Undefined reference to 'vtable for xxx' - c++

Question

takeaway.o: In function `takeaway':
project:145: undefined reference to `vtable for takeaway'
project:145: undefined reference to `vtable for takeaway'
takeaway.o: In function `~takeaway':
project:151: undefined reference to `vtable for takeaway'
project:151: undefined reference to `vtable for takeaway'
takeaway.o: In function `gameCore':
project.h:109: undefined reference to `gameCore<int>::initialData(int)'
collect2: ld returned 1 exit status
make: *** [takeaway] Error 1
I keep getting this Error from the linker , i know it has something to do with inline functions getting a vtable temporarily stored. But what that entails i am not quite sure. I would assume it has something to do with how i call gameCore's constructor in the initilization list of takeaway.cpp
I have a templated class (gameCore.h)
and a class (takeaway.cpp) that is inheriting from gameCore
The vtable error is called 3 times
1)in takeaways constructor
2) takeaways destructor
3)in gameCores constructor
I am using G++
Here is the code:
(i know it may seem hard to read but i have marked off exatcly where the erros occur)
takeaway.h
#ifndef _TAKEAWAY_H_
#define _TAKEAWAY_H_
#include<map>
#include<cctype>
#include<stack>
#include<map>
#include<iostream>
#include<string>
#include<cstdlib>
#include"gameCore.h"
#include<vector>
using namespace std;
class takeaway : public gameCore<int>
{
private:
public:
// template<class Penny>
void textualGame();
bool isNum(string str);
// template<class Penny>
stack<int> initialData(int initial);
// template<class Position>
int score (int position);
// template<class Position>
stack<int> addStack(int currentPos, stack<int> possiblePositions);
// template<class Penny>
takeaway (int initial);
// template<class Position>
~takeaway();
};
bool isNum(string str);
int charToint(char *theChar);
#endif
takeaway.cpp
/*
Description :
This game communicates with the gameCore class to determine the results
of a game of takeaway played between two computers or a computer and human.
*/
#include "takeaway.h"
/*
Description:Creates a stack represening initial data
Note:Change to a vector eventually
return : stack of int
*/
stack<int> takeaway:: initialData(int initial){
stack<int> returnStack;
int theScore = score(initial);
int final;
if(initial ==0)
{
final = 1;
}
else
{
final = 0;
}
returnStack.push(theScore);
returnStack.push(final);
return returnStack;
}
/*
Description: a textual representation of the game
Note: This is still terribly wrong
*/
void textualGame(){
cout <<"this is the best i could do for a graphical representation";
}
/*
Description: Deetermines if a number is even
Note: Helper function for determining win or loss positions
Returns: 1 if it is and 0 if it is not
*/
int takeaway::score(int position){
if(position % 2 == 0)
{
return 1;
}
return 0;
}
/*
Description: Will return a stack , withouth the given postion in it
will contain all positions possible after the given position
along with anyother that wehre in the given stack.This function
Must also update the map to represent updated positions
Takes: a position to check and a stack to return
Returns: A stack of possible positions.
*/
stack<int> takeaway::addStack(int currentPos, stack<int> possiblePositions ){
if(currentPos != 0)
{
// If even
if( currentPos % 2 == 0)
{
// Create a data aray with score of the new positon and mark it as not final
int data[] = {score(currentPos/2),0};
vector<int> theData(data, data+sizeof(data));
int pos = currentPos/2;
// Add it to the map
//this -> gamesMap[currentPos/2] = dataArray;
this -> gamesMap.insert(std::pair<int, vector<int> >(pos, theData));
// Add it to the possible positions
possiblePositions.push(pos);
}
if(currentPos % 3 == 0)
{
int data[] = {score(currentPos/3),0};
vector<int> theData(data,data+sizeof(data));
int pos = currentPos/3;
//this -> gamesMap[currentPos/3] = dataArray;
this -> gamesMap.insert(std::pair<int, vector<int> >(pos, theData));
possiblePositions.push(pos);
}
// Work for the position that represents taking one penny
int minusFinal = 0;
if(currentPos - 1 == 0)
{
minusFinal = 1;
}
int data[] = {score(currentPos - 1),minusFinal};
vector<int> theData(data,data+sizeof(data));
int pos = currentPos - 1;
// this -> gamesMap[currentPos -1] = dataArary
this->gamesMap.insert(std::pair<int,vector<int> >(pos, theData));
possiblePositions.push(pos);
}
return possiblePositions;
}
/*
Description: Constructor for the takeaway game
OA takes: a initial position, and initial data for it
*/
takeaway::takeaway(int initial):gameCore<int>::gameCore(initial){ //<--- ERROR HERE
//Constructor
}
/*
Description: Destuctor
*/
takeaway::~takeaway(){ // <--------------------- ERROR HERE
//Destructor
}
//checks input and creates game.
int main(int argc, char* argv[]){
int numberPennies ;
string game = argv[0];
if(argc == 2 && isNum(argv[1]) )
{
int pennies = charToint(argv[1]);
takeaway gameInstance(pennies ); // Creates a instance of $
}
// else if(argc == 3 && argv[1] == "play" && isNum(argv[2]) )
// {
// int pennies = charToint(argv[2]);
// takeaway<int> gameInstance(pennies); // Craete a human playab$
// }
else
{
cerr << "Error->Usage: " << game <<" [play] numberOfPennies \n";
exit (1);
}
return 0;
}
//Converts a char to a integer
int charToint(char *theChar){
int theInt = atoi(theChar);
return theInt;
}
//Determines if a string is numeric
bool isNum(string str){
for(int i = 0;i < str.length() ;i++){
if(isdigit(str[i]) != 1)
{
cerr << "Error->Input: Number must be a Positive Integer the charecter '" << str[i]<< "' invalidated your input. \n" ;
exit(1);
return false;
}
}
return true;
}
gameCore.h
/*
gameCore.h
Description:
This class created gameMap that are written as a template
They will communicate with the specific game and the algorithm
To keep track of positions ans there values.
*/
#ifndef GAMECORE_H
#define GAMECORE_H
#include <map>
#include <stack>
#include <string>
#include <vector>
using namespace std;
template <class Position>
class gameCore
{
protected:
//Best Move used by algorithim
Position bestMove;
//The current highest score used by the algorithim
int highestScore ;
//Stack to be used to remmeber what move created the score
stack<Position> movedFrom;
//Stack used for the algorithim.
stack<Position> curWorkingPos;
//The actual Map that the data will be held in.
map<Position,vector<int> > gamesMap;
public:
/*
Description : finds the data array for a poisition
takes: a Position
Returns: a array of integers /**
*/
virtual stack<int> initialData(Position pos) = 0;
/*
Description: Game must implement a way to determine a positions
score.
*/
virtual int score(Position pos) = 0;
/*
Description: A Graphical representation of the game
*/
virtual void textualGame() = 0;
/*
Description: a virtual function implemented by the child class
it will return a stack without the given position in it.This stack
will contain all positions available from the given postion as well as
all position already in the given stack. Also it will update the map with
all generated positions.
TAkes: a postion to check and a stack of currently working positons.
*/
virtual stack<Position> addStack(Position currentPos, stack<Position> possiblePositions ) = 0;
/*
Description:Constructor that
Creates a Map with positions as the key.
And an array of two integers that represent the positions
value and if we have moved here in the past.
Takes: a Initial Position and a Array of integers
*/
gameCore(Position initial){ // <-----ERROR HERE
//Determine the initial data and add it to the map and queue.
stack<int> theData = initialData(initial);
int first = theData.top();
theData.pop();
int second = theData.top();
theData.pop();
int initialData[] = {first,second};
vector<int> posData(initialData,initialData+sizeof(initialData));
gamesMap[initial] = posData;
curWorkingPos.push(initial);
}
/*
Description:
A destructor for the class
*/
~gameCore(){
//I do nothing but , this class needs a destructor
}
/*
Description: Takes the current position and returns
that positions Score.
Takes: A position
Returns:A integer that is a positions score.
*/
int getPosScore(Position thePos) const {
return this ->gamesMap.find(thePos)->second[0];
}
/*
Description: Adds values to a stack based on the current position
Takes: a poistion
*/
void updateStack(Position curPos){
this ->curWorkingPos =addStack(curPos,this ->curWorkingPos ); // get a stack from the game
// The game has a function that takes a position and a stack and based on the positions returns a stack identical to the last but with added values that represent valid moves from the postion./
}
/*
Description : Takes a positions and returns a integer
that depends on if the position is a final pos or not
Takes: A position
Returns: A Bool that represents if the position is a final(1) or not (0).
*/
// Possible change
bool isFinal(Position thePos) {
typename map<Position,vector<int> >::iterator iter = this ->gamesMap.find(thePos);
return iter->second[1] == 1 ;
}
/*
Description: Based on the given position determine if a move needs to be made.
(if not this is a end game position and it will return itself) If a move needs
to be made it will return the position to move to that is ideal.
Note: (because all positions can be represented as integers for any game , the return
type is a integer)
*/
int evaluatePosition(Position possiblePosition ){
if(isFinal(possiblePosition)) //If this is a final position
{
return getPosScore(possiblePosition); //Return the score
}
else
{
updateStack(possiblePosition); //Put all possible positions from this in thte stack
while(this -> curWorkingPos.size() != 0)
{
this -> movedFrom.push(this->curWorkingPos.front()); //take the top of the possible positions stack and set it the the moved from stack
this -> curWorkingPos.pop();
int curScore = evaluatePosition(this ->movedFrom.top()); //Recursive call for school
curScore = curScore * -1; //Negate the score
if(curScore > this -> highestScore) // if the score resulting from this position is biggest seen
{
highestScore = curScore;
this ->movedFrom.pop(); //do this first to get rid of the the lowest point
this -> bestMove = this ->movedFrom.top(); // mark where the lowest point came from
}
else
{
this -> movedFrom.pop();
}
}
}
return this -> bestMove;
}
//A Structure to determine if a position has a lower value than the second
struct posCompare{
bool operator() (Position pos1,Position pos2) const {
return (pos1.getPosScore() < pos2.getPosScore());
}
};
};
#endif

Answer 1

One or more of your .cpp files is not being linked in, or some non-inline functions in some class are not defined. In particular, takeaway::textualGame()'s implementation can't be found. Note that you've defined a textualGame() at toplevel, but this is distinct from a takeaway::textualGame() implementation - probably you just forgot the takeaway:: there.
What the error means is that the linker can't find the "vtable" for a class - every class with virtual functions has a "vtable" data structure associated with it. In GCC, this vtable is generated in the same .cpp file as the first listed non-inline member of the class; if there's no non-inline members, it will be generated wherever you instantiate the class, I believe. So you're probably failing to link the .cpp file with that first-listed non-inline member, or never defining that member in the first place.

Answer 2

The first set of errors, for the missing vtable, are caused because you do not implement takeaway::textualGame(); instead you implement a non-member function, textualGame(). I think that adding the missing takeaway:: will fix that.
The cause of the last error is that you're calling a virtual function, initialData(), from the constructor of gameCore. At this stage, virtual functions are dispatched according to the type currently being constructed (gameCore), not the most derived class (takeaway). This particular function is pure virtual, and so calling it here gives undefined behaviour.
Two possible solutions:
Move the initialisation code for gameCore out of the constructor and into a separate initialisation function, which must be called after the object is fully constructed; or
Separate gameCore into two classes: an abstract interface to be implemented by takeaway, and a concrete class containing the state. Construct takeaway first, and then pass it (via a reference to the interface class) to the constructor of the concrete class.
I would recommend the second, as it is a move towards smaller classes and looser coupling, and it will be harder to use the classes incorrectly. The first is more error-prone, as there is no way be sure that the initialisation function is called correctly.
One final point: the destructor of a base class should usually either be virtual (to allow polymorphic deletion) or protected (to prevent invalid polymorphic deletion).

Answer 3

If a class defines virtual methods outside that class, then g++ generates the vtable only in the object file that contains the outside-of-class definition of the virtual method that was declared first:
//test.h
struct str
{
virtual void f();
virtual void g();
};
//test1.cpp
#include "test.h"
void str::f(){}
//test2.cpp
#include "test.h"
void str::g(){}
The vtable will be in test1.o, but not in test2.o
This is an optimisation g++ implements to avoid having to compile in-class-defined virtual methods that would get pulled in by the vtable.
The link error you describe suggests that the definition of a virtual method (str::f in the example above) is missing in your project.

Answer 4

You may take a look at this answer to an identical question (as I understand):
https://stackoverflow.com/a/1478553
The link posted there explains the problem.
For quick solving your problem you should try to code something like this:
ImplementingClass::virtualFunctionToImplement(){...}
It helped me a lot.

Answer 5

Missing implementation of a function in class
The reason I faced this issue was because I had deleted the function's implementation from the cpp file, but forgotten to delete the declaration from the .h file.
My answer doesn't specifically answer your question, but lets people who come to this thread looking for answer know that this can also one cause.

Answer 6

it suggests that you fail to link the explicitly instantiated basetype public gameCore (whereas the header file forward declares it).
Since we know nothing about your build config/library dependencies, we can't really tell which link flags/source files are missing, but I hope the hint alone helps you fix ti.

Answer 7

GNU linker, in my case companion of GCC 8.1.0, well detects not re-declared pure virtual methods, but above certain complexity of class design it fails to identify missing implementation of methods and answers with a flat "V-Table Missing",
or even tends to report missing implementation, in spite it is there.
The only solution then is to verify consistency of declaration of implementation manually, method by method.

Answer 8

if you have virutal deconstruct function, you need to write it like this: ~SubListener() override = default; , don't forget this =default