Re: Exception Safe Guard

From:

Barry <dhb2000@gmail.com>

Newsgroups:

comp.lang.c++

Date:

Wed, 05 Sep 2007 17:28:10 +0800

Message-ID:

<fblsrc$i71$1@aioe.org>

Michael DOUBEZ wrote:

Yes and if you want to demonstrate guard idiom, you should definitly not
use catch(...) otherwise the following code is enough:
Obj obj;
try
{
// do the stuffs, which may throw
MayThrow();
}
catch (int i)
{
//...
}
catch(..)
{
//...
}
obj.Rollback()

Here catch(...) allows a 'finaly like' system which is not the point.

Michael,
you miss the most important part here.
Maybe I should've written the code in this may to make it clearer

void Transact() throw(int)
{
         Obj obj;
         Guard guard(bind(&Obj::Rollback, obj));

         // do the stuffs, which may throw
         MayThrow();

         // coming this far, nothing thrown, we commit the transaction
         guard.Commit();
         cout << "Transaction successful" << endl;

         // no matter exception thrown or not
         // guard will be destructed, ~Guard() will be called

         // 1. if exception throw then committed_ must be false
         // the roll back functor will be called
         // 2. else roll back functor won't be called, as
         // committed_ is true
}

int main()
{
    try
    {
       Transact();
    }
    catch (int i)
    {
    }
}

--
Thanks
Barry