C++用户认证程序故障：含空格用户名登录失败

Root Cause #

Your login logic fails for usernames with spaces because:

• You're using spaces to separate usernames and passwords in the record.txt file. This creates ambiguity when usernames themselves contain spaces.
• The >> extraction operator stops reading at the first whitespace character. So when reading a username like "John Doe", it only captures "John", leaving "Doe" to be read as the password—this causes a mismatch with the actual password stored.

Solution #

To fix this, we'll:

1. Use a unique delimiter (tab character \t) instead of spaces to separate username and password in the file. This ensures we can reliably split the stored data into username and password.
2. Read the entire line from the file during login, then split it using the tab delimiter to get the full username and password.

Modified Code #

#include <iostream>
#include <algorithm>
#include <cctype>
#include <fstream>
#include <string>

using namespace std;

int main()
{
    string User_Option;

    cout << "Do you want to Login Or Signup" << endl << endl;
    getline(cin, User_Option);
    transform(User_Option.begin(), User_Option.end(), User_Option.begin(), ::toupper);

    string Username_In_System;
    string Password_In_System;
    string Username;
    string Password;

    if (User_Option == "SIGNUP" || User_Option == "SIGN UP"){
        ofstream RecordFile;
        RecordFile.open("record.txt");

        cout << endl << endl << "USER AUTHENTICATION" << endl;
        cout << endl << "|*****************|" << endl;
        cout << endl << "SIGN UP FORM" << endl;

        cout << endl << "Enter Username: " << endl;
        getline(cin, Username_In_System);

        cout << endl << "Enter Password: " << endl;
        cin >> Password_In_System;

        cout << endl << endl << "Registration Success" << endl;

        // Use tab as delimiter instead of spaces
        RecordFile << Username_In_System << "\t" << Password_In_System << endl;
        RecordFile.close();
    }
    else if (User_Option == "LOGIN" || User_Option == "LOG IN" || User_Option == "SIGNIN" || User_Option == "SIGN IN"){
        ifstream InputFile;
        InputFile.open("record.txt");

        cout << endl << endl << "USER AUTHENTICATION" << endl;
        cout << endl << "|*****************|" << endl;
        cout << endl << "SIGN IN FORM" << endl;

        cout << endl << "Enter Username: " << endl;
        getline(cin, Username);

        cout << endl << "Enter Password: " << endl;
        cin >> Password;

        string line;
        bool loginSuccess = false;
        // Read entire line from file
        if (getline(InputFile, line)) {
            // Split line at tab delimiter
            size_t tabPos = line.find('\t');
            if (tabPos != string::npos) {
                Username_In_System = line.substr(0, tabPos);
                Password_In_System = line.substr(tabPos + 1);
                // Check credentials
                if (Username_In_System == Username && Password_In_System == Password) {
                    loginSuccess = true;
                }
            }
        }

        if (loginSuccess) {
            cout << endl << "Login Success" << endl;
        } else {
            cout << endl << "Login Error" << endl;
        }

        InputFile.close();
    }
    else {
        cout << endl << "Input Error" << endl;
    }

    return 0;
}

Additional Notes #

• If you want to allow passwords with spaces in the future, you'll need to use getline for password input as well. However, this requires clearing the newline character left in the input buffer after previous cin operations (you can use cin.ignore() for this).
• Using a tab delimiter ensures that spaces in usernames don't interfere with splitting the stored credentials correctly.

内容的提问来源于stack exchange，提问作者Kingsford Quainoo