Re: [Boost-Users] Signals lib - causes mysterious multiple destructor calls

From: William E. Kempf (wekempf_at_[hidden])
Date: 2003-05-16 17:28:56

Chuck Messenger said:
> Testing out the Boost signals lib, I wrote:
>
> -----------
> #include <boost/signal.hpp>
> #include <iostream>
>
> using namespace std;
> using namespace boost;
>
> struct X {
>      void operator()(int val) { cout << "X <- " << val << endl; }
>      X() { cout << "X constructor\n"; }
>      ~X() { cout << "X destructor\n"; }
> };
>
>
> int main() {
>      {
>          cout << "   phase 1\n";
>          signal<void (int)> sig;
>          cout << "   phase 2\n";
>          X x;
>          cout << "   phase 3\n";
>          sig.connect(x);
>          cout << "   phase 4\n";
>      }
>      cout << "   phase 5\n";
>
>      return 0;
> }
> -------------------
>
> The following output is generated (gcc3.2.2 on Mandrake 9.1):
>
> ------------------------
>     phase 1
>     phase 2
> X constructor
>     phase 3
> X destructor
> X destructor
> X destructor
> X destructor
> X destructor
> X destructor
> X destructor
> X destructor
>     phase 4
> X destructor
> X destructor
>     phase 5
> ------------------------
>
> Why the multiple calls to X's destructor?  I'd have expected just one.
> It looks like the signals lib is misbehaving.

No, it's not.  X is being destructed as many times as it's being
constructed.  What's missing to help you see this is a user defined copy
constructor for X.

-- 
William E. Kempf