Drawing two triangles using index buffer - c++

Question

I am following Cherno's brilliant series on OpenGL, and I have encountered a problem. I have moved on from using a vertex buffer only, to now using a vertex buffer together with an index buffer.
What I want to happen, is for my program to draw two triangles, using the given positions and indices, however when I run my program I only get a black screen. My shaders are working fine when drawing only from a vertex buffer, but introducing the index buffer makes it fail. Here is the relevant parts of code:
float positions[] {
-0.5, -0.5,
0.5, -0.5,
0.5, 0.5,
-0.5, 0.5
};
unsigned int indices[] {
0, 1, 2,
2, 3, 0
};
unsigned int VBO;
glGenBuffers(1, &VBO);
glBindBuffer(GL_ARRAY_BUFFER, VBO);
glBufferData(GL_ARRAY_BUFFER, 4*2*sizeof(float), positions, GL_STATIC_DRAW);
glEnableVertexAttribArray(0);
glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, sizeof(float)*2, 0);
unsigned int IBO;
glGenBuffers(1, &IBO);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, IBO);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, 6*sizeof(unsigned int), indices, GL_STATIC_DRAW);
ShaderProgramSource source = parseShader("res/shaders/Basic.glsl");
unsigned int shader = createShader(source.vertexSource, source.fragmentSource);
glUseProgram(shader);
/* Loop until the user closes the window */
while (!glfwWindowShouldClose(window))
{
/* Render here */
glClear(GL_COLOR_BUFFER_BIT);
glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, nullptr);
/* Swap front and back buffers */
glfwSwapBuffers(window);
/* Poll for and process events */
glfwPollEvents();
}
I am pretty much sure that my code is equal to that of Cherno, but he gets a nice looking square on screen whereas I get nothing. Can you spot an error?
Here's some info on my system:
macOS 12.2.1
OpenGL Version 4.1
GLSL Version 3.3
Writing and compiling in Xcode
Static linking to GLEW and GLFW

Answer 1

Unlike using Linux or Windows, a Compatibility profile OpenGL Context is not supported on a Mac. You must use a Core profile OpenGL Context. If you use a Core profile, you must create a Vertex Array Object because a core profile does not have a default Vertex Array Object.
GLuint vao;
glGenVertexArrays(1, &vao);
glBindVertexArray(vao);
glEnableVertexAttribArray(0);
glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, sizeof(float)*2, 0);