Question

我还是一个学习C ++的学生，我只是一个初学者。这是我的代码。这里的问题是最后的用户名和密码在文本文件中被保存两次。虽然我已经使用系统打开我的其他程序，因为我只是一个初学者，这是我能想出的最简单的方法。谢谢你的帮助。

// Projectregus.cpp : Defines the entry point for the console application.


#include "stdafx.h"
#include<iostream>
#include<fstream>
#include<time.h>
#include<cstdlib>
#include<conio.h>
using namespace std;
ifstream users;
class usersdet
{
  public:
char username[100];
char password[100];
double score;
void assignpass(char pass[])
 {
    int k;
    for (int j = 0; pass[j] != '\0'; ++j)
    {
        password[j] = pass[j];
            k = j;
    };
    password[k+1] = '\0';
 }
}A,B,C;
  class quiz
{
  public:
char question[10000];
char option1[1000];
char option2[1000];
char option3[1000];
char option4[1000];
char answer;
};
 /* ***************************************Function login() defination begins here**************************************** */
 void login() 
  {
   cout << "Sign In to continue....\nEnter your username:";
   cin >> B.username;
   int flag = 0, choice;
   users.open("E:\\Users\\Utkarsh\\Documents\\Visual Studio    2015\\Projects\\Project\\Debug\\userdat.txt", ios::in|ios::binary);
if (!users.is_open())
{
    cout << "fatal error!";
    exit(0);
}
while (!users.eof())
{
    users.read((char *)&A, sizeof(A));
    if (strcmp(A.username, B.username) == 0)
    {
        flag = 1;
        break;
    }
    else flag = 0;
};
if (flag == 0)
{
    cout << "Account not found!";
    cout << "\nMENU:\n1.Want to make new account?\t2.Retry?";
    cin >> choice;
    switch (choice)
    {
    case 1:system("start E:\\Users\\Utkarsh\\Documents\\Projectnewus.exe");
        exit(0);
        break;
    case 2:system("start E:\\Users\\Utkarsh\\Documents\\projectregus.exe");
        exit(0);
        break;
    default: cout << "Wrong input!";
        exit(0);
    }
}
cout << "Enter password:";
char pass[100];
int i = 0;
char a;
for (i = 0;;)
{
    a = _getch();
    if ((a>='a' && a<='z') || (a>='A'&&a <='Z') || (a>='0'&& a<='9'))
    {
        pass[i] = a;
        ++i;
        cout << "*";
    }
    if (a =='\b' && i>= 1)
    {
        cout << "\b \b";//rub the character behind the cursor.
        --i;
    }
    if (a == '\r')//if enter is pressed
    {
        pass[i] = '\0';
        break;
    }
}
cout << endl;
B.assignpass(pass);
if (strcmp(A.password, B.password) == 0)
{
    cout << "Login successful!";
    cin.ignore();
    getchar();
}
else
{
    cout << "Login failure !";
    cin.ignore();
    getchar();
    exit(0);
    }
  users.close();
 }
    /* *********************************QUIZGAME function defination     here**************************************************** */
   void quizgame()
  {
     B.score = 0;
     cout << "\nLets begin the QUIZ " << A.username;
     cout << "\n Your last score was:" << A.score;
     getchar();
     ifstream game; 
     cout << "Which quiz do you want to play?\n1.General Knowledge\n2.General Science\n";
     int choice2;
     cin >> choice2;
     cin.ignore();
     switch (choice2)           //choice of file to be opened
     {
case 1:game.open("E:\\Users\\Utkarsh\\Documents\\Visual Studio 2015\\Projects\\Project\\Debug\\quizGK.txt", ios::in | ios::binary);
    if (!game.is_open())
    {
        cout << "fatal error!";
        exit(0);
    }
    break;
case 2:game.open("E:\\Users\\Utkarsh\\Documents\\Visual Studio 2015\\Projects\\Project\\Debug\\quizGS.txt", ios::in | ios::binary);
    if (!game.is_open())
    {
        cout << "fatal error!";
        exit(0);
    }
    break;
default:cout << "Wrong input!!";
    exit(0);
};
quiz X;
int qno, seedval, count, verification[50], verificationflag = 1, iotemp = 0, ioflag = 0, gamecounter = 0;
for (int in = 0; in < 6; ++in)          //initialises verification[]
    verification[in] = 0;
char choice1 = 'y';
time_t t;
seedval = (unsigned)time(&t);
srand(seedval);
while (choice1 == 'y'&& gamecounter != 6)
{
    while (verificationflag == 1)           //Assures unique question
    {
        qno = (rand() % 6) + 1;

        for (int io = 0; io < 6; ++io)
        {
            if (verification[io] == qno)
            {
                ioflag = 1;
            }
        }

        if (ioflag == 0)
        {
            verification[iotemp] = qno;
            verificationflag = 0;
            ++iotemp;
        }
        ioflag = 0;

    }

    game.seekg(0);
    for (count = 0; count < qno; ++count)
    {
        game.read((char *)&X, sizeof(X));
    }
    system("cls");
    cout << "Your " << gamecounter + 1 << " Question\n\n";
    cout << X.question << endl << X.option1 << endl << X.option2 << endl << X.option3 << endl << X.option4 << endl << "Enter answer:";
    char answer;
    int score = 0;
    cin >> answer;
    cin.ignore();
    if ((answer == X.answer) || (answer == tolower(X.answer)))
    {
        cout << "correct answer";
        ++B.score;
    }
    else
    {
        cout << "Wrong answer/nCorrect answer is "<<X.answer;

    }
    cout << "\nYour current score:" << B.score;
    cout << "\nWant to play more?(y/n)";
    cin >> choice1;
    verificationflag = 1;
    ++gamecounter;
    if (gamecounter == 6)
        cout << "GAME ENDED!";

   }
   game.close();
 }
  /* ********************************************MAIN BEGINS     HERE******************************************************** */
 void main() 
{
system("cls");
login();
system("cls");
quizgame();
users.open("E:\\Users\\Utkarsh\\Documents\\Visual Studio 2015\\Projects\\Project\\Debug\\userdat.txt", ios::in|ios::binary);
ofstream temp;
temp.open("E:\\Users\\Utkarsh\\Documents\\Visual Studio 2015\\Projects\\Project\\Debug\\temp.txt",ios::out|ios::binary);
if (!temp.is_open())
{
    cout << "fatal error!";
    exit(0);
}
if (!users.is_open())
{
    cout << "fatal error!";
    exit(0);
}
users.seekg(0);
while (!users.fail())
{
    users.read((char*)&C, sizeof(C));
    if (strcmp(C.username, A.username) != 0)
        temp.write((char*)&C, sizeof(C));
}
A.score = B.score;
temp.write((char*)&A, sizeof(A));
users.close();
temp.close();
cout << A.username << endl << A.password << endl << A.score;
remove("E:\\Users\\Utkarsh\\Documents\\Visual Studio 2015\\Projects\\Project\\Debug\\userdat.txt");
rename("E:\\Users\\Utkarsh\\Documents\\Visual Studio 2015\\Projects\\Project\\Debug\\temp.txt", "E:\\Users\\Utkarsh\\Documents\\Visual Studio 2015\\Projects\\Project\\Debug\\userdat.txt");
system("pause");


}






 what i am getting in my text file is:
muskaan ÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌmuskaan23 ÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌ        sample ÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌsample23 ÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌ        sample ÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌsample23 ÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌ        utkarsh ÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌutkarsh23 ÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌ      ð?
  Here muskaan,utkarsh and sample is username i entered using another program

Answer 1

您期望eof函数预测未来，并告诉您未来的读取是成功还是失败。不幸的是，该功能仅报告过去。

假设您有一个列表“apple”，“orange”，“pear”。你读“苹果”并处理它。你读“橙色”并处理它。你读“梨”并处理它。然后你再次尝试阅读，然后失败。但是你不检查读取是否成功，所以你再次处理“梨”。然后你突破了循环，因为你点击了文件的末尾。

忘记检查eof。它没用。相反，当读取失败时突破循环。当然，如果读取失败，不会处理缓冲区中您在上一次读取中已经处理过的过时数据。

为什么数据输入两次？

1 个答案: