ifstream 似乎不在 switch 语句中工作

Question

I've been having difficulties in searching a text in a text file when I choose case 4 or 'show video details'. It seems that ifstream in a switch statement is not working. This is my code:

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

using namespace std;

int main()
{
    int choice;
    //4
    string line;
    bool iffound = false;
    string id1;
    ifstream file("test.txt");

menu:
    cout << "MENU" << endl
         << endl;
    cout << "[1] NEW VIDEO" << endl;
    cout << "[2] RENT A VIDEO" << endl;
    cout << "[3] RETURN A VIDEO" << endl;
    cout << "[4] SHOW VIDEO DETAILS" << endl;
    cout << "[5] DISPLAY ALL VIDEOS" << endl;
    cout << "[6] CHECK VIDEO AVAILABILITY" << endl;
    cout << "[7] CUSTOMER'S MAINTENANCE" << endl;
    cout << "[8] EXIT PROGRAM" << endl;
    cout << "Choice: ";

    cin >> choice;

    switch (choice)
    {
    case 1:
        break;
    case 2:
        break;
    case 3:
        break;
    case 4:
    {
        file.open("test.txt");
        cout << "<< SHOW VIDEO DETAILS >>" << endl
             << endl;
        cout << "Enter Movie ID: ";
        cin >> id1;
        string idnum1 = "VIDEO ID: " + id1;
        cout << idnum1 << endl;

        while (file.good())
        {
            getline(file, line);
            if (line == idnum1)
            {
                iffound = true;
                for (int i = 0; i <= 3; i++)
                {
                    getline(file, line);
                    cout << line << endl;
                }
                break;
            }
        }
        file.close();

        if (iffound != true)
        {
            cout << "Video not found!" << endl;
        }
    }
    break;
    case 5:

        break;
    case 6:
        break;
    case 7:
        break;
    case 8:
        break;
    }
}

And this is my text file:

VIDEO ID : 1
MOVIE TITLE     : IT
GENRE           : HORROR
PRODUCTION      : NEW LINE CINEMA
NUMBER OF COPIES: 0
it.jpg
VIDEO ID : 2
MOVIE TITLE     : THE CALL
GENRE           : HORROR
PRODUCTION      : YONG FILM
NUMBER OF COPIES: 3
thecall.jpg
VIDEO ID : 3
MOVIE TITLE     : I AM LEGEND
GENRE           : HORROR
PRODUCTION      : VILLAGE ROADSHOW
NUMBER OF COPIES: 6
iamlegend.jpg

When I input a valid Id , for instance, 1 , it outputs 'video not found', when clearly the Id is present.

But when I try this code, where there is no switch statement, it works:

int main()
{
    ifstream file("test.txt");
    string line;
    bool find = false;
    string id;
    string img;

    cout << "Enter movie ID: ";
    cin >> id;
    string idnum = "VIDEO ID : " + id;
    cout << idnum << endl;

    while (file.good())
    {
        getline(file, line);
        if (line == idnum)
        {
            find = true;
            for (int i = 0; i < 4; i++)
            {
                getline(file, line);
                cout << line << endl;
            }
            getline(file, img);
            cout << img;
        }
    }
    file.close();

    if (find != true)
    {
        cout << "Movie Not Found" << endl;
    }
    return 0;
}

But I need to run it in a switch statement.

Answer 1

It's not related to the switch , the problem (aside from the already identified missing space in the concatenated string) is that you are reopening the already opened file a second time (notice that you don't do that in the working code snippet).

What happens is that the error state of the stream buffer will be set to failbit and good() will be returning false , everything inside the while loop will not be executed.

Open it only once and your code will work fine.

Instead of:

ifstream file("test.txt");

Use:

ifstream file;

Or just remove:

file.open("test.txt");

---

And of course add the space to the concatenated string:

string idnum1 = "VIDEO ID : " + id1;
                         ^

Live demo

---

I should point out that you should revisit your usage of using namespace std; check this post for reasons and alternatives:

Why is "using namespace std;" considered bad practice?

Answer 2

Change

string idnum1 = "VIDEO ID: " + id1;

to

string idnum1 = "VIDEO ID : " + id1;

Adds one space.