On Jun 29, 12:41pm, Erik Wikström <Erik-wikst...@telia.com> wrote:
> On 2008-06-29 17:34, Vijay wrote:
>
>
>
> > Hi All,
>
> > I am not able to figure out what exactly happening in below code. what
> > is control flow. Can anyone clear my confusion?
>
> > Code:
> > class A
> > {
> > public:
> > A(){cout<<"In Constructor\n";}
> > //// A(const A&){cout<<"In Copy Constructor\n";} // if we uncomment
> > this, we see different //output .
> > ~A(){cout<<"In Destructor\n";}
> > };
> > try{
> > cout<<"In Try\n";
> > throw A();
> > }
> > catch(A &a)
> > {
> > cout<<"In Catch\n";
> > }
> > output:
> > In Try;
> > In Constructor
> > In Destructor
> > In Catch
> > In Destructor
>
> > Question 1. I don't know why two times destructor has been called. I
> > understand, since i am using reference, so there would not be any new
> > object. then why two times destructor got called.
>
> The throw-expression creates a temporary object (the exception object)
> using the copy-constructor and that is the one destroyed after the
> handler has run. The compiler is however allowed to optimise away the
> extra object, what is funny is that my compiler chooses to do so only
> when I uncomment the copy-constructor.

yes. even i was thinking same. but was confused why compiler shows
different behavior after uncommenting the copy constructor. Thanks for
you reply


>
> > Question 2.
>
> > class A
> > {
> > public:
> > A(){cout<<"In Constructor\n";}
> > A(const A&){cout<<"In Copy Constructor\n";}
> > ~A(){cout<<"In Destructor\n";}
> > };
> > try{
> > cout<<"In Try\n";
> > throw A();
> > }
> > catch(A a)
> > {
> > cout<<"In Catch\n";
> > }
> > output:
> > In Try;
> > In Constructor
> > In Copy Constructor
> > In Catch
> > In Destructor
> > In Destructor
>
> > Why object created by throw A() has not been deleted while exiting try
> > block in above code?
>
> The object created by thow can not be destroyes before it has been used
> to initialise the object in the exception-handler (the extra copy has
> been eliminated). It will also live until the last exception handler has
> run (if the object is destroyed and you re-throw what would happen
> then?), so it is the last destructor to run.
>
> If I comment out the copy-constructor my compiler does not optimise away
> the extra copy and I get the following result:
>
> In Try
> In Constructor // throw A(), followed by a copy-constructor
> In Destructor // The object created by A() is destroyed
> In Catch // a in the catch(A a) is copy-constructed first
> In Destructor // The object created in the handler is destroyes
> In Destructor // The exception object dies

Thanks. I think, because of compiler optimization, i am getting
confused.
one more point: in your above result, i didnt get two lines
In Destructor // The object created by A() is destroyed
and
In Destructor // The exception object dies

object created by A() is exception object. right?
If no, then when exception object is created which dies in last line?

Thanks a lot
>
> --
> Erik Wikström