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:

#include <itpp/itcomm.h>

using namespace itpp;

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

  // Open the file "it_file_test.it" for reading
  ff.open("it_file_test.it");

  // Read the variable a from the file. Put result in vector a.
  vec a;
  ff >> Name("a") >> a;

  // Print the result
  std::cout << "a = " << a << std::endl;

  // Exit the program
  return 0;
}

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]