c++ - 在简单的文件处理程序中获得异常输出

Question

这段代码有什么问题？我正在尝试写入二进制文件 MCQ 类型问题例如，问题:如果一台计算机向其他计算机提供数据库服务，那么它将被称为？ 1.Web服务器 2.应用程序 3.数据库服务器 4.FTP服务器

编号:1

答案:3

.

.

.

但是我得到了异常的输出。请查看我提供评论的代码。该程序提出问题并将其写入二进制文件。id 自动递增，问题和答案由用户询问。如果问题是“x”，则程序停止，如果还有其他问题，它会要求答案并将所有三个 id、问题、答案设置为一个临时对象，然后将其写入文件。

程序在第一个问题和答案上运行良好，然后直接询问第二个答案的答案而不询问第二个问题。

#include <iostream>
#include <fstream>
#include<string.h>
#include<conio.h>


using namespace std;

class questions{    //start of class
                    //private members
int id; //identification number for question ( 1,2,3,....)
char ques[100]; //question
int ans;    //answer (1,2,3,4) MCQ
public: //public members

void displayques() //displays question
{
    cout<<ques; //the same
}
int getans()    //returns answer
{
    return ans; //the same

}

int getid() //returns id
{
    return id; //the same
}

void setques(char q[]) //set the given string in parameter to the question.
{
strcpy(ques,q);
}

void setid(int i) //set the given int as id
{
id=i;
}
void setans(int a) //set the given int as answer
{
ans=a;
}
};          //end of class questions

int main()  //start of main
{
    questions quesobj;  //create an object of class questions
ofstream quesfile;  //creates and object of class ofstream

quesfile.open("questions.dat",ios::out|ios::binary);    //opens questions.dar in output mode as binary with the object quesfile of ofstream


char ask='y';   //to stop the process when its changed to n
char tempques[100]; //to temporarily store the question
int tempid=1;   //to temporarily store the id, initially at 1, later is incremented
int tempans;    //to temporarily store the answer

while(ask!='n') //runs upto the the point when use wants to escape the loop
{


    cout<<"Question? or enter x to stop"<<endl; //asks the questions also ask if user want to escape can enter x
    gets(tempques); //gets the question in temporary variable
    cout<<"Question registered"<<endl;  //shows question is ready to be written
    if(strcmp(tempques,"x")==0)      //if user enter the question as x
    {
        ask='n'; //sets ask to n which will end the loop
    }
    else        //if user enters something else than x, it is considered the question
    {
            cout<<"Answer:"<<endl;  //ask for the answer
            cin>>tempans;   //stores answer in temporary variable
            cout<<"Answer registered"<<endl; //shows answer is ready to be written
            quesobj.setid(tempid);  //sets id to the temp object of the class questions
            quesobj.setques(tempques); //sets question to the temp object of the class questions
            quesobj.setans(tempans); //sets answer to the temp object of the class questions

       quesfile.write((char *)&quesobj, sizeof(quesobj));   //write the temp object of class questions to the binary file
       tempid++;   //tempid is incremented for the next loop so that every question has its own id

    }



} //end of while
quesfile.close();   // closes the file using the object of ofstream
}

输出:

Question? or enter x to stop
This is my first question?
Question registered
Answer:
2
Answer registered
Question? or enter x to stop
Question registered
Answer:
_

Answer 1

正如评论中所建议的那样，

---

你不应该混合使用 C 和 C++ style IO。
由于您的代码未在我的系统上编译，因此我稍微清理了您的代码。我已经对其进行了测试，它现在运行良好。

#include <iostream>
#include <sstream>
#include <fstream>
#include <string>

using namespace std;


int string_to_int(const string& str)
{
    stringstream ss(str);
    int str_int;
    ss >> str_int;
    return str_int;
}


class Question
{
    int id;
    string question_string;
    int answer;

public:

    void displayQuestion()
    {
        cout << question_string;
    }

    int getAnswer()
    {
        return answer;
    }

    int getId()
    {
        return id;
    }

    void setQuestion ( const string& question_string_)
    {
        question_string = question_string_;
    }

    void setId ( int id_ )
    {
        id = id_;
    }
    void setAnswer ( int answer_ )
    {
        answer = answer_;
    }

};


int main()
{
    Question question;
    ofstream question_file;

    question_file.open ( "questions.dat", ios::out | ios::binary );

    char option = 'y';
    string temp_question;
    int temp_id =1;
    int temp_answer;

    while ( option != 'n' )
    {
        cout << "Question? or enter 'x' to stop" << endl;
        getline(cin, temp_question);
        cout << "Question registered" << endl;

        if (temp_question == "x")
        {
            option = 'n';
        }
        else
        {
            cout << "Answer? :" << endl;
            string temp_answer_string;
            getline(cin, temp_answer_string);
            temp_answer = string_to_int(temp_answer_string);
            cout << "Answer registered" << endl;

            question.setId ( temp_id );
            question.setQuestion ( temp_question );
            question.setAnswer ( temp_answer );

            question_file.write ( ( char* ) &question, sizeof ( question ) );
            temp_id++;
        }
    }

    question_file.close();
}