GNU cflow analyzes a collection of C source files and prints a graph
charting control flow within the program.

Current implementation is able to produce both direct and inverted
flowgraphs for C sources. Optionally a cross-reference listing can
be generated. Two output formats are implemented: POSIX and GNU
(extended).

Input files can optionally be preprocessed before analyzing.

WWW: http://savannah.gnu.org/projects/cflow