# Writing and reading data from files

Here we will use the `it_file` class to store some data. The program `write_it_file.cpp` looks as follows:

    #include <itpp/itcomm.h>

    using namespace itpp;

    int main()
    {
      // Declare the it_file class
      it_file ff;

      // Open a file with the name "it_file_test.it"
      ff.open("it_file_test.it");

      // Create some data to put into the file
      vec a = linspace(1, 20, 20);

      // Put the variable a into the file. The Name("a") tells the file class
      // that the next variable shall be named "a".
      ff << Name("a") << a;

      // Force the file to be written to disc. This is useful when performing
      // iterations and ensures that the information is not stored in any cache
      // memory. In this simple example it is not necessary to flush the file.
      ff.flush();

      // Close the file
      ff.close();

      // Exit program
      return 0;
    }

When you run this program you will obtain a file called `it_file_test.it` in your current directory. You can read the file into Matlab/Octave to view the data by using the following commands:

    itload('it_file_test.it')
    figure(1); clf;
    plot(a)

Note: Make sure that `$PREFIX/share/itpp` is in your Matlab/Octave path and that you run the code above from the directory where `it_file_test.it` is located (`$PREFIX` is the IT++ installation prefix; `/usr/local` by default).

The IT++ program `read_it_file.cpp` that reads the file and prints its content can look like this:

Here is the output of the program:

    a = [1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20]