About selection and feedback

GLuint selectBuf[BUFSIZE]; gives the picked objects id (=name in OpenGL).
When you render your scene for picking, you have to affect at each object you want to able the picking an id (int), using glLoadName() ;

There is an example in glut: Glut\progs\demos\gliq

If you're using the selection buffer for picking purposes, and you aren't stacking names by pushing/popping, it should look something like this:

selectBuf[n+0] = 1, indicating no pushing/popping is going on
selectBuf[n+1] = minimum Z value
selectBuf[n+2] = maximum Z value
selectBuf[n+3] = name

I'm not familiar with the feedback mode, so if that's what you're looking for, disregard what I just said.

However, be warned: using the selection buffer [glRenderMode(GL_SELECT)] on ATI cards will have very poor performance results if the number of triangles being drawn is more than trivial. I believe the same applies when using it for feedback. I contacted ATI about it with little/no response. It works fine on NVidia cards, though.