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C++ Problem with enum and binary or operator

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Why wont this code compile? How do i get this to compile (VC++ 2015)?

typedef enum fpl_InitFlag {
	fpl_InitFlag_None = 0,
	fpl_InitFlag_Window = 1 << 0,
	fpl_InitFlag_VideoOpenGL = 1 << 1,
} fpl_InitFlag;

static void InitSomething(fpl_InitFlag initFlags) {
	if (initFlags & fpl_InitFlag_VideoOpenGL) {
		initFlags |= fpl_InitFlag_Window;
	}
}
int main(int argc, char **args) {
	InitSomething(fpl_InitFlag_VideoOpenGL);
	return 0;
}

Error C2676    binary '|=': 'fpl_InitFlag' does not define this operator or a conversion to a type acceptable to the predefined operator

Error (active)        this operation on an enumerated type requires an applicable user-defined operator function

Edited by Finalspace

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Found a solution for C++ - not great that but will work:

inline fpl_InitFlag operator |(fpl_InitFlag a, fpl_InitFlag b) {
	return static_cast<fpl_InitFlag>(static_cast<int>(a) | static_cast<int>(b));
}
inline fpl_InitFlag operator &(fpl_InitFlag a, fpl_InitFlag b) {
	return static_cast<fpl_InitFlag>(static_cast<int>(a) & static_cast<int>(b));
}
inline fpl_InitFlag& operator |=(fpl_InitFlag& a, fpl_InitFlag b) {
	return a = a | b;
}

 

Edited by Finalspace

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I think using just enum and not enum class is the better option for bitfields, sadly. But i'm curious what comes up here... :)

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You can read this.

 

I personally don't like to do that just because doing arithmetic (including bitwise operations) on enums definitely lead to have values not defined in the enum. So you start with a finite set of elements and by allowing such operations you can end up with an infinite set of elements (if you limit to 'or' bitwise operations you are still stuck with a finite number of elements, but their number is large).

So typical C operations like a switch will not be able to handle easily all the values. Also, when debugging, the debugger will not be able to print the matching name of an enum value.

And if you are in C++, this tends to pervade the nature of your enumeration type.

This is just what I think about that :)

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The compiler is just trying to save you from writing buggy code.  You need to go out of your way to force your bugs into your software.  Your solution does a fine job of doing that.

You're implementing an operator that is not closed on the enumeration set.  You're breaking the contract provided by enum.  When you start getting weird errors, save yourself some debugging time and check where you use the enum first.

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51 minutes ago, Bregma said:

The compiler is just trying to save you from writing buggy code.  You need to go out of your way to force your bugs into your software.  Your solution does a fine job of doing that.

You're implementing an operator that is not closed on the enumeration set.  You're breaking the contract provided by enum.  When you start getting weird errors, save yourself some debugging time and check where you use the enum first.

A normal enum are just a single 32 bit integer value, including its field accessible by a constant.

You can even define which type your enum are. So using it as flags are totally valid, because its just a stupid integer.

And for the case the compiler may change it to maybe 64 bit integer, i dont care - because the binary operators works there as well.

 

There is no buggy code at all - its totally fine. I see no side-effects whatsoever - unless i overwrite the operators doing some weird shit.

 

Sure i could change it to enum class, but this will break C compability entirely and for a C library this is no go!

Edited by Finalspace

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I've found the following pattern to be effective:

#include <stdio.h>
  
constexpr const unsigned flag[]                                                                                                                                    
= {                                                                                                                                                                
	0, 1, 2, 4, 8, 16, 32, 64, 128, 256                                                                                                                            
};                                                                                                                                                                 
                                                                                                                                                                   
struct fpl                                                                                                                                                         
{                                                                                                                                                                  
	enum init_flag                                                                                                                                                 
	{                                                                                                                                                              
		init_none,                                                                                                                                                 
		init_window,                                                                                                                                               
		init_opengl                                                                                                                                          
	};                                                                                                                                                             
                                                                                                                                                                   
	fpl( const unsigned &iflags )                                                                                                                                  
	: init_flags{ iflags }                                                                                                                                         
	{}                                                                                                                                                             
                                                                                                                                                                   
	unsigned init_flags;                                                                                                                                           
};                                                                                                                                                                 
                                                                                                                                                                   
                                                                                                                                                                   
int main( int argc, const char *args[] )                                                                                                                           
{                                                                                                                                                                  
	fpl my_fpl{ flag[ fpl::init_window ] | flag[ fpl::init_opengl ] };                                                                                       
                                                                                                                                                                   
	printf( "my_fpl flags: 0x%X\n", my_fpl.init_flags );                                                                                                           
                                                                                                                                                                   
	return 0;                                                                                                                                                      
}                                                                                                                                                                  

 

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I think using enumerations as flags is fine.  The whole argument that 'its bad because they're not supposed to be used that way' I think is kinda silly.  Sure you don't want to have a situation where you accidentally create an undefined bit pattern, but whether that bit pattern is an 'enum' or just an uint32_t, you still have the same error.  It'll be the same problem in the same piece of code.  The nice thing about enum's is you can have nicer names and avoid stuff like VK_STRUCTURE_TYPE_IMPORT_MEMORY_WIN32_HANDLE_INFO_NV.

Here is what I use (formatting is a bit off but you get the idea):

// --------------------------------------------------------------------------------------------------------------------------
//	enumeration expansion
//		- ENUM_CLASS_OPERATORS defines standard bit operators for enum class types
//		- ENUM_CLASS_AND_OR defines only 'and' and 'or'
// --------------------------------------------------------------------------------------------------------------------------

# define ENUM_CLASS_OPERATORS(T)																																					\
inline constexpr T operator~(T a) noexcept { return static_cast<T>(~static_cast<uint64_t>(a)); }														\
inline constexpr T operator&(T a, T b) noexcept { return static_cast<T>(static_cast<uint64_t>(a) & static_cast<uint64_t>(b)); }			\
inline constexpr T operator|(T a, T b) noexcept { return static_cast<T>(static_cast<uint64_t>(a) | static_cast<uint64_t>(b)); }			\
inline constexpr T operator^(T a, T b) noexcept { return static_cast<T>(static_cast<uint64_t>(a) ^ static_cast<uint64_t>(b)); }			\
inline T& operator&=(T& a, T b) noexcept { return a = static_cast<T>(static_cast<uint64_t>(a) & static_cast<uint64_t>(b)); }			\
inline T& operator|=(T& a, T b) noexcept { return a = static_cast<T>(static_cast<uint64_t>(a) | static_cast<uint64_t>(b)); }				\
inline T& operator^=(T& a, T b) noexcept { return a = static_cast<T>(static_cast<uint64_t>(a) ^ static_cast<uint64_t>(b)); }

# define ENUM_CLASS_AND_OR(T)																																						\
inline constexpr T operator&(T a, T b) noexcept { return static_cast<T>(static_cast<uint64_t>(a) & static_cast<uint64_t>(b)); }			\
inline constexpr T operator|(T a, T b) noexcept { return static_cast<T>(static_cast<uint64_t>(a) | static_cast<uint64_t>(b)); }			\
inline T& operator&=(T& a, T b) noexcept { return a = static_cast<T>(static_cast<uint64_t>(a) & static_cast<uint64_t>(b)); }			\
inline T& operator|=(T& a, T b) noexcept { return a = static_cast<T>(static_cast<uint64_t>(a) | static_cast<uint64_t>(b)); }	

The thing to consider is, even with bit operators, its actually quite hard to come up with a bit pattern that's undefined.  Most of code with flags looks something like:

enum class EEnumOptions {
  none,
  option_1,
  option_2,
  option_3,
  };

enum class EEnumFlags {
  none = 0,
  flag_a = 1,
  flag_b = 2,
  flag_c = 4,
  };
ENUM_CLASS_AND_OR(EEnumFlags)	// create 'and' and 'or' bit operators for EEnumName
  
// ....

void Func(EEnumOptions e, EEnumFlags f) {
  
  // handle options
  switch (e) {
    case EEnumOptions::option_1:
    case EEnumOptions::option_2:
    case EEnumOptions::option_3:
    }
  
  // handle flags
  if ((f & EEnumName::flag_a) == EEnumName::flag_a) {}		// flag_a is set
  if ((f & EEnumName::flag_b) == EEnumName::flag_b) {}		// flag_b is set
  if ((f & EEnumName::flag_c) != EEnumName::flag_c) {}		// flag_c is not set
  }

Even if you were to make a silly bit pattern, things won't 'blow up'.  Any bit pattern is still well defined.  Also if you only restrict yourself to 'and' and 'or' (ie. don't overload 'not' and 'xor'), then its near impossible to create undefined bit patterns (short of intentionally static_cast'ing them in).  Its still safer then simply integer constants or #define's, and for the most part self documenting.  I don't think anyone would have any difficulty using that function, or understanding what is expected, and passing an undefined bit pattern would have to be intentional.

Maybe its my own personal preference, but this seems clean, easy to understand, and hard to break; and isn't that what we want?

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      #shader vertex #version 330 core layout(location = 0) in vec4 aPos; layout(location = 1) in vec2 aTexCoord; out vec2 t_TexCoord; uniform mat4 u_MVP; void main() { gl_Position = u_MVP * aPos; t_TexCoord = aTexCoord; } #shader fragment #version 330 core out vec4 aColor; in vec2 t_TexCoord; uniform sampler2D u_Texture; void main() { aColor = texture(u_Texture, t_TexCoord); } Also i'm pretty sure that every time i'm hitting the up, down, left and right arrows on the keyboard, i'm changing the model Matrix of the Player and not the others.
       
      Window Class:
      #include "Window.h" #include <GL/glew.h> #include <GLFW/glfw3.h> #include "Error.h" #include "Renderer.h" #include "Scene.h" #include "Input.h" //Global Variables. int screen_width, screen_height; //On Window Resize. void OnWindowResize(GLFWwindow *window, int width, int height); //Implementation Structure. struct Window::Implementation { //GLFW Window. GLFWwindow *GLFW_window; //Renderer. Renderer *renderer; //Delta Time. double delta_time; //Frames Per Second. int fps; //Scene. Scene *scnene; //Input. Input *input; //Deconstructor. ~Implementation(); }; //Window Constructor. Window::Window(std::string title, int width, int height) { //Initializing width and height. screen_width = width; screen_height = height; //Create Pointer To Implementation. m_Impl = new Implementation(); //Try initializing GLFW. if (!glfwInit()) { std::cout << "GLFW could not be initialized!" << std::endl; std::cout << "Press ENTER to exit..." << std::endl; std::cin.get(); exit(-1); } //Setting up OpenGL Version 3.3 Core Profile. glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3); glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3); glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE); /* Create a windowed mode window and its OpenGL context */ m_Impl->GLFW_window = glfwCreateWindow(width, height, title.c_str(), NULL, NULL); if (!m_Impl->GLFW_window) { std::cout << "GLFW could not create a window!" << std::endl; std::cout << "Press ENTER to exit..." << std::endl; std::cin.get(); glfwTerminate(); exit(-1); } /* Make the window's context current */ glfwMakeContextCurrent(m_Impl->GLFW_window); //Initialize GLEW. if(glewInit() != GLEW_OK) { std::cout << "GLEW could not be initialized!" << std::endl; std::cout << "Press ENTER to exit..." << std::endl; std::cin.get(); glfwTerminate(); exit(-1); } //Enabling Blending. GLCall(glEnable(GL_BLEND)); GLCall(glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA)); //Setting the ViewPort. GLCall(glViewport(0, 0, width, height)); //**********Initializing Implementation**********// m_Impl->renderer = new Renderer(); m_Impl->delta_time = 0.0; m_Impl->fps = 0; m_Impl->input = new Input(this); //**********Initializing Implementation**********// //Set Frame Buffer Size Callback. glfwSetFramebufferSizeCallback(m_Impl->GLFW_window, OnWindowResize); } //Window Deconstructor. Window::~Window() { delete m_Impl; } //Window Main Loop. void Window::MainLoop() { //Time Variables. double start_time = 0, end_time = 0, old_time = 0, total_time = 0; //Frames Counter. int frames = 0; /* Loop until the user closes the window */ while (!glfwWindowShouldClose(m_Impl->GLFW_window)) { old_time = start_time; //Total time of previous frame. start_time = glfwGetTime(); //Current frame start time. //Calculate the Delta Time. m_Impl->delta_time = start_time - old_time; //Get Frames Per Second. if (total_time >= 1) { m_Impl->fps = frames; total_time = 0; frames = 0; } //Clearing The Screen. m_Impl->renderer->Clear(0, 0, 0); //Render The Scene. if (m_Impl->scnene != NULL) m_Impl->scnene->Render(this); //Updating the Screen. m_Impl->renderer->Update(m_Impl->GLFW_window); //Increasing frames counter. frames++; //End Time. end_time = glfwGetTime(); //Total time after the frame completed. total_time += end_time - start_time; } //Terminate GLFW. glfwTerminate(); } //Load Scene. void Window::LoadScene(Scene * scene) { //Set the scene. m_Impl->scnene = scene; } //Get Delta Time. double Window::GetDeltaTime() { return m_Impl->delta_time; } //Get FPS. int Window::GetFPS() { return m_Impl->fps; } //Get Width. int Window::GetWidth() { return screen_width; } //Get Height. int Window::GetHeight() { return screen_height; } //Get Input. Input * Window::GetInput() { return m_Impl->input; } Renderer * Window::GetRenderer() { return m_Impl->renderer; } GLFWwindow * Window::GetGLFWindow() { return m_Impl->GLFW_window; } //Implementation Deconstructor. Window::Implementation::~Implementation() { delete renderer; delete input; } //OnWindowResize void OnWindowResize(GLFWwindow *window, int width, int height) { screen_width = width; screen_height = height; //Updating the ViewPort. GLCall(glViewport(0, 0, width, height)); }  
      Brain Class
      #include "Brain.h" #include "Sprite.h" #include "Window.h" struct Brain::Implementation { //Just A Flag. bool started; //Window Pointer. Window *window; //Sprite Pointer. Sprite *sprite; }; Brain::Brain(Window *window, Sprite *sprite) { //Create Pointer To Implementation. m_Impl = new Implementation(); //Initialize Implementation. m_Impl->started = true; m_Impl->window = window; m_Impl->sprite = sprite; } Brain::~Brain() { //Delete Pointer To Implementation. delete m_Impl; } void Brain::Start() { } void Brain::Update() { } Window * Brain::GetWindow() { return m_Impl->window; } Sprite * Brain::GetSprite() { return m_Impl->sprite; } bool Brain::GetStart() { return m_Impl->started; } void Brain::SetStart(bool value) { m_Impl->started = value; } Script Class (Its a Brain Subclass!!!)
      #include "Script.h" Script::Script(Window *window, Sprite *sprite) : Brain(window, sprite) { } Script::~Script() { } void Script::Start() { std::cout << "Game Started!" << std::endl; } void Script::Update() { Input *input = this->GetWindow()->GetInput(); Sprite *sp = this->GetSprite(); //Move this sprite. this->GetSprite()->Move(200 * this->GetWindow()->GetDeltaTime(), input->GetKeyDown("left"), input->GetKeyDown("right"), input->GetKeyDown("up"), input->GetKeyDown("down")); std::cout << sp->GetTag().c_str() << ".x = " << sp->GetPos()->x << ", " << sp->GetTag().c_str() << ".y = " << sp->GetPos()->y << std::endl; }  
      Main:
      #include "SpaceShooterEngine.h" #include "Script.h" int main() { Window w("title", 600,600); Scene *scene = new Scene(); Sprite *player = new Sprite("Resources/Images/player.png", "Player", 100,100); Sprite *other = new Sprite("Resources/Images/cherno.png", "Other", 400, 100); Sprite *other2 = new Sprite("Resources/Images/cherno.png", "Other", 300, 400); Brain *brain = new Script(&w, player); player->AddBrain(brain); scene->AddSprite(player); scene->AddSprite(other); scene->AddSprite(other2); w.LoadScene(scene); w.MainLoop(); return 0; }  
       
      I literally can't find what is wrong. If you need more code, ask me to post it. I will also attach all the source files.
      Brain.cpp
      Error.cpp
      IndexBuffer.cpp
      Input.cpp
      Renderer.cpp
      Scene.cpp
      Shader.cpp
      Sprite.cpp
      Texture.cpp
      VertexArray.cpp
      VertexBuffer.cpp
      VertexBufferLayout.cpp
      Window.cpp
      Brain.h
      Error.h
      IndexBuffer.h
      Input.h
      Renderer.h
      Scene.h
      Shader.h
      SpaceShooterEngine.h
      Sprite.h
      Texture.h
      VertexArray.h
      VertexBuffer.h
      VertexBufferLayout.h
      Window.h
    • By 3dmodelerguy
      So in the few different tutorials that I have seen for using C++ / SDL, the implementation of the camera does not effect how the player is rendered but how the the rest of the world is rendered. Instead of changing the position / offset of where the player is rendered, you change the position / offset of where the map and other entities are renderer.
      Out of curiosity, is this the standard (or maybe only) way of doing things when working with lower level code like C++ / SDL?
      While it makes logical sense to me, my experience in game dev has always been high level abstractions (game engines like Unity or even libraries like Love) so it just feels wrong but maybe all of those engines / tools do it the same way and the abstraction they provide just hides that fact.
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