If you want to write a C program that uses the URT, you should familiarize yourself with some existing applications. Three good places to start can be found in /IUS/usrc31/ray/urt-3.0/ on the suns:

tools/rleskel.c

URT command skeleton.

mwm/rle2gil.c

Very general RLE to GIL converter

mwm/getrow.c

Sample application. Extracts a scanline from an RLE file. Output is either the scanline in ASCII or an RLE image of the same dimensions with that row highlighted.