Undefined reference to a virtual function [duplicate] - c++

Question

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Virtual/pure virtual explained
(12 answers)
Closed 1 year ago.
booking.h
#ifndef _BOOKING_H_
#define _BOOKING_H_
#include <string>
class Event {
private:
std::string event_option;
public:
Event(std::string event_option);
virtual ~Event();
void list_specific_event_details();
virtual void list_details();
};
class Films : public Event {
private:
std::string movie_option;
public:
Films(std::string movie_option);
void list_details();
};
class Live_Music : public Event {
private:
std::string live_music_option;
public:
Live_Music(std::string live_music_option);
void list_details();
};
class Standup_Comedy : public Event {
private:
std::string comedy_option;
public:
Standup_Comedy(std::string comedy_option);
void list_details();
};
#endif
booking.cpp
#include "booking.h"
#include <string>
Event::Event(std::string event_option)
{
this->event_option = event_option;
}
Event::~Event()
{
}
void Event::list_specific_event_details()
{
return list_details();
}
Films::Films(std::string movie_option) : Event("Films")
{
this->movie_option = movie_option;
}
void Films::list_details()
{
//some code ...
return;
}
Live_Music::Live_Music(std::string live_music_option) : Event("Live_Music")
{
this->live_music_option = live_music_option;
}
void Live_Music::list_details()
{
//some code...
return;
}
Standup_Comedy::Standup_Comedy(std::string comedy_option) : Event("Standup_Comedy")
{
this->comedy_option = comedy_option;
}
void Standup_Comedy::list_details()
{
//some code...
return;
}
main.cpp
#include "booking.h"
#include <iostream>
#include <vector>
#include <string>
int main()
{
std::vector <Event *> choice;
choice.push_back(new Films("f"));
choice.push_back(new Live_Music("l"));
choice.push_back(new Standup_Comedy("s"));
for(unsigned i = 0; i < choice.size(); i++)
{
choice[i] -> list_specific_event_details();
}
for (Event * e: choice) delete e;
choice.clear();
}
I have written the above block of codes and got an error when I tried to compile it.
The error is as follows:
usr/lib/gcc/x86_64-pc-cygwin/11/../../../../x86_64-pc-cygwin/bin/ld: /tmp/ccuWXzBM.o:booking.cpp:(.rdata$_ZTV5Event[_ZTV5Event]+0x20): undefined reference to `Event::list_details()'
collect2: error: ld returned 1 exit status
Why am I getting this error, and how can I solve it?

Answer 1

You have not defined your method Event::list_details(). If you only want to declare the function but do not want to implement it, that is what is called an Interface, you can make it a pure virtual method with:
class Event
{
...
virtual void list_details() = 0;
...
};