C++如何实现简易登录注册系统

fstream

struct

#include <iostream>
#include <fstream>
#include <string>
#include <vector> // 后面可能会用到，先放着

// 用户信息结构体
struct User {
    std::string username;
    std::string password;

    // 构造函数，方便初始化
    User(std::string u = "", std::string p = "") : username(u), password(p) {}
};

// 文件名常量
const std::string USER_DB_FILE = "users.txt";

// 注册功能
bool registerUser() {
    std::string username, password;
    std::cout << "--- 注册新用户 ---\n";
    std::cout << "请输入用户名: ";
    std::cin >> username;
    std::cout << "请输入密码: ";
    std::cin >> password;

    // 检查用户名是否已存在
    std::ifstream inFile(USER_DB_FILE);
    std::string line;
    while (std::getline(inFile, line)) {
        size_t commaPos = line.find(',');
        if (commaPos != std::string::npos) {
            std::string existingUsername = line.substr(0, commaPos);
            if (existingUsername == username) {
                std::cout << "错误：用户名 '" << username << "' 已存在，请换一个。\n";
                inFile.close();
                return false;
            }
        }
    }
    inFile.close(); // 关闭读取流

    // 将新用户写入文件
    std::ofstream outFile(USER_DB_FILE, std::ios::app); // append 模式
    if (outFile.is_open()) {
        outFile << username << "," << password << "\n";
        outFile.close();
        std::cout << "用户 '" << username << "' 注册成功！\n";
        return true;
    } else {
        std::cerr << "错误：无法打开用户数据库文件进行写入。\n";
        return false;
    }
}

// 登录功能
bool loginUser() {
    std::string username, password;
    std::cout << "--- 用户登录 ---\n";
    std::cout << "请输入用户名: ";
    std::cin >> username;
    std::cout << "请输入密码: ";
    std::cin >> password;

    std::ifstream inFile(USER_DB_FILE);
    if (!inFile.is_open()) {
        std::cerr << "错误：无法打开用户数据库文件进行读取。可能还没有用户注册。\n";
        return false;
    }

    std::string line;
    while (std::getline(inFile, line)) {
        size_t commaPos = line.find(',');
        if (commaPos != std::string::npos) {
            std::string storedUsername = line.substr(0, commaPos);
            std::string storedPassword = line.substr(commaPos + 1);

            if (storedUsername == username && storedPassword == password) {
                std::cout << "登录成功！欢迎，" << username << "！\n";
                inFile.close();
                return true;
            }
        }
    }
    inFile.close();
    std::cout << "登录失败：用户名或密码不正确。\n";
    return false;
}

// 主菜单函数
void showMenu() {
    int choice;
    do {
        std::cout << "\n--- 简易登录注册系统 ---\n";
        std::cout << "1. 注册\n";
        std::cout << "2. 登录\n";
        std::cout << "3. 退出\n";
        std::cout << "请选择操作: ";
        std::cin >> choice;

        switch (choice) {
            case 1:
                registerUser();
                break;
            case 2:
                loginUser();
                break;
            case 3:
                std::cout << "感谢使用，再见！\n";
                break;
            default:
                std::cout << "无效的选择，请重新输入。\n";
        }
    } while (choice != 3);
}

// main 函数
int main() {
    showMenu();
    return 0;
}

registerUser

loginUser

fstream