How do I change the font of a GtkText widget?

There are a couple of ways of doing this. As GTK+ allows the appearance of applications to be changed at run time using resources you can use something like the following in the appropriate file:

style "text"
  font = "-adobe-helvetica-medium-r-normal--*-100-*-*-*-*-*-*"

Another way to do this is to load a font within your program, and then use this in the functions for adding text to the text widget. You can load a font using, for example:

  GdkFont *font;
  font = gdk_font_load("-adobe-helvetica-medium-r-normal--*-140-*-*-*-*-*-*");