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Old 08-17-2005, 01:39 AM   #1
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Registered: Aug 2004
Distribution: Gentoo
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How do I delete a line in a file with fstream (C++)?

I have been spending a considerable amount of time trying to figure this out. I have been trying to write a program that creates a config file with entries separated by new lines, and have been trying to figure out how to delete a line -- like this:

Figure this out
Write such-and-such
Pay such-and-such


Figure this out
Pay such-and-such

I want the line deleted determined by user input. Here is my code so far. Right now I just made it so that it would delete and rebuild each line; I have not discovered a more efficient way to write it. The only problem is it produces a garbled output to the text file. Can anyone help me figure out what I am doing wrong?

int remove()
        //Open file -- getconfigfile() gets the path for the config file
        fstream stodo;, fstream::in | fstream::out );

        //char array line is stored in
        char line[255];
        short int choice;
        //function that lists items
        cout << "Choose an item to remove\n";
        cin >> choice;

        //Delete and rebuild lines before choice
        for(short int num = 1; num != choice; num++)
                stodo.getline(line, 256);
                stodo.ignore(256, '\n');
                stodo << line;
        //delete choice
        stodo.ignore(256, '\n');
        //delete and rebuild lines after choice
                stodo.getline(line, 256);
                stodo.ignore(256, '\n');
                stodo << line;
        //close file
        stodo << flush;
        return 0;
Any help would be appreciated. Apologies if I leave some detail out.

Last edited by CrazyHoboMan; 08-17-2005 at 12:41 PM.
Old 08-17-2005, 06:55 AM   #2
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Registered: Jul 2004
Location: Denmark
Distribution: Ubuntu, Debian
Posts: 1,524

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I know what you're doing wrong: you're not putting code tags around your code.

[ c o d e ]
my code
[ / c o d e ]
Delete the spaces.

I can't recall the exact C++ semantics of streams used both for input and output, so I can't say what you're doing wrong, but I can suggest an alternative solution:
1) slurp the file (read it into a vector).
2) delete an element from the vector.
3) write it back.

hth --Jonas
Old 08-17-2005, 12:47 PM   #3
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Registered: Aug 2004
Distribution: Gentoo
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Don't really know much about vectors, but I'll look into it. Thanks for pointing me in some direction (I was getting a bit lost). Also i fixed the code block... didn't know it wouldn't format right.

Last edited by CrazyHoboMan; 08-17-2005 at 12:48 PM.
Old 08-18-2005, 02:06 AM   #4
Registered: Jul 2004
Location: Santiago, Chile
Distribution: Ubuntu
Posts: 410

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If the file is too big, using vectors wouldn't be a good idea, I think.

If the problem is reading/writing in the same file, you can always modify a little your program to create a copy of the file, delete the original and rename the copy...


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