main.cpp:(.text+0x5f): undefined reference to

Question

I try to compile some exercise from a SDL guide.

I compile like this:

g++ -o main main.cpp -I/usr/local/include/SDL2 -L/usr/local/lib -lSDL2

and i get this:

/tmp/cci2rYNF.o: In function `main':
main.cpp:(.text+0x5f): undefined reference to `Game::init(char const*, int, int, int, int, int)'
collect2: error: ld returned 1 exit status

and my code is:

main.cpp

#include "Game.h"

// our Game object
Game* g_game = 0;

int main(int argc, char* argv[])
{
    g_game = new Game();
    g_game->init("Chapter 1", 100, 100, 640, 480, 0);

    while(g_game->running())
    {
    g_game->handleEvents();
    g_game->update();
    g_game->render();
    }
    g_game->clean();

    return 0;
}

Game.h

#ifndef __Game__
#define __Game__

#include <SDL.h>

class Game
{
    public:
      Game() {}
      ~Game() {}

      bool init(const char* title, int xpos, int ypos, int width, int height, int flags);
      void render(){}
      void update(){}
      void handleEvents(){}
      void clean(){}

      // a function to access the private running variable
      bool running() { return m_bRunning; }

    private:

      SDL_Window* m_pWindow;
      SDL_Renderer* m_pRenderer;
      bool m_bRunning;
};

#endif // defined(__Game__) */

Game.cpp

#include "Game.h"

bool Game::init(const char* title, int xpos, int ypos, int width, int height, int flags)
{
    // attempt to initialize SDL
    if(SDL_Init(SDL_INIT_EVERYTHING) == 0)
    {
    std::cout << "SDL init success\n";
    // init the window
    m_pWindow = SDL_CreateWindow(title, xpos, ypos,
    width, height, flags);

    if(m_pWindow != 0) // window init success
    {
        std::cout << "window creation success\n";
        m_pRenderer = SDL_CreateRenderer(m_pWindow, -1, 0);
        if(m_pRenderer != 0) // renderer init success
        {
        std::cout << "renderer creation success\n";
        SDL_SetRenderDrawColor(m_pRenderer,
        255,255,255,255);
        }
        else
        {
        std::cout << "renderer init fail\n";
        return false; // renderer init fail
        }
    }
    else
    {
        std::cout << "window init fail\n";
        return false; // window init fail
    }
    }
    else
    {
    std::cout << "SDL init fail\n";
    return false; // SDL init fail
    }
    std::cout << "init success\n";
    m_bRunning = true; // everything inited successfully, start main loop

    return true;
}


void Game::render()
{
    SDL_RenderClear(m_pRenderer); // clear the renderer to the draw color
    SDL_RenderPresent(m_pRenderer); // draw to the screen
}


void Game::clean()
{
    std::cout << "cleaning game\n";
    SDL_DestroyWindow(m_pWindow);
    SDL_DestroyRenderer(m_pRenderer);
    SDL_Quit();
}

void Game::handleEvents()
{
    SDL_Event event;
    if(SDL_PollEvent(&event))
    {
      switch (event.type)
      {
        case SDL_QUIT:
          m_bRunning = false;
        break;

        default:
        break;
      }
    }
}

Answer 1

You aren't compiling Game.cpp. Try:

g++ -o main main.cpp Game.cpp -I/usr/local/include/SDL2 -L/usr/local/lib -lSDL2

The problem is that although you #included Game.h in main.cpp, it references functions that are defined in Game.cpp. Without compiling that as well, the linker doesn't have the definitions required to make an executable.