Output format to file

This is a discussion on Output format to file within the C++ Programming forums, part of the General Programming Boards category; Hi I am writing data from two vectors to a file in the following way: Code: std::ofstream data_file("data.txt", ios::out); j ...

  1. #1
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    Output format to file

    Hi

    I am writing data from two vectors to a file in the following way:

    Code:
    std::ofstream data_file("data.txt", ios::out);
    j = Y.begin();
    for(i=X.begin(); i<X.end(); i++)
    {
    vectorFile << *i << "\t" << *j << "\n";
    j++;
    }
    data_file.close();
    However, is there a way to format the data output? E.g., such t hat there is 8 numbers in total, i.e. of the form

    123.45678
    12.345678
    1.2345678
    ....

    I have tried with
    Code:
    	std::cout.setf ( std::ios_base::right, std::ios_base::basefield );
    	std::cout.width ( 5 );
    but that didn't do any difference.

    Best,
    Niles.
    Last edited by Niels_M; 04-02-2012 at 02:02 PM.

  2. #2
    Registered User hk_mp5kpdw's Avatar
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    Code:
    #include <iostream>
    #include <iomanip>
    
    ...
    
    double d = 123.45678;
    
    ...
    
    std::cout << d << std::endl;
    std::cout << std::setprecision(8) << d << std::endl;
    Output:
    Code:
    123.457
    123.45678
    "Owners of dogs will have noticed that, if you provide them with food and water and shelter and affection, they will think you are god. Whereas owners of cats are compelled to realize that, if you provide them with food and water and shelter and affection, they draw the conclusion that they are gods."
    -Christopher Hitchens

  3. #3
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    You do know that setting formatting options for cout will not affect your file stream (vectorFile) correct? Also note that setw() is not "sticky", meaning that it only works once you need to reissue the setw() each time you need it. Also when setting the flags don't forget the ios::showpoint and ios::fixed. See this link for manipulators.

    Jim

  4. #4
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    If not cout, then what should I be setting the options for?

    Best,
    Niles.

  5. #5
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    If you want to alter how your file looks then modify the file stream. If you want to alter how cout displays the information then use cout. These are separate streams, changes to one does not change the other.

    Jim

  6. #6
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    I see, thanks!

    Best,
    Niles.

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