undefined reference to `vtable for Player'

Question

I've looked at a lot of other similar questions but none of them have seemed to help. I've used virtual functions before but this time they just don't seem to be working.

Header for parent class:

#ifndef OBJECT_OBJECT
#define OBJECT_OBJECT
#include <raylib.h>
#include <raymath.h>

class Object {
public:
    Object() {}
    Object(Rectangle rect, Color color);
    Object(int x, int y, int width, int height, Color color);
    virtual void Update(float deltaTime) {}
    Rectangle rect;
    Color color;
};

#endif /* OBJECT_OBJECT */

Source for parent class:

#include "Object.hpp"

Object::Object(Rectangle rect, Color color) {
    this->rect = rect;
    this->color = color;
}

Object::Object(int x, int y, int width, int height, Color color) {
    this->rect = { (float)x, (float)y, (float)width, (float)height };
    this->color = color;
}

Header for child:

#ifndef OBJECT_OBJECTS_PLAYER
#define OBJECT_OBJECTS_PLAYER
#include <stdio.h>
#include "../Object.hpp"

class Player : public Object {
public:
    Player() {}
    Player(Rectangle rect, Color color) : Object(rect, color) {}
    Player(int x, int y, int width, int height, Color color) : Object(x, y, width, height, color) {}
    void Update(float deltaTime) override;
    int speed = 10;
};

#endif /* OBJECT_OBJECTS_PLAYER */

Source for child:

#include "Player.hpp"

void Player::Update(float deltaTime) {
    if (IsKeyPressed(KEY_W | KEY_UP)) this->rect.y -= speed * deltaTime;
    if (IsKeyPressed(KEY_S | KEY_DOWN)) this->rect.y += speed * deltaTime;
    if (IsKeyPressed(KEY_A | KEY_LEFT)) this->rect.x -= speed * deltaTime;
    if (IsKeyPressed(KEY_D | KEY_RIGHT)) this->rect.x += speed * deltaTime;
}

Full main.cpp file:

#include <raylib.h>
#include <raymath.h>
#include <vector>
#include <string>
#include "Object/Object.hpp"
#include "Object/Objects/Player.hpp"

void NewObject(Rectangle rect, Color color);
void NewObject(Object obj);
std::vector<Object> objects;
bool shouldClose;
int screenWidth;
int screenHeight;

int main(void) {
    InitWindow(0, 0, "2D Platformer");
    screenWidth = GetScreenWidth();
    screenHeight = GetScreenHeight();
    SetExitKey(-1);
    ToggleFullscreen();

    Player player({ 0, 0, 20, 20 }, (Color){0, 255, 0, 255});
    NewObject(player);

    Camera2D camera = { 0 };
    camera.target = (Vector2){0, 0};
    camera.offset = (Vector2){ screenWidth/2.0f, screenHeight/2.0f };
    camera.rotation = 0.0f;
    camera.zoom = 1.0f;

    while (!WindowShouldClose()) {
        float deltaTime = GetFrameTime();
        BeginDrawing();

            ClearBackground(RAYWHITE);
            
            BeginMode2D(camera);

                for (int i = 0; i < objects.size(); i++) {
                    objects[i].Update(deltaTime);
                    DrawRectangleRec(objects[i].rect, objects[i].color);
                }

            EndMode2D();

        EndDrawing();
    }
    CloseWindow();

    return 0;
}

void NewObject(Rectangle rect, Color color) {
    objects.push_back(*(new Object(rect, color)));
}

void NewObject(Object obj) {
    objects.push_back(obj);
}

CMakeLists.txt files:

cmake_minimum_required(VERSION 3.11)
project(safcal)
cmake_policy(SET CMP0076 NEW)
find_package(raylib 3.0 QUIET)

if (NOT raylib_FOUND)
  include(FetchContent)

  FetchContent_Declare(
    raylib
    URL https://github.com/raysan5/raylib/archive/master.tar.gz
  )

  FetchContent_GetProperties(raylib)
  if (NOT raylib_POPULATED)
    set(FETCHCONTENT_QUIET NO)
    FetchContent_Populate(raylib)

    set(BUILD_EXAMPLES OFF CACHE BOOL "" FORCE)
    add_subdirectory(${raylib_SOURCE_DIR} ${raylib_BINARY_DIR})

  endif()

endif()
add_executable(${PROJECT_NAME})
target_sources(${PROJECT_NAME} PRIVATE main.cpp)
add_subdirectory(Object)
target_link_libraries(${PROJECT_NAME} raylib)


target_sources(${PROJECT_NAME} PRIVATE 
    "Object.cpp"
)


target_sources(safcal PRIVATE 
    "Player.cpp"
)

The problem is with the Update function. Commenting anything to do with it being overridden stops the error.

EDIT: The full error

[build] FAILED: safcal 
[build] : && /bin/x86_64-linux-gnu-g++-10 -g  CMakeFiles/safcal.dir/main.cpp.o CMakeFiles/safcal.dir/Object/Object.cpp.o -o safcal  _deps/raylib-build/raylib/libraylib.a  -lm  -lpthread  /usr/lib/x86_64-linux-gnu/libGL.so  /usr/lib/x86_64-linux-gnu/libGLU.so  _deps/raylib-build/raylib/external/glfw/src/libglfw3.a  -lpthread  /usr/lib/x86_64-linux-gnu/librt.so  -lm  -ldl && :
[build] /usr/bin/ld: CMakeFiles/safcal.dir/main.cpp.o: warning: relocation against `_ZTV6Player' in read-only section `.text._ZN6PlayerC2E9Rectangle5Color[_ZN6PlayerC5E9Rectangle5Color]'
[build] /usr/bin/ld: CMakeFiles/safcal.dir/main.cpp.o: in function `Player::Player(Rectangle, Color)':
[build] /home/callum/Documents/Programming/C++/SafCal/build/../Object/Objects/Player.hpp:9: undefined reference to `vtable for Player'
[build] /usr/bin/ld: warning: creating DT_TEXTREL in a PIE

But seems the most mundane and usual issue that you do not link the "source for child" to your program. — Öö Tiib, Dec 08 '21 at 01:20
ive added it in the cmakelists.txt using target_sources. is this good enough? — Callum Tomkins, Dec 08 '21 at 01:22
Drop a `virtual` destructor into `Object` and see if magic happens. — user4581301, Dec 08 '21 at 01:35
@user4581301 adding that seems to have caused more problems [build] /usr/bin/ld: CMakeFiles/safcal.dir/main.cpp.o: in function `Player::Player(Rectangle, Color)': [build] /home/callum/Documents/Programming/C++/SafCal/build/../Object/Objects/Player.hpp:9: undefined reference to `vtable for Player' [build] /usr/bin/ld: CMakeFiles/safcal.dir/main.cpp.o: in function `Player::~Player()': [build] /home/callum/Documents/Programming/C++/SafCal/build/../Object/Objects/Player.hpp:6: undefined reference to `vtable for Player' — Callum Tomkins, Dec 08 '21 at 01:40
Your cmakelist.txt is probably something unusual as target_sources() is typically used for ease of handling and deployment of sub-libraries. — Öö Tiib, Dec 08 '21 at 01:47
id like to be able to do it in the seperate cmakelists files in each sub folder can that be done with add_executable? — Callum Tomkins, Dec 08 '21 at 01:53
Minimum reproducible example: https://godbolt.org/z/jeGeqWveo — paddy, Dec 08 '21 at 01:55
You'd like but have apparently failed something in your undisclosed cmakelist.txt files. — Öö Tiib, Dec 08 '21 at 02:01
Interesting, but I'd keep the destructors. You'll need them. — user4581301, Dec 08 '21 at 02:47

score 0 · Answer 1 · answered Dec 08 '21 at 03:20

I've used virtual functions before but this time they just don't seem to be working.

Object slicing occurred in your code， So you can't see the desired result。

Player player({ 0, 0, 20, 20 }, (Color){0, 255, 0, 255});
NewObject(player);

You can try to make the following changes:

std::vector<std::shared_ptr<Object>> objects;

...

void NewObject(std::shared_ptr<Object> obj) {
    objects.push_back(obj);
}

...

NewObject(new Player());

In addition, the destructor of the base class needs to be declared as a virtual function。

undefined reference to `vtable for Player'

1 Answers1