libgpif (GnuPlot InterFace) is a bare metal simple as hell C Interface to
GNUPlot. In fact it's a rather generic read/write IPC tool at the moment that I
happen to use with GNUPlot. 

Maybe sometime there will be abstractions to GNUPlot's command set but imho this
simplistic approach offers the highest degree of flexibility.

If you're looking for something more sophisticated you might want to have a look
at http://ndevilla.free.fr/gnuplot/.

This library has been written with Linux as a target operating system in mind
but it'll probably be easy to port to anything else which adheres to the POSIX
standard (mostly in terms of process handling).

For install instructions have a look at INSTALL.txt.

API documentation in HTML format can be found in the doc directory. Also,
test/gpif_testcase.c should give you a pretty good idea of how to use the
library.