Will do, 
Thanks, 
Subramanya 

On Oct 28, 2013, at 2:53 PM, John Peterson <[email protected]> wrote:

> 
> 
> 
> On Sat, Oct 26, 2013 at 10:36 PM, Manav Bhatia <[email protected]> wrote:
> Good to know about this!
> 
> I did a bit of digging into it, and the problem seems to be coming after the 
> call to istr.unget() at line 990 in GetPot::_skip_whitespace(). For some 
> reason, it seems to corrupt the istream data structure so that std::cout << 
> istr   prints false.
> 
> Using istream::unget() seems to work OK outside of GetPot. Also, I downloaded 
> GetPot from its website and get the same issue.
> 
> I do not know why this is happening. Perhaps a bug with clang 5, or maybe 
> something about how GetPot does things.
> 
> I agree with your assessment.  In lldb (debugger for llvm/clang), istr.good() 
> == true immediately prior to line 990 and istr.good() == false immediately 
> following it.
> 
> One possible problem I can see with the getpot code: is it legal C++ to call 
> unget() immediately after a call to seekg or is it possibly invoking 
> undefined behavior?
> 
> Second: I'm not sure I even understand the logic of what's going on here.  
> You save "Pos", then if the current character is _not_ a comment character, 
> seekg(Pos) and immediately call istr.unget().  I don't see the point of 
> tellg()/seekg() here because you could not have moved the cursor in the 
> interim.  I commented out these lines and it fixed my test code and 
> adjoints_ex3.  I'm running the rest of the libmesh examples now and will 
> commit if they all pass.
> 
> Would you and Subramanya mind testing apple clang again after I patch getpot 
> and let me know if it works for you? 
> 
> -- 
> John
> 

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