Question about compiler bug: Value-initialization in new-expression

From:

"Niels Dekker - no return address" <unknown@this.is.invalid>

Newsgroups:

microsoft.public.vc.language

Date:

Mon, 14 May 2007 21:41:58 +0200

Message-ID:

<OCRui$llHHA.1340@TK2MSFTNGP04.phx.gbl>

I recently got into trouble because MSVC++ appeared to incorrectly
implement value-initialization, for a struct that I was using. Luckily
the bug was reported in 2005 already, by Pavel: Feedback ID 100744,
"Value-initialization in new-expression".
https://connect.microsoft.com/VisualStudio/feedback/ViewFeedback.aspx?FeedbackID=100744

The example has a struct that looks very much like mine:

  struct A {
    std::string s;
    int i;
  };

When doing "new A()", the int data member does not get zero-initialized,
as it should. Jonathan Caves (Visual C++ Compiler Team) has admitted
that it is indeed a bug.

Note that other attempts to value-initialize the struct fail as well:

  #include <cassert>

  class B {
    A m_a;
  public:
    B(): m_a() {
      assert(m_a.i == 0); // Assertion fails!
    }
  };

  int main() {
    A a1 = A();
    assert(a1.i == 0); // Assertion fails!
    A a2((A()));
    assert(a2.i == 0); // Assertion fails!
    B b;
    return a1.i + a2.i;
  }

This is a serious bug! Is it going to be solved with the next service
packs of VC++ 2003 and VC++ 2005? According to the Feedback page, the
status of #100744 is "Closed (Won't Fix)". Does that really mean that
this bug won't get fixed at all???

Kind regards,
--
Niels Dekker
http://www.xs4all.nl/~nd/dekkerware
Scientific programmer at LKEB, Leiden University Medical Center