file i/o and classes

This is a discussion on file i/o and classes within the C++ Programming forums, part of the General Programming Boards category; i have a program that it a little wacked (cause i suck at programming)...anyway, i need some clarification on input ...

  1. #1
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    file i/o and classes

    i have a program that it a little wacked (cause i suck at programming)...anyway, i need some clarification on input and output to/from a file.

    if you declare:
    //code
    fstream myfile;
    myfile=open("myfile.txt", ios::in);
    //endcode

    i understand that this will open "myfile.txt", but does it create that file if it doesn't already exist?

    *sigh*...tonight ends the night of the endless summer.
    eat, drink and be merry. for tomorrow: we party.

  2. #2
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    also...

    the thing that's kind of messing me up is that i have file being opened and read by the constructor in one class, and then being written to by the deconstructor in that same class...so i dont think that the deconstructor is being called...it could also be that i just dont understand deconstructors.
    eat, drink and be merry. for tomorrow: we party.

  3. #3
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    I'm pretty sure that it will not create one. I think because you are looking to get input FROM the file that it will return an invalid handle if it doesn't exist. Here are some other things to consider when dealing with files. If you just want to get input from a file you can do this.

    ifstream fin( "data.txt" );

    or for output

    ofstream fout( "data.txt" );

    When you specify fstream you are saying that you may do input AND output.

    Also, if you do not wish that the file be created when attempting to output to a file, you can specify ios::nocreate and if the file doesn't exist it will not be created.
    "...the results are undefined, and we all know what "undefined" means: it means it works during development, it works during testing, and it blows up in your most important customers' faces." --Scott Meyers

  4. #4
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    hmm

    so, i actually want to be using a fstream...like this:

    //code
    fstream myfile;
    myfile=open("myfile.txt");
    //

    will this create the file if that file is not found?
    eat, drink and be merry. for tomorrow: we party.

  5. #5
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    >i understand that this will open "myfile.txt", but does it create that file if it doesn't already exist?

    No. To create it if it doesn't exist use either:

    Code:
    myfile.open("myfile.txt", ios::in | ios::out);
    
    Or:
    
    myfile.open("myfile.txt", ios::in);
    if (!myfile.is_open())
       myfile.open("myfile.txt", ios::out);
    
    And there's also:
    myfile.open("myfile.txt", ios::app);
    to append to a file

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