GLEW _First was nullptr

Question

So I have been working on a game through C++ with GLFW and GLEW and everything was going fine until I implemented GLEW then I get an error that I have never encountered before and I don't have the foggiest on what to do, I have googled it and done some research but to no avail. I have noticed that in the stack frame section it says something to do with this line of code in my main.cpp

std::cout << glGetString(GL_VERSION) << std::endl;

Also it says something to do with memory. I'll leave the rest of my code down below and if there's any info you need just ask and I will try my best to provide it

So I just discovered if i take out

std::cout << glGetString(GL_VERSION) << std::endl;

then it works however the window isn't created.

Where do I go from here? Any idea?

   #include "src\graphics\window.h"
int main() {
    using namespace benji;
    using namespace graphics;

    Window window("Benji Engine", 1280, 720);
    glClearColor(0.2f, 0.3f, 0.8f, 1.0f);
    std::cout << glGetString(GL_VERSION) << std::endl;``

    while (!window.closed()) {
        std::cout << window.getWidth() << ", " << window.getHeight() << std::endl;
        window.clear();
        glBegin(GL_TRIANGLES);
        glVertex2f(-0.5f, -0.5f);
        glVertex2f(0.0f, 0.5f);
        glVertex2f(0.5f, -0.5f);
        glEnd();
        window.update();
    }

    return 0;
}

main.h

 #pragma once
    class main
    {
    public:
        main();
        ~main();
    };

window.cpp

#include "window.h"

namespace benji { namespace graphics {


void windowResize(GLFWwindow *window, int width, int height);

Window::Window(const char *title, int width, int height) {
    m_Title = title;
    m_Width = width;
    m_Height = height;
    if (!init()) {
        glfwTerminate();
    }

}

Window::~Window() {
    glfwTerminate();

}

bool Window::init() {
    if (!glfwInit()) {
        std::cout << "Failed to initialize GLFW!" << std::endl;
        return false;
    }

    m_Window = glfwCreateWindow(m_Width, m_Height, m_Title, NULL, NULL);
    if (!m_Window) {
        std::cout << "Failed to create GLFW window!" << std::endl;
        return false;
    }
    glfwMakeContextCurrent(m_Window);
    glfwSetWindowSizeCallback(m_Window, windowResize);

    if (glewInit != GLEW_OK) {
        std::cout << "GLEW FAILED!" << std::endl;
        return false;
    }
    return true;


}

void Window::clear() const {
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
}

void Window::update(){
    glfwPollEvents();
    glfwSwapBuffers(m_Window);


}

    bool Window::closed() const {
    return glfwWindowShouldClose(m_Window) == 1;
}

    void windowResize(GLFWwindow *window, int width, int height) {
        glViewport(0, 0, width, height);
    }
}}

window.h

 #pragma once
    #include <iostream>
    #include <GL\glew.h>
    #include <GLFW\glfw3.h>

namespace benji {
    namespace graphics {
        class Window {
        private:
            const char *m_Title;
            int m_Width, m_Height;
            GLFWwindow *m_Window;
            bool m_Closed;

        public:
            Window(const char *title, int width, int height);
            ~Window();
            bool closed() const;
            void update();
            void clear() const;

             int getWidth() const {
                return m_Width;

            }
             int getHeight() const { return m_Height; }
        private:
            bool init();

        };
}

}

What is the full error? And do you have a debug callstack or any other information? — ssell, Feb 23 '17 at 20:09
The only other error I can see is Exception thrown: read access violation. _First was nullptr. — Ryan Midgley, Feb 23 '17 at 20:23
If `glGetString` is indeed crashing, it is because your OpenGL has not been properly initialized. Are you getting any error outputs during your `Window::init`? This is also supported by the fact that when you remove the call to `glGetString` it does not crash, but no window is opened. See also "[Why Could glGetString(GL_VERSION) Be Causing a Seg Fault?](http://stackoverflow.com/questions/6288759/why-could-glgetstringgl-version-be-causing-a-seg-fault)" — ssell, Feb 23 '17 at 20:35
I have been following a tutorial to initialize OpenGL as it's the first time that I have done it and well it seems to be right to me,,, so im not sure. — Ryan Midgley, Feb 23 '17 at 21:04

score 1 · Answer 1 · answered Feb 23 '17 at 21:04

1

In Window.cpp:

if (glewInit != GLEW_OK) {
    std::cout << "GLEW FAILED!" << std::endl;
    return false;
}

glewInit() is a function, not a variable. You need to call it as a function. I'm surprised this even compiled.

All other OpenGL functions that come from after version 1.1 will throw errors to the effect of ACCESS_VIOLATION READING ADDRESS 0x00000000 or some similar error, because if glewInit() is not properly called, none of the function macros provided by GLEW will point to valid function pointers.

answered Feb 23 '17 at 21:04

Xirema

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`I'm surprised this even compiled`, so am I if this wasn't just an error in copying the code over to the question. But good catch, I managed to look right past it multiple times. – ssell Feb 23 '17 at 21:17
@ssell I stopped using GLEW a while ago (switched to glBinding) and can't remember if GLEW makes everything decay to function pointers, or just the `gl*` functions themselves. If it does it for everything, that would at least explain why the program compiles (but doesn't run correctly). – Xirema Feb 23 '17 at 21:19
So would you recommend not using GLEW? – Ryan Midgley Feb 23 '17 at 21:26
@RyanMidgley I'm not going to make recommendations on that front. I personally like the interface for glBinding more than I like the interface for GLEW, but not everyone is going to feel the same way. – Xirema Feb 23 '17 at 21:32
Just gonna let you know how I fixed it, I forgot the parenthesis after glewInit. Something really insignificant but that's the issue haha – Ryan Midgley Feb 24 '17 at 06:39

GLEW _First was nullptr

1 Answers1