carl@CITHEX.CALTECH.EDU.UUCP (03/24/87)
The following procedure demonstrates a bug in DIFF.EXE as it exists under VMS
V4.5. A class of files that cause this bug to manifest itself can be described
as follows: One file has one more record than the other file. All records in
the second file differ from those in the first. When DIFF is involked with the
/MAXIMUM_DIFFERENCES qualifier given a value equal to the number of records in
the file with fewer, DIFF goes into an infinite (I think; I haven't outwaited
the loop yet, though, and the only way it's likely to exit from the loop is if
some sort of internal stack overflows or it hits some resource limit) loop.
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$ create/fdl=sys$input: diff.dat !create a file with known attributes
RECORD !specify record attributes
FORMAT VARIABLE !variable length records
SIZE 0 !no maximum record size
$ open/append file diff.dat !now we populate it
$ write file "$" !write an arbitrary record
$ write file "-" !write an arbitrary record
$ close file !we're done with this file
$ create/fdl=sys$input: diff.dat !create a file with known attributes
RECORD !specify record attributes
FORMAT VARIABLE !variable length records
SIZE 0 !no maximum record size
$ open/append file diff.dat !now we populate it
$ write file "!" !this record's different from the others
$ close file !we're done with this file
$ on control_y then delete diff.dat;* !prepare to do the cleanup when the user
$ diff/max=1 diff.dat !control-y's out of the infinite loop
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Has anybody else run into/reported this bug (or better yet, fixed it)?