const char* source_to_string(GLenum source) {
    switch (source) {
        case GL_DEBUG_SOURCE_API:
            return "GL_DEBUG_SOURCE_API";
        case GL_DEBUG_SOURCE_WINDOW_SYSTEM:
            return "GL_DEBUG_SOURCE_WINDOW_SYSTEM";
        case GL_DEBUG_SOURCE_SHADER_COMPILER:
            return "GL_DEBUG_SOURCE_SHADER_COMPILER";
        case GL_DEBUG_SOURCE_THIRD_PARTY:
            return "GL_DEBUG_SOURCE_THIRD_PARTY";
        case GL_DEBUG_SOURCE_APPLICATION:
            return "GL_DEBUG_SOURCE_APPLICATION";
        case GL_DEBUG_SOURCE_OTHER:
            return "GL_DEBUG_SOURCE_OTHER";
        default:
            return "INVALID_SOURCE";
    }
}

const char* type_to_string(GLenum type) {
    switch (type) {
        case GL_DEBUG_TYPE_ERROR:
            return "GL_DEBUG_TYPE_ERROR";
        case GL_DEBUG_TYPE_DEPRECATED_BEHAVIOR:
            return "GL_DEBUG_TYPE_DEPRECATED_BEHAVIOR";
        case GL_DEBUG_TYPE_UNDEFINED_BEHAVIOR:
            return "GL_DEBUG_TYPE_UNDEFINED_BEHAVIOR";
        case GL_DEBUG_TYPE_PORTABILITY:
            return "GL_DEBUG_TYPE_PORTABILITY";
        case GL_DEBUG_TYPE_PERFORMANCE:
            return "GL_DEBUG_TYPE_PERFORMANCE";
        case GL_DEBUG_TYPE_MARKER:
            return "GL_DEBUG_TYPE_MARKER";
        case GL_DEBUG_TYPE_PUSH_GROUP:
            return "GL_DEBUG_TYPE_PUSH_GROUP";
        case GL_DEBUG_TYPE_POP_GROUP:
            return "GL_DEBUG_TYPE_POP_GROUP";
        case GL_DEBUG_TYPE_OTHER:
            return "GL_DEBUG_TYPE_OTHER";
        default:
            return "INVALID_TYPE";
    }
}

const char* severity_to_string(GLenum severity) {
    switch (severity) {
        case GL_DEBUG_SEVERITY_LOW:
            return "GL_DEBUG_SEVERITY_LOW";
        case GL_DEBUG_SEVERITY_MEDIUM:
            return "GL_DEBUG_SEVERITY_MEDIUM";
        case GL_DEBUG_SEVERITY_HIGH:
            return "GL_DEBUG_SEVERITY_HIGH";
        case GL_DEBUG_SEVERITY_NOTIFICATION:
            return "GL_DEBUG_SEVERITY_NOTIFICATION";
        default:
            return "INVALID_SEVERITY";
    }
}

void gl_log_func(GLenum source, GLenum type, GLuint id, GLenum severity, GLsizei length, const GLchar* message, const void* userParam) {
    fprintf(stdout, "source: %s, type: %s, id: %u, severity: %s, msg: %s\n",
            source_to_string(source),
            type_to_string(type),
            id,
            severity_to_string(severity),
            message);
    fflush(stdout);
}

...
glEnable(GL_DEBUG_OUTPUT);
glDebugMessageCallback(gl_log_func, 0);
glDebugMessageControl( GL_DONT_CARE, GL_DONT_CARE, GL_DEBUG_SEVERITY_NOTIFICATION, 0, 0, GL_FALSE)