Re: try and catch

"Alf P. Steinbach" <>
Tue, 27 Feb 2007 05:15:50 +0100
* Gary Wessle:


I am using exceptions in my code and not sure how things are suppose
to work in my case.

while (1){
      // call some methods here and use their side effect and returns.
      catch ( catch'm )
      // something wicked happened.

Is this ok?

Well, it's a well-known pattern, but at the lowest possible level of

Note: if you don't use a counter or other loop variant, you risk an
infinite loop.

Also, to avoid silly-warnings from some compilers, better write
'for(;;)' than 'while(1)', even if the latter is an old C idiom.

I mean, I keep on trying to do the task and break once it is done or
handle the error and get back to the same task again in case a throw

Yeah, OK.

But if you have that low-level pattern occurring more than one place in
your code, consider abstracting it using the template pattern (nothing
to do with templates), like

   const unsigned untilDoomsday = unsigned(-1);

   struct Retry
       bool operator( unsigned maxTries ) const
           while( maxTries > 0 )
                   return true;
               catch( std::exception const& x )
                   onException( x );
               if( maxTries != untilDoomsday ) { --maxTries; }
           return false;

       virtual void doIt() const = 0;
       virtual void onException( std::exception const& x ) const {}

   const bool succeeded = RetryDangerousThing()( untilDoomsday );

IIRC this was John Harrison's idea (not his code though, the above is
just scribbled down, guaranteed untouched by compiler's hands).

A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
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