c code to display the contents of a text file using opengl

Assuming this for quality rendering of text on an OpenGL capable device:

You can start by diving into Chris Greens' Valve Paper[^]

You would typically use something like freetype[^] to retrive the outlines of the glyphs used to render the text.

Trivial rendering can be achieved by doing something like this:
Drawing Text in a Double-Buffered OpenGL Window[^]

Best regards
Espen Harlinn