Declaring all display lists in a header file opengl

Question

I have file structure as

• display_list.hpp
• display_list.cpp
• file1.cpp

Now I want to use one of the display list in file1.cpp.

my display_list.hpp looks like

extern GLuint index;
void genDisplayList();

then display_list.cpp looks like

GLuint index = glGenLists(1);
void genDisplayList(){
    glNewList(index, GL_COMPILE);
    glBegin(GL_POLYGON);
    /*..vertex for polygon...*/
    glEnd();
    glEndList();
}

But when I tried to use glCallList(index) into my file1.cpp, I got nothing drawn on screen.

Answer 1

a) You should not use display lists. Display Lists have been deprecated with OpenGL-2 (the first drafts for OpenGL-2 removed them completely) and have been removed from OpenGL-3 and later.

b) To create a display list a valid OpenGL context is required to be active on the current thread. I presume you're calling genDisplayLists before there is a OpenGL context, for example if they're called by a constructor of a global scope object instance.