> On Oct 28, 2013, at 2:20 PM, Manav Bhatia <[email protected]> wrote:
>
>
>
>> On Mon, Oct 28, 2013 at 2:53 PM, John Peterson <[email protected]> wrote:
>>
>>
>> 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?
>
>
> The purpose of unget() seems to be to decrease position of istream by one
> character (http://www.cplusplus.com/reference/istream/istream/unget/), so I
> don't see why this would be illegal, unless you are already at the beginning
> of the stream (?).
I'm not sure what actually happens under the hood when you call stream.unget().
Presumably something different than merely stream.seekg(-1, cur) as you seem
to imply.
>> 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.
> Are you sure it is reading the parameters from the input file and not just
> assigning the default values?
>
> Pos is the position of the first character of the parameter. So, if it
> intends to go the beginning of the parameter, then it has to decrease its
> position by one character. For example, if the input parameter is "val", then
> the output of { istr.seekg(Pos); std::cout << "istr" <<std::endl; } would
> be "al", and the output of { istr.seekg(Pos); istr.unget(); std::cout <<
> "istr" <<std::endl; } would be "val".
Note that we are still calling unget(). The only thing I removed was an
(apparently) redundant tellg/seekg pairing...
>> Would you and Subramanya mind testing apple clang again after I patch getpot
>> and let me know if it works for you?
>
>
> I will be glad to test.
>
> -Manav
>
>
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