[Rcpp-devel] [Segfault Reason] Beginner Question: Same code *sometimes* fails due to segfault sometimes

Hi Rcpp-users:

I am a very happy user of Rcpp. I am a statistician who can code a bit. Recently, I have been working on making my cross validation code run faster using Rcpp.

I have a question and wanted to check if others have faced similar problems.

My code sometimes fails with a segmentation fault error, however this behavior cannot be replicated. That is, most of the times it runs fine and gives appropriate results, but once in a while it will fail due to segmentation fault and gives error like -- 

 *** caught segfault ***
address 0x18, cause 'memory not mapped'

I don't think this is normal, but how can it give correct answers when it runs correctly. Any ideas?

I would be happy to share code, but I wanted to see if I am missing something here. (I have limited experience as a C++ programmer.) 

Thanks in advance for your help.

Best Regards,
S.

My code sometimes fails with a segmentation fault error, however this behavior cannot be replicated. That is, most of the times it runs fine and gives appropriate results, but once in a while it will fail due to segmentation fault and gives error like -- 

 *** caught segfault ***
address 0x18, cause 'memory not mapped'

I don't think this is normal, but how can it give correct answers when it runs correctly. Any ideas?

On 2011-05-20, at 12:59 AM, Sunny Srivastava wrote:

My code sometimes fails with a segmentation fault error, however this
behavior cannot be replicated. That is, most of the times it runs fine and
gives appropriate results, but once in a while it will fail due to
segmentation fault and gives error like --

 *** caught segfault ***
address 0x18, cause 'memory not mapped'

I don't think this is normal, but how can it give correct answers when it
runs correctly. Any ideas?

It's sheer chance that your code is not segfaulting every time it's running.
This error means your program is trying to access memory that does not belong
to it. Something that was allocated was freed, or it was never allocated in
the first place, but is still being accessed.

As Romain suggested, post the code that causes this. If it's really long, try
to narrow it down to a small reproducible example.

Davor