Unhandled exception at 0x777122D2 (ntdll.dll) in ArticxEngine.exe: 0xC0000005: Access violation writing location 0x00000004

Question

I'm completely unsure of why I'm getting this error in VS2012 when I run my program. Visual Studio seemed to direct the problem towards sf::RenderWindow Articx::window; in Articx.cpp

Unhandled exception at 0x777122D2 (ntdll.dll) in ArticxEngine.exe: 0xC0000005: Access violation writing location 0x00000004.

Code Articx.h

#pragma once

#include <SFML/Graphics.hpp>
#include <SFML/Window.hpp>

class Articx
{
    public:
        static void Start();
    private:
        static void GameLoop();

        static bool isExiting();

        enum ScreenState {before, splash1, splash2, splash3, menu, pause, playing, exit};
        static ScreenState currentState;

        static sf::RenderWindow window;
};

Code Articx.cpp

#include <SFML/Graphics.hpp>
#include <SFML/System.hpp>
#include <SFML/Window.hpp>
#include <iostream>
#include <string>
#include "Articx.h"

inline void Message(char message[]);
inline void CallError(int code, char message[]);

Articx::ScreenState Articx::currentState = Articx::before;
sf::RenderWindow Articx::window;

void Articx::Start()
{
    Message("Articx Engine 1.0 Initializing...");

    if(currentState != before)
        return;

    window.create(sf::VideoMode(800,600,32), "Articx Engine 1.0");
    currentState = playing;

    while (!isExiting())
    {
        Message("Engine Initialized");
        Articx::GameLoop();
    }

    window.close();
}

bool Articx::isExiting()
{
    if(currentState == exit)
        return true;
    else
        return false;
}

void Articx::GameLoop()
{
    sf::Event currentEvent;

    while ( window.pollEvent(currentEvent) )
    {
        switch(currentState)
        {
            case Articx::playing:
                {
                    window.clear(sf::Color(0,0,0));
                    window.display();

                    if ( currentEvent.type == sf::Event::Closed )
                        currentState = exit;
                    break;
                }
        }
    }

    window.display();
}

inline void CallError(int code, char message[])
{
    std::cout << "ERROR CODE - " << code << std::endl << message << std::endl << "Will now exit..." << std::endl;
    system("PAUSE");
}

inline void Message(char message[])
{
    std::cout << "AX-MESSAGE: " << message << std::endl;
}

Code main.cpp

#include "Articx.h"

using namespace std;

int main(int argc, char** argv)
{
    Articx::Start();
    return 0;
}

Answer 1

The "Bottom Line" Reason

The reason for the unhandled exception is because you defined Articx::window as a static variable.

The Technical Explanation

The exception was thrown because constructing an sf:RenderWindow invokes the following constructors in this order:

RenderWindow::RenderWindow()
Window::Window()
GlResource::GlResource()

The GlResource::GlResource() constructor attempts to lock a global mutex:

namespace
{
    // OpenGL resources counter and its mutex
    unsigned int count = 0;
    sf::Mutex mutex;
}


namespace sf
{
////////////////////////////////////////////////////////////
GlResource::GlResource()
{
    {
        // Protect from concurrent access
        Lock lock(mutex);

        // If this is the very first resource, trigger the global context initialization
        if (count == 0)
            priv::GlContext::globalInit();

        // Increment the resources counter
        count++;
    }

    // Now make sure that there is an active OpenGL context in the current thread
    priv::GlContext::ensureContext();
}

The problem is that both your Articx::window and SFML's sf::Mutex mutex are global/static variables that are constructed at program initialization time. Which one gets constructed first? In your case your window was constructed first, so the GlResource::GlResource() constructor attempted to lock an invalid sf::Mutex. Because the order of construction of global/static variables can be unpredictable, it is best to create your sf::RenderWindow object in a non-global location.

The Solution

In main.cpp, create your sf::RenderWindow object within main(), passing a reference to window via Articx::Start():

#include "Articx.h"

using namespace std;

int main(int argc, char** argv)
{
    sf::RenderWindow window;

    Articx::Start(window);
    return 0;
}

In Articx.h, remove the static member variable window, and expand Start() and Gameloop() to accept an sf::RenderWindow reference:

#pragma once

#include <SFML/Graphics.hpp>
#include <SFML/Window.hpp>

class Articx
{
    public:
        static void Start(sf::RenderWindow &window);
    private:
        static void GameLoop(sf::RenderWindow &window);

        static bool isExiting();

        enum ScreenState {before, splash1, splash2, splash3, menu, pause, playing, exit};
        static ScreenState currentState;
};

In Articx.cpp, remove the global definition of window and modify Start() and Gameloop() to accept and use the passed sf::RenderWindow reference:

void Articx::Start(sf::RenderWindow &window)
{
    Message("Articx Engine 1.0 Initializing...");

    if(currentState != before)
        return;

    window.create(sf::VideoMode(800,600,32), "Articx Engine 1.0");
    currentState = playing;

    while (!isExiting())
    {
        Message("Engine Initialized");
        Articx::GameLoop(window);
    }

    window.close();
}

. . .

void Articx::GameLoop(sf::RenderWindow &window)
{
    . . .
}

Running it now displays the window correctly:

The window seems to have an endless loop printing "Engine Initialized", but I leave that to you :-).