[ITK-dev] Bug in the library, or just in the test..?

[David Cole]

I am sure m_Data is nullptr. In the debugger, it says so. The value of
"this" is a valid pointer, and the value of m_Data is 0x00000000.

The assert is coming from squarely inside a call to std::fill_n with the text:

    Debug Assertion Failed!

    Program: C:\WINDOWS\SYSTEM32\MSVCP120D.dll
    File: C:\Program Files (x86)\Microsoft Visual Studio
        12.0\VC\INCLUDE\xutility
    Line: 2713

    Expression: invalid null pointer

That line is inside std::fill_n, so ... pretty sure m_Data is nullptr.


D




On Fri, Oct 23, 2015 at 1:59 PM, Casey Goodlett <gcasey at gmail.com> wrote:
> Hi David,
>
> I'm not sure that m_Data is nullptr.  I assume its an alias for std::vector
> of size zero.
>
> I've hit this bug a couple of times.  In visual studio debug mode
> &std::vector[0] raises an error for vectors of size zero even if that
> address is never used for anything.  The bug is not in fill_n because the
> error is raised before fill_n is called.  Calling fill_n with a bogus
> pointer and size zero is valid.
>
> On linux the system is happy to generate a bogus pointer thats never used
> for anything so no valgrind errors are ever generated.
>
> I recommend checking an if(m_NumElements >0) in pre c++-11.  In c++11 I
> recommend using the data() method which was added for precisely this reason.
>
> Hope that helps.
>
>
> Casey Goodlett
>
> On Fri, Oct 23, 2015 at 1:47 PM, David Cole via Insight-developers
> <insight-developers at itk.org> wrote:
>>
>> It is definitely related to STL being checked in a Debug Visual Studio
>> build... I get a bunch of ASSERT dialogs that pop up, so the test
>> times out and hangs there with the dialog up until I kill it manually.
>>
>> If I ignore through all the dialogs that pop up (click ignore on each
>> of them, there are exactly 12 in total), then the test output is
>> normal, and it reports that it has PASSED.
>>
>> I can wait for a fix. I was just asking to see if it was a known
>> thing, and find out if anybody was working on it, or if there was a
>> general recommendation about what the right fix for it is before I
>> attempt to fix it myself.
>>
>> I'm curious, though, why is using "&this->m_Data[0]" acceptable if
>> m_Data is nullptr ...? Why doesn't valgrind pick this up as a problem?
>>
>>
>> D
>>
>>
>>
>>
>> On Fri, Oct 23, 2015 at 1:33 PM, Luc Hermitte <luc.hermitte at c-s.fr> wrote:
>> > Hi,
>> >
>> > Le 23/10/2015 18:43, David Cole via Insight-developers a écrit :
>> >> The itkTransformTest is the only test failing on my Visual Studio 2013
>> >> Debug dashboard because of this code:
>> >
>> > What is the exact error produced when your run the test in verbose mode?
>> >
>> >
>> >> The problem is in the Fill implementation:
>> >>
>> >>     template< typename TValue >
>> >>     void VariableLengthVector< TValue >
>> >>     ::Fill(TValue const & v) ITK_NOEXCEPT
>> >>     {
>> >>       std::fill_n(&this->m_Data[0], m_NumElements, v);
>> >>     }
>> >>
>> >> In this test call, m_Data is nullptr, and m_NumElements is 0, so
>> >> clearly,&m_Data[0] is not a useful pointer, and with 0 elements, there
>> >> is nothing to fill.
>> >>
>> >> So.... should the implementation of Fill be changed to be conditional
>> >> on the pointer being non-nullptr, or the number of elements being
>> >> non-zero, or both? (Are other Fill implementations protected like so?)
>> >>
>> >> Or should the test be changed to avoid calling Fill when there are no
>> >> elements...?
>> >
>> > I'd say that this is a bug in std::fill_n (or something related to the
>> > STL being in CHECKED MODE) and that we should fall back into a plain
>> > loop. We should avoid adding such defensive tests (if (!empty)
>> > fill_n()).
>> >
>> > I can take care of this issue (only on Monday). If you don't mind, I'd
>> > rather avoid rebasing yet another time and first go through
>> > http://review.source.kitware.com/#/c/20253/10 (I could also fix the
>> > issue I've introduced in my first patch on VLV in this patch, but this
>> > is not the usual patching policy if I understand correctly)
>> >
>> >
>> > Regards,
>> > --
>> > Luc Hermitte
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