ofstream Odeint output to txt file - c++

Question

I try to run this example from the ODEINT library to solve ODE. It just runs fine, but instead of cout the results to screen, I want to write them to a file. I add this ofstream to the code under write_cout function but it only writes the last line of result to the file and not all.
Do you have any idea about this? Thanks
#include <iostream>
#include <boost/numeric/odeint.hpp>
#include <fstream>
using namespace std;
using namespace boost::numeric::odeint;
void rhs( const double x , double &dxdt , const double t )
{
dxdt = 3.0/(2.0*t*t) + x/(2.0*t);
}
void write_cout( const double &x , const double t )
{
cout << t << '\t' << x << endl;
cout<<"alo"<<endl;
ofstream buckyFile ("tuna.txt");
buckyFile<<t <<'\t'<<x<<endl;
}
// state_type = double
typedef runge_kutta_dopri5< double > stepper_type;
int main()
{
double x = 0.0;
integrate_adaptive( make_controlled( 1E-12 , 1E-12 , stepper_type() ) ,
rhs , x , 1.0 , 10.0 , 0.1 , write_cout );
}

Answer 1

Or even better
struct stream_writer
{
std::ostream& m_out;
stream_writer( std::ostream& out ) : m_out( out ) {}
void operator()( const double &x , const double t )
{
m_out << t << "\t" << x << "\n";
}
};
int main()
{
double x = 0.0;
ofstream fout( "tuna.txt" );
integrate_adaptive( make_controlled( 1E-12 , 1E-12 , stepper_type() ) ,
rhs , x , 1.0 , 10.0 , 0.1 , stream_writer( fout ) );
}

Answer 2

ofstream buckyFile ("tuna.txt");
opens a new file tuna.txt each time the function is entered, overriding what ever was there before.
A quick fix would be to use a
static ofstream buckyFile ("tuna.txt");
instead.