Greg McGary <lcc.gm@UCLA-LOCUS.ARPA> (01/12/85)
I was recently bitten by a bug that caused me more trouble than it should
have. By doing a careful audit on the usage of certain flags and flag
words, I discovered that a flag test was and-ing the correct flag with
the wrong flag-word.
Determined to stamp out all bugs of this nature, I need an automated
method of detecting such inconsistencies. I have a couple of ideas:
1) Use a C language `enum' type to define the flag values, then
declare the flag word to be of that type so that the compiler
and/or lint can detect type clashes.
The problem with this approach is that I have no control over
the size of an `enum' variable or structure member. The C
Reference Manual says that `enum' variables have the same size
as `int'. I consider it evil to use `int' in structures-- one
should use `char', `short', or `long' since their size is quite
a bit less fuzzy.
2) Build a shell program using grep to audit the uses of a given
flag or flag-word.
The disadvantage here is that it is difficult to lexically
isolate expressions and thereby identify a flag/flag-word pair.
3) Build a syntax directed source analyzer to detect expressions
and audit flag/flag-word usage.
The disadvantages here are economic. It's just too damn much
work to build such a special purpose beast. Especially when
you consider that cpp manifest constants must remain un-expanded
for the thing to work at all.
Has anyone out there thought about this problem, and hopefully built
a tool to check for this type of error??
Please reply by mail. I'll summarize later. Thanx,
Greg McGary
Locus Computing Corp.
lcc!gm@ucla-cs
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