Re: [boost] Preliminary Review Request: boost-memory

From: shiwei xu (xushiweizh_at_[hidden])
Date: 2008-05-07 00:04:37

You're right. I'm mistaken. :)

On Wed, May 7, 2008 at 11:11 AM, Scott McMurray
<me22.ca+boost_at_[hidden]<me22.ca%2Bboost_at_[hidden]>>
wrote:

> On Tue, May 6, 2008 at 10:47 PM, shiwei xu <xushiweizh_at_[hidden]> wrote:
> > Your question is very interesting. I thought it before. In fact I don't
> know
> >  a perfect solution. If the constructor of an object throws, should the
> >  destructor be called?
> >
> >  class Foo
> >  {
> >  private:
> >     A m_a;
> >     B m_b;
> >     C m_c;
> >
> >  public:
> >     Foo() {
> >         m_a.init();
> >         m_b.init();
> >         thow std::exception("error");
> >         m_c.init();
> >     }
> >     ~Foo() {
> >         ...
> >     }
> >  };
> >
> >  Suppose we initialized m_a and m_b. m_c was uninitialized when the
> exception
> >  throws. If the destructor is called, it may cause a crash. If the
> destructor
> >  isn't called, the allocated memory of m_a and m_b will be leaked.
> >
> >  I choose to call the destructor because I think that a crash is easy to
> be
> >  detected and be solved.
> >
>
> This is a non-point.  Go read the rules for which destructors are
> called when exceptions are thrown in different places.  If A and B are
> written properly, there's no problem.  And in any case, throwing in a
> constructor for an automatic variable doesn't call the destructor, so
> no matter what you think, you shouldn't call the destructor, since
> it'll break expectations.
>
> Here's a simple counter-example:
> int *bar() {
>    throw 0;
>    return new int(42);
> }
> struct foo {
>    int *p;
>    foo() : p(bar()) {}
>    ~foo() { delete p; }
> };
>
> Quite obviously UB to call that destructor.
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