Linking error: undefined reference to `vtable for XXX`

Question

There is some linking error here. I looked for that online, yet still I couldn't find the problem. How can I fix it?

g++ test.cpp -o test
/tmp/ccDfCj4N.o: In function `Interval::Interval()':
test.cpp:(.text._ZN8IntervalC2Ev[Interval::Interval()]+0x9): undefined reference to     `vtable for Interval'
/tmp/ccDfCj4N.o: In function `IntInterval::~IntInterval()':
test.cpp:(.text._ZN11IntIntervalD0Ev[IntInterval::~IntInterval()]+0x1d): undefined     reference to `Interval::~Interval()'
/tmp/ccDfCj4N.o: In function `IntInterval::~IntInterval()':
test.cpp:(.text._ZN11IntIntervalD1Ev[IntInterval::~IntInterval()]+0x1d): undefined     reference to `Interval::~Interval()'
/tmp/ccDfCj4N.o:(.rodata._ZTI11IntInterval[typeinfo for IntInterval]+0x10): undefined     reference to `typeinfo for Interval'
collect2: ld returned 1 exit status

Here is the code! All classes are in a same file for a pilot program.

#include <iostream>
#include <vector>
#include <utility>
using namespace std;

#define MAX_IP_RANGE    4294967295

class Interval {

    public:
        virtual Interval * interval_copy() = 0;
        virtual unsigned long get_begin() = 0;
        virtual unsigned long get_end() = 0;
        virtual unsigned long get_length() = 0;
        virtual Interval*     get_intersect(Interval *interval) = 0;   // Examine whether two intervals have intersection
        virtual Interval*     copy() = 0;
        virtual ~Interval();
        virtual bool is_equal(Interval *interval) {
            unsigned long b1 = this->get_begin();
            unsigned long e1 = this->get_end();
            unsigned long b2 = interval->get_begin();
            unsigned long e2 = interval->get_end();
            if (b1 == b2 && e1 == e2)
                    return true;
            return false;
        }

        virtual bool is_within(Interval *interval) {
            unsigned long b1 = this->get_begin();
            unsigned long e1 = this->get_end();
            unsigned long b2 = interval->get_begin();
            unsigned long e2 = interval->get_end();
            if (b1 >= b2 && e1 <= e2)
                return true;
            return false;
        }

        virtual bool contains(Interval *interval) {    // Examine whether this interval contains another interval
            unsigned long b1 = this->get_begin();
            unsigned long e1 = this->get_end();
            unsigned long b2 = interval->get_begin();
            unsigned long e2 = interval->get_end();
            if (b1 <= b2 && e1 >= e2)
                return true;
            return false;
        }

        virtual bool is_empty() {
            return (get_end()<get_begin())?true:false;
        }

        virtual bool is_intersect(Interval *interval) {
            unsigned long b1 = this->get_begin();
            unsigned long e1 = this->get_end();
            unsigned long b2 = interval->get_begin();
            unsigned long e2 = interval->get_end();

            if (b1>e2)
                return false;
            if (b2>e1)
                return false;
            return true;
        }

        virtual void print()
        {
            cout << '('<<get_begin() << ',' << get_end() << ")\n";
        }
};


class IntInterval : public Interval {
    private:
        unsigned long begin;
        unsigned long end;
        IntInterval();

    public:
        virtual Interval * interval_copy() {
            return new IntInterval(begin, end);
        }

        IntInterval(unsigned long a, unsigned long b): begin (a), end  (b)
        {}

        void set_value(unsigned long a, unsigned long b) {
            begin = a;
            end = b;
        }

        void set_begin(unsigned long a) {
            begin = a;
        }

        void set_end(unsigned long b) {
            end = b;
        }

        virtual Interval* copy()
        {
            Interval *new_interval = new IntInterval(begin, end);
            return new_interval;
        }

        virtual unsigned long get_begin() {
            return begin;
        }

        virtual unsigned long get_length() {
            return end-begin+1;
        }

        virtual unsigned long  get_end() {
            return end;
        }

        virtual Interval* get_intersect(Interval *interval);   // Get the intersect part of two intervals
        virtual ~IntInterval() {};
    };

    Interval* IntInterval::get_intersect(Interval *interval) {
        unsigned long begin2 = interval->get_begin();
        unsigned long end2 = interval->get_end();
        if (end < begin2 || begin > end2) {
            return new IntInterval(1, 0);
        }
        return new IntInterval((begin>begin2)?begin:begin2, (end<end2)?end:end2);
    }


    IntInterval * parse_ip(const char * _str) {
        unsigned long  _begin=0;
        unsigned long  _end=0;
        string input(_str);
        if (input.find('-') != string::npos){
            string begin = input.substr(0, input.find('-'));
            string end = input.substr(input.find('-')+1);

            unsigned  int ip1 = 0, ip2 = 0;
            unsigned  int ip3 = 0, ip4 = 0;
            sscanf(begin.c_str(), "%u.%u.%u.%u", &ip1, &ip2, &ip3, &ip4);
            _begin = (ip1 << 24) + (ip2 << 16) + (ip3 << 8) + ip4;

            ip1 = 0; ip2 = 0; ip3 = 0; ip4 = 0;
            sscanf(end.c_str(), "%u.%u.%u.%u", &ip1, &ip2, &ip3, &ip4);
            _end = (ip1 << 24) + (ip2 << 16) + (ip3 << 8) + ip4;

            if ((_begin > _end) ||  (_end > MAX_IP_RANGE)){
                cout<<"ERROR: The IP INTERVAL IS WRONG The range is "<<begin<<"-"<<end<<endl;
                exit(0);
            }
        }
        return new IntInterval(_begin, _end);
    }

    bool compFunc (Interval * i, Interval * j) {
        return (i->get_begin() < j->get_begin());
    }

    int main () {

        vector <vector<pair<string, string> > > nets;

        vector<pair<string, string> > x;
        vector<pair<string, string> > y;

        x.push_back(make_pair("1.1.1.1", "3.0.0.0"));
        x.push_back(make_pair("10.2.5.3", "30.2.5.0"));
        x.push_back(make_pair("100.2.25.2", "130.2.25.2"));

        y.push_back(make_pair("41.0.2.2", "43.2.2.5"));
        y.push_back(make_pair("131.2.2.2", "135.5.5.2"));

        nets.push_back(x);
        nets.push_back(y);

        vector <IntInterval *> _nets;
        for (int i=0; i<(int)nets.size(); i++)
            for(int j=0; j<(int)nets[i].size(); j++) {
                string s = nets[i][j].first + '-' + nets[i][j].second;
                _nets.push_back(parse_ip(s.c_str()));
            }
        sort(_nets.begin(), _nets.end(), compFunc);

        if (_nets.size()>1)
            for (vector<IntInterval *>::iterator it = _nets.begin()+1; it < _nets.end(); ) {
                if ((*it)->get_begin()-1 == (*(it-1))->get_end()) {
                    (*(it-1))->set_end((*it)->get_end());
                    _nets.erase(it);
                }
                else if ((*it)->get_begin()-1 <  (*(it-1))->get_end()) {
                    it++;
                    cout<<"ERROR: Network address overlapping!"<<endl;
                }
                else
                    it++;
            }

        for (int i=0; i<(int)_nets.size(); i++)
            cout << _nets[i]->get_begin() << "  " << _nets[i]->get_end() << endl;

      return 0;
    }

bdonlan · Accepted Answer · 2011-10-11T00:40:44.430

43

You never provided an implementation for virtual ~Interval(); and several other functions. You must provide an implementation for all non-pure virtual functions you declare. In particular, G++ emits the vtable along with the implementation of the first-declared non-inline function in a class. Omitting its implementation means you won't have a vtable, and thus won't be able to construct the class (hence these errors).

In short, define every function you declare, except for pure virtuals. There are some cases where it's justified to leave out the definition for a declared function, but they are very rare.

edited Oct 11 '11 at 00:40

answered Oct 11 '11 at 00:35

bdonlan

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1

But the linker error is coming from default constructor `Interval::Interval()` as well. Why is that ? – Mahesh Oct 11 '11 at 00:37
6

Right, because it is the constructor that needs all the methods to be implemented in order to build the vtable. – Raymond Chen Oct 11 '11 at 00:39
2

aaah.. you are right... I just added Interval::~Interval(){} and it worked! – Amir Oct 11 '11 at 00:39

score 2 · Answer 2 · answered Nov 13 '12 at 22:19

I had the same problem. I was merging my code with upstream changes and picked my change over another engineer's seemingly identical change in the header file. It just turned out that they had changed the constness of the method and I hadn't noticed, and you will get this error for the reason @bdonian says.

virtual void foo(Many params, As part, Of veryLong, Method signature);

and theirs:

virtual void foo(Many params, As part, Of veryLong, Method signature) const;

When merging I picked the first version, but the implementation had the second one, resulting in the compiler assuming there is an overload of foo() that is undefined, and hence the error.

score -3 · Answer 3 · edited Jun 26 '16 at 10:25

-3

In virtual classes never put undefined functions first. Move

IntInterval();

to after the first defined function:

private:
    unsigned long begin;
    unsigned long end;

public:
    virtual Interval * interval_copy(){return new IntInterval(begin,end);}
    IntInterval(unsigned long a,unsigned long b): begin (a),
                                  end  (b)
    {}
private:
    IntInterval();
public:

It's because C++ glues the vtable to the first function. If you don't define it, the vtable will be undefined as well.

As mentioned by other answers, you need to also define the destructor:

public:
    virtual ~IntInterval()
    {
        // Destruction code
    }

edited Jun 26 '16 at 10:25

Peter Mortensen

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answered Oct 11 '11 at 00:34

Daniel

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This won't fix anything. You still need to define the functions you declare. He's missing definitions for several virtual functions, so even if you managed to get G++ to emit a vtable, the vtable itself will cause more link errors for the undefined virtuals. – bdonlan Oct 11 '11 at 00:36
@bdonlan: this will make the `undefined vtable for` to go away. he doesn't need to define functions he doesn't use. – Daniel Oct 11 '11 at 00:37
yes, and it would be replaced with `undefined reference to Interval::~Interval`. Better to define the functions, or remove them if he doesn't need them! – bdonlan Oct 11 '11 at 00:38
@bdonlan: `Interval::~Interval` is not `Interval::Interval`. he probably done undefined private default constructor so it cannot be used, e.g. `Interval a;` won't work, while `Interval a(1,2)` will. – Daniel Oct 11 '11 at 00:40
Re "Its because c++ glues the vtable to the first function" - no, C++ doesn't specify when or where the vtable is generated, or even whether virtual dispatch is implemented using a vtable at all. You are describing the behaviour of one particular compiler; other compilers may behave differently, so playing games with declaration order to mask the error is not portable. – Mike Seymour Oct 11 '11 at 10:56
@MikeSeymour: but thats what all compilers I know do. try to make a virtual class with first function undeclared and see what happens. – Daniel Oct 11 '11 at 15:28
@Dani: I'm well aware that at least some compilers do what you describe. But this problem should be fixed properly (by defining everything that needs defining), not bodged until it happens to work on whichever compiler you're using. – Mike Seymour Oct 11 '11 at 15:36
@MikeSeymour: its completely within the c++ standard to have an undefined function. its most the c++ compilers violate the standard by not allowing an undefined function to come first. if you have a compiler that violates the standard, you have to bodge the code to work. – Daniel Oct 11 '11 at 15:40
@Dani: No, you must define all non-pure virtual functions. C++11 10.3/11: "A virtual function declared in a class shall be defined, or declared pure in that class, or both" – Mike Seymour Oct 11 '11 at 15:45

Linking error: undefined reference to `vtable for XXX`

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