OpenGL and GL3W support issues - c++

Question

There is something strange happening with gl3w's isSupported function. When I call isSupported(4, 0) it returns false, meaning OpenGL 4.0 isn't supported. However, when I call glGetString(GL_VERSION) it says OpenGL version 4.0.
Does this mean I can use OpenGL 4.0 functions?
I'm using gl3w in C++ and Visual Studio 2017
#include <GL/gl3w.h>
#include <GLFW/glfw3.h>
int main(int argc, char** argv){
if(!glfwInit()) {
FATAL_ERROR("Failed to initialise GLFW");
}
glfwSetErrorCallback(glfwErrorCallback);
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 2);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 0);
GLFWwindow* window = glfwCreateWindow(640, 480, "OpenGL", nullptr, nullptr);
//If i put glfwMakeContextCurrent here gl3wInit fails
//glfwMakeContextCurrent(window);
if (!window) {
glfwTerminate();
FATAL_ERROR("Window creation failed");
}
if(!gl3wInit()) {} // handle that
glfwMakeContextCurrent(window);
bool support = gl3wIsSupported(4, 0); // returns false
const char* version = glGetString(GL_VERSION); // return "4.0.0"
}

Answer 1

You have to make a GL context current before you call gl3wInit() or regular OpenGL functions otherwise they won't do anything useful.

Answer 2

In the OpenGL wiki you can read:
The GL3W library focuses on the core profile of OpenGL 3 and 4. It
only loads the core entrypoints for these OpenGL versions. It supports
Windows, Mac OS X, Linux, and FreeBSD.
Note: GL3W loads core OpenGL
only by default. All OpenGL extensions will be loaded if the --ext
flag is specified to gl3w_gen.py.
And this is confirmed looking inside the code:
int gl3wIsSupported(int major, int minor)
{
if (major < 3) // <<<<=========== SEE THIS
return 0;
if (version.major == major)
return version.minor >= minor;
return version.major >= major;
}
You are asking with glfwWindowHint for an old 2.0 version. Thus, gl3wIsSupported will return false and gl3wInit will return GL3W_ERROR_OPENGL_VERSION.
For glGetString(GL_VERSION) returning "4.0" means that, yes, you can use that 4.0 version. Ask for it with glfwWindowHint.

Answer 3

I fixed it by switching over to glad instead
if (!glfwInit()) {
FATAL_ERROR("Failed to initialise GLFW");
}
glfwSetErrorCallback(glfwErrorCallback);
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 2);
GLFWwindow* window = glfwCreateWindow(640, 480, "OpenGL", nullptr, nullptr);
if (!window) {
glfwTerminate();
FATAL_ERROR("Window creation failed");
}
glfwMakeContextCurrent(window);
if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress)) {
glfwDestroyWindow(window);
glfwTerminate();
FATAL_ERROR("Failed to initialise OpenGL context");
}
PRINT("OpenGL Version: " << GLVersion.major << "." << GLVersion.minor);