fstream ios:app troubles

This is a discussion on fstream ios:app troubles within the C++ Programming forums, part of the General Programming Boards category; I have searched through many pages and have yet to find an answer... with fstream myfile; This snippet writes the ...

  1. #1
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    fstream ios:app troubles

    I have searched through many pages and have yet to find an answer...

    with
    fstream myfile;

    This snippet writes the line and works properly

    myfile.open("test.txt", ios:ut);
    myfile << "This is my second entry.\n";
    myfile.close();


    This snippet erases everything in the file (it will not append)

    myfile.open("test.txt", ios::app);
    myfile << "This is my second entry.\n";
    myfile.close();

    I understood that fstream will let you use both ifstream and ofstream functions (including append) Why does this not work?

  2. #2
    For Narnia! Sentral's Avatar
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    Code:
    ofstream file("BLAH.txt",ios::app);
    WOW! LOOK WHAT I FOUND!

    http://www.cprogramming.com/tutorial/lesson10.html
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  3. #3
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    I have already declared it as fstream...

    Here is the whole program -
    Code:
    #include <fstream>
    #include <iostream>
    using namespace std;
    
    int main() 
    {
    
        
        char buffer[256];
        fstream myfile;
        
        myfile.open("test.txt", ios::out);
        myfile << "This is my first entry.\n";
        myfile.close();
        
        myfile.open("test.txt",ios::in);
        myfile.getline(buffer,100);
        cout << "The file originally contained:  " << buffer << "\n";
        myfile.close();
        
        myfile.open("test.txt", ios::app);// <--- There it is!!!
        myfile << "This is my second entry.\n";
        myfile.close();
        
        
        myfile.open("test.txt",ios::in);
        myfile.getline(buffer,100);
        cout << "The file now contains:  " << buffer << "\n";
        myfile.close();
        
        myfile.open("test.txt", ios::out);
        myfile << "This is my third entry.\n";
        myfile.close();
        
        myfile.open("test.txt",ios::in);
        myfile.getline(buffer,100);
        cout << "The file now contains:  " << buffer << "\n";
        myfile.close();
     
    return 0;
    }
    Why, exactly, will ios::in ios:ut work, but ios::app wil not?
    Last edited by Ken Fitlike; 10-04-2006 at 02:15 PM. Reason: added code tags

  4. #4
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    restated

    Let me restate, I don't think I can use a real ofstream now (to append), because myfile is already declared as a type fstream. The compiler won't let me cross use them.

  5. #5
    For Narnia! Sentral's Avatar
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    Ifstream is used for reading in files, ofstream is used to create them. You need to change your code, and read the link I gave you.
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  6. #6
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    Maybe I am just daft. The post you linked does not help. I am not using ifstream and ofstream... I am using fstream.

    The documentation that I am using says that:

    when "myfile" is declared as type "fstream" you are able to:

    myfile.open("whatever.txt",ios::in);
    myfile.open("whatever.txt",ios:ut);
    myfile.open("whatever.txt",ios::trunc);
    myfile.open("whatever.txt",ios::app);

    You see, I cant simply ofstream now, becuase "myfile" is of type fstream...

    Why do all the above examples work except the :app one?

  7. #7
    For Narnia! Sentral's Avatar
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    I understand it's of type fstream. So just change it to 'ofstream' and it will work. Follow the link, unless you have to do it using fstream. I've never used fstream, so I can't help with that, ofstream always worked just fine for me.
    Videogame Memories!
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    Share your experiences with us now!

    "We will game forever!"

  8. #8
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    Thank you much for your help. A very funny thing happened...


    when I changed:
    myfile.open("test.txt", ios::app);

    to:
    myfile.open("test.txt", ios:ut|ios::app);

    it started working. This completely wrecks me, as I can't see why. If I just use out, it erases everything else. If I just use app, it does nothing at all. When I use them both with an "|" it works.

    Again, thanks much. I am such a noob.

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