Re: Cyclomatic complexity

[ltroeger@intermetrics.com]

I have used cyclomatic complexity in different ways and found it useful. 
In a study on Space Shuttle code, I found a direct correlation between
modules whose cyclomatic complexity exceeded the threshold of 10 and the
number and severity of errors discovered in those modules.  I am now
using the McCabe toolset (which has other metrics and tools to compensate
for the weaknesses in cyclomatic complexity itself) to focus independent
verification and validation efforts on modules that have high cyclomatic
and essential complexity measures in embedded flight software code.  I
have found, again, that modules whose metrics exceed those thresholds are
much more prone to error.  I should qualify this by saying that the code
is written in C and is structured - I don't know how useful this would be
on object-oriented code, and, indeed, McCabe and Assoc. have a new set of
metrics and tools for object-oriented code.  Also, integration issues
such as global data problems, issues with tasking, and re-entrancy are
not well addressed by the tool, and certainly not by the cyclomatic
complexity measure itself.

There is a complete discussion of all this in the NIST publication 500-235
"Structured Testing: A Testing Methodology Using the Cyclomatic Complexity
Metric".  It can be found on the McCabe website at:

http://www.mccabe.com/nist

The integration question is addressed in here as well.

Lea Anne Troeger
Program Area Technical Lead
Automated/Robotic Spacecraft IV&V
Intermetrics, Inc.
ltroeger@intermetrics.com

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