使用fstream写入文件

Question

I tried to write into a file with fstream using the following code. It accepts the first entry and when I hit Enter , it goes into an infinite loop to the menu instead of allowing me to enter my second and third entries.

How can I fix this?

#include <iostream>
#include <fstream>
#include <string>
#include <stdlib.h>
using namespace std;


struct Course { // structure definition

char cID[3]; 
char title[40];
int creaditHour;
};


void showChoices();

void writeCourse(fstream& file, char fileName[]);



 int main ()
 {   
 fstream database;
 char filename[]="course.dat";

 int choice;
 do
    {
    showChoices();
    cin >> choice;
    switch (choice)
    {
    case 1:
            //  function call to write courses data
            writeCourse(database, filename);
            break;

    case 2:
            // call function 
            break;
    case 3:
            // call function 
            break;
    case 4:
            // call function 
            break;
    case 5:
            // call function 
            break;
    case 6:

        exit(1);
            break;
    default:
        cout<<"invalid input"<<endl;
    }

    }while (choice !=6);

     getchar();
     return 0;
     }


     void showChoices()
      {
      cout<< "Menu"<< endl;
      cout<< "1 : Enter Courses Data"<< endl;
      cout<< "2 : Enter ...."<< endl;
      cout<< "3 : Enter....."<< endl;
      cout<< "4 : Display ..."<< endl;
      cout<< "5 : Display Course Data"<< endl;
      cout<< "6 : Exit"<< endl;
      cout<< "Enter your choice:";
      }


     void writeCourse(fstream& aFile, char filename[])
          {
              Course courseData= {};//initialization
              aFile.open(filename,std::ios::out);
                 if (!aFile)
                  {
                   cout << "file opened for writing failed" << endl;
                   exit (-1);
                   }
              cout << endl;
              cout << "Begin Writing of " << filename << endl;
          cout << "Enter course ID, title, and creadit Hour\n? " << endl;


         for (int count=0; count<3;count++)
              {
          cin >>courseData.cID>>courseData.title>>courseData.creaditHour;
              }
         aFile.close();
         cout << "File name " << filename << " closed" << endl;
         cout << endl;
         }

Answer 1

Because you input a wrong data type that you want to store. There's nothing wrong in the code.

courseDate.creadithour is an int from the Course struct, so when you input a char type, error loop comes.

My approach for this is to change all the built in type from the Course struct into string and determine the input whether it is a digit or a letter.

Answer 2

In the function writeCourse() , you need to remove the for loop around the input stream so that each field will be entered exactly once for each entry. Also, you need to write the output to the file course.dat so that each entered record is saved in that file. Make the file open mode as "append" so that all entries will be saved. Code works as below:

void writeCourse(fstream& aFile, char filename[])
{
    Course courseData;//initialization
    aFile.open(filename, std::fstream::out | std::fstream::app);
    if (!aFile)
    {
        cout << "file opened for writing failed" << endl;
        exit (-1);
    }
    cout << endl;
    cout << "Begin Writing of " << filename << endl;
    cout << "Enter course ID, title, and creadit Hour\n" << endl;

    cin >> &courseData.cID[0] >> &courseData.title[0] >> courseData.creaditHour;
    aFile << &courseData.cID[0] << endl;
    aFile << &courseData.title[0] << endl;
    aFile << courseData.creaditHour << endl;
    aFile.close();
    cout << "File name " << filename << " closed" << endl;
    cout << endl;
}