OpenGL not rendering anything after following tutorial

Question

I recently started following an OpenGL tutorial series by TheCherno on youtube.
Here is my code:

#include <GL/glew.h>
#include <GLFW/glfw3.h>

#include <iostream>
#include <fstream>
#include <string>
#include <sstream>

struct ShaderProgramSource {
    std::string VertexSource;
    std::string FragmentSource;
};

static ShaderProgramSource ParseShader(const std::string& filepath) {
    std::ifstream stream(filepath);

    enum class ShaderType {
        NONE = -1, VERTEX = 0, FRAGMENT = 1
    };

    std::string line;
    std::stringstream ss[2];
    ShaderType type = ShaderType::NONE;
    while (getline(stream, line)) {

        if (line.find("#shader") != std::string::npos) {

            if (line.find("vertex") != std::string::npos)
                type = ShaderType::VERTEX;
            else if (line.find("fragment") != std::string::npos)
                type = ShaderType::FRAGMENT;

        } else {
            ss[(int)type] << line << '\n';
        }
    }

    return { ss[0].str(), ss[1].str() };
}

static unsigned int CompileShader(unsigned int type, const std::string& source) {

    std::cout << "Compiling " << (type == GL_VERTEX_SHADER ? "vertex" : "fragment") << " shader..." << std::endl;

    unsigned int id = glCreateShader(type);
    const char* src = source.c_str();
    glShaderSource(id, 1, &src, nullptr);
    std::cout << glGetError() << std::endl;

    glCompileShader(id);
    std::cout << glGetError() << std::endl;

    int result;
    glGetShaderiv(id, GL_COMPILE_STATUS, &result);
    std::cout << glGetError() << std::endl;

    if (result == GL_FALSE) {
        int length;
        glGetShaderiv(id, GL_INFO_LOG_LENGTH, &length);
        std::cout << glGetError() << std::endl;

        char* message = (char*)alloca(length * sizeof(char));
        glGetShaderInfoLog(id, length, &length, message);
        std::cout << glGetError() << std::endl;

        std::cout << "Failed to compile" << (type == GL_VERTEX_SHADER ? "vertex" : "fragment") << " shader!" << std::endl;
        std::cout << message << std::endl;
        glDeleteShader(id);
        std::cout << glGetError() << std::endl;

        return 0;
    }

    std::cout << "Successfully compiled " << (type == GL_VERTEX_SHADER ? "vertex" : "fragment") << " shader!" << std::endl << std::endl;
    return id;
}

static unsigned int CreateShader(const std::string& vertexShader, const std::string& fragmentShader) {

    std::cout << "Creating shader..." << std::endl << std::endl;
    
    unsigned int program = glCreateProgram();
    unsigned int vs = CompileShader(GL_VERTEX_SHADER, vertexShader);
    unsigned int fs = CompileShader(GL_FRAGMENT_SHADER, fragmentShader);

    glAttachShader(program, vs);
    std::cout << glGetError() << std::endl;
    std::cout << "Attached vertex shader" << std::endl;

    glAttachShader(program, fs);
    std::cout << glGetError() << std::endl;
    std::cout << "Attached fragment shader" << std::endl;

    glLinkProgram(program);
    std::cout << glGetError() << std::endl;
    glValidateProgram(program);
    std::cout << glGetError() << std::endl;
    std::cout << "Linked and validated program" << std::endl;

    glDeleteShader(vs);
    std::cout << glGetError() << std::endl;
    std::cout << "Deleted vertex shader" << std::endl;

    glDeleteShader(fs);
    std::cout << glGetError() << std::endl;
    std::cout << "Deleted fragment shader" << std::endl;

    std::cout << "Succesfully created shader!" << std::endl << std::endl;

    return program;
}

int main(void)
{
    GLFWwindow* window;

    /* Initialize the library */
    if (!glfwInit())
        return -1;

    /* Create a windowed mode window and its OpenGL context */
    window = glfwCreateWindow(640, 480, "Hello World", NULL, NULL);
    if (!window)
    {
        glfwTerminate();
        return -1;
    }

    /* Make the window's context current */
    glfwMakeContextCurrent(window);

    if (glewInit() != GLEW_OK) {
        std::cout << "Error!" << std::endl;
    }

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

    float positions[6] = {
        -0.5f, -0.5f,
         0.0f,  0.5f,
         0.5f, -0.5f
    };

    unsigned int buffer;
    glGenBuffers(1, &buffer);
    std::cout << glGetError() << std::endl;
    glBindBuffer(GL_ARRAY_BUFFER, buffer);
    std::cout << glGetError() << std::endl;
    glBufferData(GL_ARRAY_BUFFER, 6*sizeof(float), positions, GL_STATIC_DRAW);
    std::cout << glGetError() << std::endl;

    glDisableVertexAttribArray(0);
    std::cout << glGetError() << std::endl;
    glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, sizeof(float)*2, 0);
    std::cout << glGetError() << std::endl;

    glBindBuffer(GL_ARRAY_BUFFER, 0);
    std::cout << glGetError() << std::endl;
    
    ShaderProgramSource source = ParseShader("res/shaders/Basic.shader");
    std::cout << "VERTEX" << std::endl;
    std::cout << source.VertexSource << std::endl;
    std::cout << "FRAGMENT" << std::endl;
    std::cout << source.FragmentSource << std::endl;

    //unsigned int shader = CreateShader(vertexShader, fragmentShader);
    ///glUseProgram(shader);


    
    // render loop
    while (!glfwWindowShouldClose(window))
    {
        /* Render here */
        glClear(GL_COLOR_BUFFER_BIT);

        glDrawArrays(GL_TRIANGLES, 0, 3);

        /* Swap front and back buffers */
        glfwSwapBuffers(window);

        /* Poll for and process events */
        glfwPollEvents();
    }

    //glDeleteProgram(shader);

    glfwTerminate();
    return 0;
}

Here's the Basic.shader file:

#shader vertex
#version 330 core  

layout(location = 0) in vec4 position;  

void main()  
{  
    gl_Position = position;  
}

#shader fragment
#version 330 core  

layout(location = 0) out vec4 color;  

void main()  
{  
    color = vec4(1.0, 0.0, 0.0, 1.0);  
}

I have tried using glGetError and it doesn't output any errors.

Answer 1

You need to enable the generic vertex attribute array instead of disabling it (see glEnableVertexAttribArray):

glDisableVertexAttribArray(0);

glEnableVertexAttribArray(0);

Furthermore, the code which compiles, linkes and installs the sahder is commented out:

//unsigned int shader = CreateShader(vertexShader, fragmentShader);
///glUseProgram(shader);

unsigned int shader = CreateShader(source.VertexSource, source.FragmentSource);
glUseProgram(shader);