Getting ifstream from istream and calling functions via overloaded >> operator

Question

I've created an object, PDBParser, to extract information from a PDB file. Now I am trying to overload the >> and << operators so that I can use them from the main as so:

inFile >> MyPDBParser;
outfile << MyPDBParser;

I've got the << operator all set, but I can't seem to get the >> operator to work properly.

Here is the .h file for the PDBParser class to give you a better idea of what's going on:

#include <iostream>
#include <cstdlib>
#include "FloatArray.h"
#include "IntArray.h"
#include "Atom.h"
#include "AtomArray.h"

using namespace std;

class PDBParser
{
friend ostream& operator<<(ostream& _ostream, PDBParser &rhs);
friend istream& operator>>(istream& _istream, PDBParser &rhs);


public:
    PDBParser();
    PDBParser(string atom1, string atom2, int separation);
    PDBParser(const PDBParser& orig);
    virtual ~PDBParser();

    void grabAtoms(ifstream &infile);
    void findAtoms();

    void setAtom1(string rhs);
    void setAtom2(string rhs);
    void setSeparation(int rhs);

    string getAtom1();
    string getAtom2();
    int getSeparation();



private:
    string atom1s;
    string atom2s;
    int separation;

    AtomArray *atoms1;
    AtomArray *atoms2;
    AtomArray *matches1;
    AtomArray *matches2;


    FloatArray *x1;
    FloatArray *y1;
    FloatArray *z1;
    FloatArray *x2;
    FloatArray *y2;
    FloatArray *z2;

    IntArray *allsequence;


    ifstream backupinfile;


    void trim(string &rhs);
    void incrementArrays(int newElements);


};

Essentially what I need the >> operator to do is get the infile from the istream and then call the grabAtoms(infile) and findAtoms() functions for this instance of the PDBParser object.

Here's what I have now, which doesn't work. Please forgive the commented lines, as they were things I was attempting to make work. I tried adding the backupinfile object to the PDBParser class just to make things work, so normally it didn't have this and doesn't use it.

istream & operator>>(istream & _istream, PDBParser &rhs)
{
//      ifstream in;

//      _istream >> rhs.grabAtoms(in) >> rhs.findAtoms();

    _istream >> rhs.backupinfile;

    rhs.grabAtoms(rhs.backupinfile);
    rhs.findAtoms();

    return _istream;
}

I've established that the issue here is that my function needs to receive an ifstream object and I can't figure out how to get that from the istream object.

Here's my working << overload just for the heck of it:

ostream & operator<<(ostream & _ostream, PDBParser &rhs)
{
    for(int i=0; i < rhs.x1->getSize(); i++)
        {
            _ostream.precision(3);
            _ostream << fixed;
            _ostream << setprecision (3) << rhs.x1->get(i) << " ";
            _ostream << setprecision (3) << rhs.y1->get(i) << " ";
            _ostream << setprecision (3) << rhs.z1->get(i) << " ";
            _ostream << setprecision (3) << rhs.x2->get(i) << " ";
            _ostream << setprecision (3) << rhs.y2->get(i) << " ";
            _ostream << setprecision (3) << rhs.z2->get(i) << endl;
                    }
    return _ostream;
}

Thanks