exceptions and ctor initializers

[Ken Teh <kmt at slowpoke dot phy dot anl dot gov>]

I'm using C++ exceptions in egcs-1.1b on a i586-pc-linux-gnulibc1 box.  I am
confused by its behaviour when it comes to throwing exceptions in a ctor
initializer list.  It doesn't jive with what I've read in Stroustrup's 3rd
edition.  Can someone please clarify?

I am trying to put together a simple traceback using exceptions.  First, I
define my exception class as follows:

	class X {
	    string _what;
	public:
	    X(const string& what_arg) : _what(what_arg) {}
	    virtual const char * what () const { return _what.c_str(); }
	    virtual void append(const string& a) { _what.append(a); }
	};

The base and derived classes look like:

	class B {
	public:
	    B() throw(X);
	    virtual ~B() throw() {}
	};

	B::B() throw(X) {
	    char m[80];
	    sprintf(m, "\n%31s:%-8d", __FILE__, __LINE__);
	    throw X(m);
	}

	class D : public B {
	public:
	    D() throw(X);
	    ~D() throw() {}
	};

	D::D() throw(X)
	try : B()
	{
	    // do D initialization
	}
	catch (X& x) {
	    char m[80];
	    sprintf(m, "\n%31s:%-8d", __FILE__, __LINE__);
	    x.append(m);
	    throw;
	}

	int main()
	{
	    try { D d; }
	    catch (X &x) {
		fprintf(stderr, "%s\n", x.what());
	    }
	}

When I run this, I expect to see a simple traceback of the exceptions
thrown, that is, 2 lines of traceback showing each point at which the
exception was thrown (and rethrown).

I don't.  I see only one line and that's the line thrown by B's constructor.
The D constructor catch block is not invoked. Why?  There is no real
concern; I still have sufficient information on hand, and if the stack
unwind cleans up properly, then all is well.  But, I'm still confused.