undefined reference to vtable when using interface - c++

Question

I've looked around, and I can't quite figure out where I'm going wrong, as I seem to be following the correct convention when using interfaces, but perhaps I'm overlooking something. The exact error I'm getting is:
undefined reference to `vtable for Icommand'
I've only just begun to seperate my classes and class declarations into separate header files, so perhaps I'm missing a preprocessor directive somewhere.
main.cpp:
#include <iostream>
#include <string>
#include <cstdlib>
#include "Icommand.h"
#include "Command.h"
using namespace std;
void pause();
int main(){
Icommand *run = new Command("TEST");
cout << run->getCommand() << endl;
delete run;
pause();
}
void pause(){
cin.clear();
cin.ignore(cin.rdbuf()->in_avail());
cin.get();
}
Icommand.h:
#ifndef ICOMMAND_H
#define ICOMMAND_H
#include <string>
#include <vector>
class Icommand
{
private:
public:
Icommand(){}
virtual ~Icommand(){}
virtual bool run(std::string object1) = 0;
virtual bool run(std::string object1, std::string object2) = 0;
virtual std::string getCommand() const;
};
#endif // ICOMMAND_H
Command.h:
#ifndef COMMAND_H
#define COMMAND_H
#include <string>
#include <vector>
#include "Icommand.h"
class Command : public Icommand {
private:
std::string command;
std::vector<std::string> synonymns;
Command(); // private so class much be instantiated with a command
public:
Command(std::string command) : command(command){}
~Command(){}
bool run(std::string object1);
bool run(std::string object1, std::string object2);
std::string getCommand() const;
};
#endif // COMMAND_H
Command.cpp:
#include <string>
#include <vector>
#include "Command.h"
bool Command::run(std::string object1){
return false;
}
bool Command::run(std::string object1, std::string object2){
return false;
}
std::string Command::getCommand() const {return command;}

Answer 1

In Icommand.h, replace
virtual std::string getCommand() const;
with
virtual std::string getCommand() const = 0;
to make it pure virtual. Then the compiler can generate a vtable for Icommand. Alternatively, implement Icommand::getCommand.