Read graphs in graph6 and sparse6 format.
“graph6 and sparse6 are formats for storing undirected graphs in a compact manner, using only printable ASCII characters. Files in these formats have text type and contain one line per graph.” http://cs.anu.edu.au/~bdm/data/formats.html
See http://cs.anu.edu.au/~bdm/data/formats.txt for details.