
        while (getline(fusers,line)) {
            intpos = line.find("|");
            username =line.substr(0, pos);
            password =line.substr(pos+ 1);
            passwords.emplace(username,password);
        }
        fusers.close();
        return true;
    }
    else {
        return false;
    }
}
 
// login function
voidLogin() {
    list<string>::iteratorpos;
 
    string username;
    string password;
    bool logged = false;
 
    LoadUsernames();
 
    while (!logged) {
        cout << "Enterusername:" << endl;
        cin >>username;
 
        cout << "Enterpassword:" << endl;
        cin >>password;
 
        // username ischecked 
        pos =find(users.begin(),users.end(),username);
        if (pos!= users.end()) {
            // user informationis loading
            LoadPasswords();
 
            //password is checked
            if (passwords[username] ==password) {
                cout << "Youare logged in" << endl;
                logged = true;
            }
            else {
                cout << "Thepassword is incorrect" <<endl;
            }
        }
        else {
            cout << "Theusername is incorrect" <<endl;
        }
    }
}
 
intmain() {
    Login();
 
    return 0;
}