Re: debug/vector anomalous behaviour

[Roberto Bagnara <bagnara at cs dot unipr dot it>]

Doug Gregor wrote:
> On Sat, May 10, 2008 at 7:21 AM, Stefano Soffia <soffia@cs.unipr.it> wrote:
> > On Sat, 10 May 2008, Paolo Carlini wrote:
> > > However, I'm puzzled by the default, which uses the _M_guaranteed_capacity
> > > idea, trying to flag potentially dangerous situations. Now that I look a bit
> > > into it, frankly I'm not sure it's worth such kind of false positives...
> > > Maybe Doug (the author of these bits, a long time ago, if I remember
> > > correctly...), wants to clarify the rationale.
> > I have spoken about this with my colleagues Enea Zaffanella and Roberto
> > Bagnara and our guess is that the intended meaning for the pedantic mode is
> > to provide the user with the minimal capacity() necessary satisfy the
> > requirements of the C++ Standard (for example, this would mean that when a
> > push_back() requires a reallocation, instead of doubling the current
> > capacity(), the capacity is increased only by 1.)
> > While the non-pedantic behaviour simply provides the capacity of the
> > underlying implementation, allowing the user to make assumptions about
> > implementation-defined aspects of the standard.
>
> Yes, this was exactly my intent. The standard doesn't say how the
> capacity rows, so _M_guaranteed_capacity mimics the slowest-growing
> vector possible while this->capacity() is how libstdc++ actually grows
> the vector. It's under the pedantic mode because nearly every standard
> library implementation grows a vector the same way.

So

  365 #ifdef _GLIBCXX_DEBUG_PEDANTIC
  366         return __elements > this->capacity();
  367 #else
  368         return __elements > _M_guaranteed_capacity;
  369 #endif

should become

  365 #ifndef _GLIBCXX_DEBUG_PEDANTIC
  366         return __elements > this->capacity();
  367 #else
  368         return __elements > _M_guaranteed_capacity;
  369 #endif

right?

All the best,

   Roberto

--
Prof. Roberto Bagnara
Computer Science Group
Department of Mathematics, University of Parma, Italy
http://www.cs.unipr.it/~bagnara/
mailto:bagnara@cs.unipr.it