Re: call member function without object-compile error

eric <>
Tue, 21 Jun 2011 21:36:55 -0700 (PDT)
On Jun 21, 8:55 pm, Ian Collins <> wrote:

On 06/22/11 03:28 PM, eric wrote:

On Jun 21, 8:12 pm, Ian Collins<> wrote:

On 06/22/11 03:01 PM, eric wrote:

Dear c++ advancer:
    I have a simple c++ file, which is I copy and try to test fro=

m 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:

<snip for brevity>

the following is my g++ result(4.5.2)
eric@eric-laptop:~/CppPrimer3$ g++ p904.cpp
p904.cpp: In member function bool NameQuery::compare0(const Query*) :
p904.cpp:36:24: error: std::vector<std::pair<short int, short int> =


Query::_loc is protected
p904.cpp:88:30: error: within this context
p904.cpp: In function int main() :
p904.cpp:96:30: error: cannot call member function bool
NameQuery::compare0(const Query*) without object
I just like to know how to fix (88:30) and (96:30)
thanks a lot in advance, Eric

For the protected access, provide a public member function to return t=


vector size.

For the call, you have to have an instance of NameQuery to call a
non-static member function.

As a general point, names starting with leading underscores may clash
with names used by your implementation.

Thanks your reply and suggestion
but after I change leading underscore to a_ (add an "a" in front of
all _variablename)
my g++ still response name error : Cann't call memeber function
without object on (88:30 and 96:30) /* try by yourself */
still need any advancer's help and suggestion and thanks a lot in
advance, Eric

What about the other two suggestion to fix your actual problem?

Ian Collins

this is newest file I fix/modify with your suggestion
#include <iostream>
#include <vector>
#include <set>
#include <string>
#include <utility>
#include <map>

using namespace std;

typedef pair< short, short > location;

class Query {
    // 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 &a_loc; }
    int f_b() { return a_loc.size(); }

    set<short> *a_vec2set( const vector<location>* );

    static vector<string> *a_text_file;

    set<short> *a_solution;
    vector<location> a_loc;

    explicit Query( const vector<location>& );

inline const set<short>*
  return _solution
        ? _solution
        : _solution = _vec2set( &_loc );

typedef vector<location> loc;

Query( const vector< location > &loc )
     : a_solution( 0 ), a_loc( loc )

class NameQuery : public Query {
    // ...

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

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

    static const map<string,loc*> *word_map() { return a_word_map; }
    bool compare0( Query *pquery);
     string a_name;
     static map<string,loc*> *a_word_map;

compare0( Query *pquery )
    // ok: protected member of its Query subobject
    int myMatches = a_loc.size();

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

    return myMatches == itsMatches;

int main() {
  bool aa;
  Query *p1;
  NameQuery d;
  aa = d.compare0(p1);

  return 0;
my g++ reponse linker error
eric@eric-laptop:~/CppPrimer3$ g++ p904.cpp
/tmp/ccBLCYgi.o: In function `NameQuery::NameQuery()':
p904.cpp:(.text._ZN9NameQueryC2Ev[_ZN9NameQueryC5Ev]+0xe): undefined
reference to `Query::Query()'
p904.cpp:(.text._ZN9NameQueryC2Ev[_ZN9NameQueryC5Ev]+0x17): undefined
reference to `vtable for NameQuery'
/tmp/ccBLCYgi.o: In function `NameQuery::~NameQuery()':
p904.cpp:(.text._ZN9NameQueryD2Ev[_ZN9NameQueryD5Ev]+0xc): undefined
reference to `vtable for NameQuery'
collect2: ld returned 1 exit status
Need any advancer's suggestion and help again, and thanks a lot in
advance, Eric

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