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; // filenamesconststring fnindex = "index.dat";conststring fnusers = "users.dat"; // lists of usernamesand passwordslist<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 functionvoidLogin() {    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;}