virtual function declaration in header [duplicate] - c++

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;
}

Answer 1

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.

Answer 2

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.

Answer 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
}