I _think_ the relevant section of the C standard is 6.5.6 Additive Operators Par 8, excerpted here:
> If both the pointer operand and the result point to elements > of the same array object, or one past the last element of the > array object, the evaluation shall not produce an overflow; > otherwise, **the behavior is undefined**. This is from the [C11 draft][1], though I imagine has been part of the standard for a while. So by doing id[-1], in this case the pointer operand is id, and the result is one element _before_ the array object, thus undefined behavior which is bad news. I'm not an expert in these matters though. [1]: http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf On Thursday, March 5, 2020, 11:39:38 AM EST, Therneau, Terry M., Ph.D. via R-devel <r-devel@r-project.org> wrote: I ended up finding the issue by a focused code review. Once in the past, I had a version that would fail under one architecture but not another, in that case some help from Brian Ripley pointed me to the offending line of C code. That line read, but did not write, at an invalid memory location. Starting with the question of "what C routines have I added or modified most recently" along with where the fault appeared to occur in my test suite, I started reading C code and found one. Revised code passes tests on the winbuilder site. For the curious, I had a line asking "is this patient id different than the last patient id" in the C routine underneath survcheck(); I'm making sure that patients don't go backwards in time. Essentially for (i=0; i< n; i) { if (id[i] != id[i-1] ) { ...} It is still a surprise to me that just LOOKING at this out of range element would cause a failure, [i-1] never appears on the left hand side of any expressions in the ... chunk above. Nevertheless, it was an error. Que sera sera A strong thanks to those who gave solid suggestions for bringing up a local copy of Windows. Terry T >>> My latest submission of survival3.1-10 to CRAN fails a check, but only on >>> windows, which >>> I don't use. >>> How do I track this down? >>> The test in question works fine on my Linux box. >>> >>> Terry >>> >>> >>> >>> [[alternative HTML version deleted]] >>> >>> ______________________________________________ >>> R-devel@r-project.org mailing list >>> https://stat.ethz.ch/mailman/listinfo/r-devel >>> >> [[alternative HTML version deleted]] >> >> ______________________________________________ >> R-devel@r-project.org mailing list >> https://stat.ethz.ch/mailman/listinfo/r-devel >> [[alternative HTML version deleted]] ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
