Tool to generate flowcharts for C sourceshttp://www.gnu.org/software/cflow
GNU cflow analyzes a collection of C source files and prints a graph, charting
control flow within the program. GNU cflow 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.