Reading from a files as a string

Hey there,

I'm writing a chatting system, like an instant messenger, that runs over my school's shared HD (accessed by all computers on the network). I use Ubuntu at home, and the school runs XP, so I do all my compiling and testing at school, and all the writing at home. The concept I need help with makes up a large portion of the program, and if I'm doing it wrong, I'll basically have to rewrite it... so help here would save a lot of potential trouble.

"users.data" is the file where all the username and password information is stored (writing an encrypter for it later). Every even numbered line is a username, and every odd numbered line is a password. The entered username is passed to this function, it searches the file for that username, then saves the following line, which should be the password to the specified username, as the password. It then calls the function which handles prompting the user for the correct password. Will this code work as I need it to? Specifically the 'for' loop.

Code:

---

void getPass(string userName) {
        string tempName, password;

        ifstream userNameDB("users.data");

        for (int i = 0; i != userNameDB.eof(); i = i + 2) {
                userNameDB >> tempName;

                if (tempName == userName) {
                        i++;
                        userNameDB >> password;
                        userNameDB.close();
                        logInPASS(userName, password);
                }
                       
        }
       
        userNameDB.close();
        cout << endl << "Error fetching password for " << userName << "." << endl;
        writeError(1);
       
        return -1;
}

---

Thanks in advance.

Have you tried the code yourself?

Code:

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i != userNameDB.eof()

---

this will almost certainly prevent the fist iteration of the loop from working since eof() is zero and i is zero -> statement is false -> no entry into the loop. Using eof() to control a loop is wrong, and here your usage of eof() is also very wrong. [eof() does not return the number of elements or size of the file - it return false if the last read from the file was NOT a failure.]

Instead of using eof(), you should use the "success of reading data".

Further, if we have:

Code:

---

// users.data
John
xyzzy
Tim
foobar
Mary
blahblah

---

What will happen if the username is Mary on the second time of the loop [assuming the above eof() problem is fixed].


--
Mats

Quote:

---

Originally Posted by matsp

What will happen if the username is Mary on the second time of the loop [assuming the above eof() problem is fixed].

---

Depends, is the first line of the file considered line 0 or line 1?

Would it start checking the passwords as usernames?

Also, I can't find anything about how to check the success of reading data, like you suggested. I remember Elysia had something about it in his/her sig with a link, but I never looked.

http://faq.cprogramming.com/cgi-bin/...&id=1043284351
Btw, you can use a virtual machine for testing your app at home.
Although the link is for C, the same solution applies to C++ as well (reading using the >> operator).

Setting up a virtual machine seems complicated, but I'll look into it

Meanwhile, would this work?

Code:

---

void getPass(string userName) {
        string tempName, password;

        ifstream userNameDB("users.data");

        for (int i = 0; (userNameDB >> tempName); i = i + 2) {
                userNameDB >> tempName;

                if (tempName == userName) {
                        i++;
                        userNameDB >> password;
                        userNameDB.close();
                        logInPASS(userName, password);
                }
                       
        }
       
        userNameDB.close();
        cout << endl << "Error fetching password for " << userName << "." << endl;
        writeError(1);
       
        return -1;
}

---

Quote:

---

Originally Posted by PAragonxd

Setting up a virtual machine seems complicated, but I'll look into it

---

Well, I imagine it might be on Linux, but on the other hand, it can't be that difficult.

Quote:

---

Meanwhile, would this work?

Code:

---

void getPass(string userName) {
        string tempName, password;

        ifstream userNameDB("users.data");

        for (int i = 0; (userNameDB >> tempName); i = i + 2) {
                userNameDB >> tempName;

                if (tempName == userName) {
                        i++;
                        userNameDB >> password;
                        userNameDB.close();
                        logInPASS(userName, password);
                }
                       
        }
       
        userNameDB.close();
        cout << endl << "Error fetching password for " << userName << "." << endl;
        writeError(1);
       
        return -1;
}

---

---

Nope, it will absolutely not work, because you're reading twice.
userNameDB >> tempName; // Reads user
userNameDB >> tempName; // Reads pass
if (tempName == userName) // Fails

This program should work just fine with your Windows XP machine - there is nothing machine/OS specific in the way your code works, so why not just run it as a Windows console application. That is a 10x simpler solution than virtual machines or such, and as long as you are not depending on OS-specific functionality (that is, you are using standard C/C++ functionality), it shouldn't make any difference.

--
Mats

Quote:

---

Originally Posted by matsp

This program should work just fine with your Windows XP machine

---

I run Linux, so I'd have to run Windows windowed :P.

Quote:

---

Originally Posted by Elysia

Nope, it will absolutely not work, because you're reading twice.
userNameDB >> tempName; // Reads user

---

So could I use the same reading as both the loop condition AND for checking against the entered username?

Code:

---

void getPass(string userName) {
        string tempName, password;

        ifstream userNameDB("users.data");

        for (int i = 0; (userNameDB >> tempName); i = i + 2) {
                if (tempName == userName) {
                        i++;
                        userNameDB >> password;
                        userNameDB.close();
                        logInPASS(userName, password);
                }
                       
        }
       
        userNameDB.close();
        cout << endl << "Error fetching password for " << userName << "." << endl;
        writeError(1);
       
        return -1;

}

---

That was the point, so yeah :)
But I wonder if you could run Wine on the app, as well... Maybe it would work since your program is not very complicated.

Awesome, thanks.

I've tried running simple programs in Wine, but they don't work; I assume it's because they are run in the windows console, not an included interface.

Wine is supposed to run Win apps exactly as they would on Windows, GUI and all (not limited to console).
Though that doesn't mean I know why it doesn't work.

Hm, I'd work on figuring it out, but I'm going back to using Windows as soon as I can. I had to reformat and reinstall Windows due to a virus, and in reformatting I lost the drivers to my Ethernet hookup. Gateway only supplies the drivers I need for Vista, and I used XP. Either upgrading to Vista or getting a new computer.. it's about that time anyway.

Depends on how you're running them through wine. wine will NOT spawn a terminal window for console-based applications. Either run the program through the terminal, or run wine's 'cmd.exe' and run your program from there.

If it is graphical, check the wine logs or output from when you run it via a terminal, ie "wine ~/.wine/c_drive/myprogram.exe"

Ok, so I got it the wrong way around with where you have Linux vs Windows. But I assume this is a console application for Windows, correct? [Because I'd expect some more experience in file handling before you start doing GUI apps - but I could be wrong].

If so, running a linux text based app should be no different from using a console app in Windows.

And if it is a GUI app, the code you are working on right NOW is not GUI-related, so it could easily be made into a text-mode app for the time being for testing purposes - that may take a tiny bit of time to make up the framework, but it's good practice and you'd be able to test your code without having to mess about with wine or such.

--
Mats