Implementing a check function using a vector in C++? - c++

Question

#include "User.h"
#include <vector>
using namespace std;
User::User(){
username;
password;
}
User::User(const string& uname, const string& pass){
username = uname;
password = pass;
}
string User::get_username() const{
return username;
}
bool User::check(const string &uname, const string &pass) const{
if(username == uname && password == pass){
return true;
}
else{
return false;
}
}
In user.cpp, I am attempting to use the User::check function to check a username and password against a vector in board.cpp.
#include "BBoard.h"
#include "User.h"
#include <fstream>
#include <algorithm>
using namespace std;
User user_l;
BBoard::BBoard(){
title = "Default BBoard";
vector<User> user_list;
User current_user;
vector<Message> message_list;
}
BBoard::BBoard(const string &ttl){
title = ttl;
}
void BBoard::setup(const string &input_file){
ifstream fin;
string name, pass;
fin.open(input_file.c_str());
while(fin.good()){
fin >> name >> pass;
user_l = User(name, pass);
user_list.push_back(user_l);
}
}
void BBoard::login(){
string sn, pw;
cout << "Welcome to " << title;
bookmark:
cout << "\nEnter your username ('Q' or 'q' to quit): ";
getline(cin, sn);
if((sn == "Q" || sn == "q")){
cout << "Bye!";
exit(0);
}
cout << "Enter your password: ";
getline(cin, pw);
for(int i = 0; i < user_list.size(); i++){
if(user_list.at(i).check(sn, pw) == true){
cout << "Welcome back " << sn << "!" << endl;
User copy(sn, pw);
User current_user = copy;
}
else{
cout << "Invalid Username or Password!" << endl;
goto bookmark;
}
}
}
However, I am having great difficulty implementing the check function in login as my for loop in login doesn't seem to do anything and just simply runs along. How can I use implement check into my login function so that when the user enter a username and password in sn and pw, I can use check to reference it against the vector user_list to determine if it is a valid login or not?
Edit:
header for board
#ifndef BBOARD_H
#define BBOARD_H
#include <iostream>
#include <string>
#include <vector>
#include "User.h"
#include "Message.h"
using namespace std;
class BBoard{
private:
string title;
vector<User> user_list;
User current_user;
vector<Message> message_list;
public:
BBoard();
BBoard(const string &ttl);
void setup(const string &input_file);
void login();
};
#endif
and the header for user
#ifndef USER_H
#define USER_H
#include <string>
using namespace std;
class User{
private:
string username;
string password;
public:
User();
User(const string& uname, const string& pass);
string get_username() const;
bool check(const string &uname, const string &pass) const;
//void set_password(const string &newpass);
};
#endif
Edit:
new login
void BBoard::login(){
string sn, pw;
cout << "Welcome to " << title;
bookmark:
cout << "\nEnter your username ('Q' or 'q' to quit): ";
getline(cin, sn);
if((sn == "Q" || sn == "q")){
cout << "Bye!";
exit(0);
}
cout << "Enter your password: ";
getline(cin, pw);
for(int i = 0; i < user_list.size(); i++){
if(user_list.at(i).check(sn, pw) == true){
cout << "Welcome back " << sn << "!" << endl;
User copy(sn, pw);
User current_user = copy;
break;
}
else{
cout << "Invalid Username or Password!" << endl;
while(user_list.at(i).check(sn, pw) == false){
getline(cin, sn);
if((sn == "Q" || sn == "q")){
cout << "Bye!";
exit(0);
}
cout << "Enter your password: ";
getline(cin, pw);
}
}
}
}

Answer 1

While I didn't want to write your assignment for you, there are too many errors to comment on as there seems to be some misunderstanding of member initialization and variable scope. Below I've edited your code for you to compare what might be missing...I don't have a compiler handy right now so I can't 100% test this but this is your assignment so I recommend you try the code out yourself :)
BBoard.h
#ifndef BBOARD_H
#define BBOARD_H
#include <string>
#include <vector>
#include "User.h"
#include "Message.h"
class BBoard{
private:
std::string title;
std::vector<User> user_list;
User current_user;
std::vector<Message> message_list;
public:
BBoard();
BBoard(const std::string &ttl);
void setup(const std::string &input_file);
void login();
};
#endif
User.h
#ifndef USER_H
#define USER_H
#include <string>
class User{
private:
std::string username;
std::string password;
public:
User();
User(const std::string& uname, const std::string& pass);
std::string get_username() const;
bool check(const std::string &uname, const std::string &pass) const;
//void set_password(const string &newpass);
};
#endif
User.cpp
#include "User.h"
#include <vector>
User::User() : username(), password() { }
User::User(const std::string& uname, const std::string& pass)
: username(uname), password(pass)
{
}
std::string User::get_username() const {
return username;
}
bool User::check(const std::string &uname, const std::string &pass) const
{
return ((username == uname) && (password == pass));
}
BBoard.cpp
#include "BBoard.h"
#include "User.h"
#include <fstream>
#include <algorithm>
BBoard::BBoard()
: title("Default BBoard"),
user_list(),
current_user(),
message_list()
{
}
BBoard::BBoard(const std::string &ttl)
: title(ttl),
user_list(),
current_user(),
message_list()
{
}
void BBoard::setup(const std::string &input_file)
{
std::string name, pass;
std::ifstream fin(input_file.c_str());
while(fin.good()) {
fin >> name >> pass;
user_list.push_back(User(name, pass));
}
fin.close();
}
void BBoard::login()
{
std::string sn, pw;
bool found = false;
std::cout << "Welcome to " << title << std::endl;
while (!found) {
found = false;
std::cout << "\nEnter your username ('Q' or 'q' to quit): ";
std::cin >> sn; std::cin.clear();
if((sn == "Q" || sn == "q")){
std::cout << "Bye!";
break;
}
std::cout << "Enter your password: ";
std::cin >> pw; cin.clear();
std::vector<User>::iterator itr = user_list.begin();
while (itr != user_list.end() {
if (itr->check(sn, pw)) {
std::cout << "Welcome back " << sn << "!" << std::endl;
// this code does nothing except create a local scope (in this 'if' block only) User object
User copy(sn, pw);
User current_user = copy;
// copy and current_user are destroyed after the break statement
found = true;
break;
}
}
if (!found) { std::cout << "Invalid Username or Password!" << std::endl; }
}
}
I hope that can help

Answer 2

One solution is to add an operator == for your User class and call std::find().
#include <algorithm>
class User
{
std::string uname;
std::string password;
public:
bool operator ==(const User& u) const
{ return uname == u.uname && password == u.password; }
//...
};
void BBoard::login()
{
User testUser;
// assign testUser the credentials they are logging in with
//...
// check if user is in our vector
std::vector<User>::iterator itFound = std::find(user_list.begin(),
user_list.end(), testUser);
if ( itFound != user_list.end())
{
// user exists
}
}
Using find_if() if not allowed to change User class:
#include <algorithm>
struct FindUser
{
User u;
FindUser(const User& theUser) : u(theUser) {}
bool operator()( const User& theUser) const
{ return u.check(theUser); }
};
void BBoard::login()
{
User testUser;
// assign testUser the credentials they are logging in with
//...
// check if user is in our vector
std::vector<User>::iterator itFound = std::find_if(user_list.begin(),
user_list.end(),
FindUser(testUser));
if ( itFound != user_list.end())
{
// user exists
}
}

Answer 3

I believe your problem comes from the fact that you are declaring and initializing the same variables at different scopes so while you think you're modifying a member variable, you're in fact modifying a local variable which gets deleted as soon as it gets out of scope.
For example you have a member variable called current_user in the BBoard class. In the constructor you call User current_user; which in no way affects the member variable, but instead creates a new local variable with the same name. You then do the same thing in several places.
Once a member variable has been declared in the header, you use it by calling its name and without specifying its type again. Therefore to assign to current_user member variable in a function you shouldn't write:
User current_user = copy; // Declares new local variable
but instead write:
current_user = copy; // Uses a member variable declared in the header
As you make this mistake in several places, I assume this is causing your problem, as you are probably using a local variable while you mean to use a member one. Please check your code and make sure you're not redeclaring member variables at local scope.
To avoid confusion it is a good practice at add a prefix or a postfix to the name of your member variables so they are easily spotted. E.g. you could call your current_user member variable: m_current_user or current_user_.