GNU cflow

GNU cflow is a flow graph generator that is part of the GNU Project. It reads a collection of C source files and generates a C flow graph of external references. It uses only sources and doesn't need to run the program.
History.
It was initially an implementation of the UNIX utility cflow.
cflow (UNIX utility).
cflow is a Unix command generating a C-language flowgraph.
Besides GNU, there are other implementations of "cflow", like the one for Tru64 Unix.