call member function without object-compile error

Dear c++ advancer:
  I have a simple c++ file, which is I copy and try to test from a
book (C++ Primer 3rd Ed, by Stanley B. Lippman and Josee Lajoie,
around page 904, chapter 17.3 Base Class Member Access)
the following is my program:
------------------------------------------
#include <iostream>
#include <vector>
#include <set>
#include <string>
#include <utility>
#include <map>

using namespace std;

typedef pair< short, short > location;

class Query {
public:
    // constructors and destructor
    // are discussed in Section 17.4

   // copy constructor and copy assignment operator
    // are discussed in Section 17.6

    // operations supporting public interface
    virtual void eval() = 0;
    void display () const;

    // read access functions
    const set<short> *solution() const;
    const vector<location> *locations() const { return &_loc; }

protected:
    Query();
    set<short> *_vec2set( const vector<location>* );

    static vector<string> *_text_file;

    set<short> *_solution;
    vector<location> _loc;

private:
    explicit Query( const vector<location>& );
};

/*
inline const set<short>*
Query::
solution()
{
  return _solution
        ? _solution
        : _solution = _vec2set( &_loc );
}
*/

typedef vector<location> loc;

inline
Query::
Query( const vector< location > &loc )
     : _solution( 0 ), _loc( loc )
{}

class NameQuery : public Query {
public:
    // ...

    // overrides virtual Query::eval() instance
    void eval();

    // read access function
    string name() const { return _name; }

    static const map<string,loc*> *word_map() { return _word_map; }
    bool compare0(const Query *);
 protected:
     string _name;
     static map<string,loc*> *_word_map;
};

bool
NameQuery::
compare0( const Query *pquery )
{
    // ok: protected member of its Query subobject
    int myMatches = _loc.size();

    // error: has no direct access rights to the
    // protected member of an independent query object
    int itsMatches = pquery->_loc.size();

    return myMatches == itsMatches;
}

int main() {
  bool aa;
  const Query *p1;
  aa = NameQuery::compare0(p1);

  return 0;
}
-----------------------------
the following is my g++ result(4.5.2)
--------------------
eric@eric-laptop:~/CppPrimer3$ g++ p904.cpp
p904.cpp: In member function =91bool NameQuery::compare0(const Query*)':
p904.cpp:36:24: error: =91std::vector<std::pair<short int, short int> >
Query::_loc' is protected
p904.cpp:88:30: error: within this context
p904.cpp: In function =91int main()':
p904.cpp:96:30: error: cannot call member function =91bool
NameQuery::compare0(const Query*)' without object
eric@eric-laptop:~/CppPrimer3$
--------------------------------------
I just like to know how to fix (88:30) and (96:30)
thanks a lot in advance, Eric