Re: What should function returning a reference return on failure?

"Jim Langston" <>
Mon, 8 May 2006 09:10:20 -0700
"Jim Langston" <> wrote in message

"Alf P. Steinbach" <> wrote in message

* Jim Langston:

I'm sure this has been asked a few times, but I'm still not sure.

If the function returns a reference, it's guaranteeing that if it
returns, the result is a valid reference.

You have the choice of using (1) a reference to some special object
denoting "no object" or "failure", or (2) throwing an exception.

(2) is most clean, most reliable wrt. client code checking, and may help
avoid constructing a large dummy object.

Dang, there's one problem with the try...catch.

  CMap& ThisMap = FindMap( MapNumber );
catch ( int )
  LogError("Could not find map");

That ThisMap is only going to exist during the lifetime of the try block.
And I can't create it outside the block because it's a reference and has
to be initialized.

Now this means I'll have to put whole blocks of code inside the try block,
but I don't want to catch errors in a block for all the code, and a lot of
the code should execute anyway even if they can't find the map.

That is, this code won't compile:

   int i = 1;
       int& j = i;
   catch (...)

   std::cout << j << std::endl;

I finally settled on this (ugly) code:

// Get a reference in the map for this player
   CPlayer& ThisPlayer = FindPlayer( Socket );
catch ( int )
   SendMessageToPlayer( Socket, MSG_SERVER_MESSAGE, "<Message not sent,
please relog - Error has been logged>" );
   MessageBuffer.push_back( LogError( "Unlogged in client attempting to send
message on socket " + StrmConvert<std::string>( Socket ) + " on IP " +
IP ) );
   return 0;
CPlayer& ThisPlayer = FindPlayer( Socket );

My feeling being that if it doesn't throw on the first call to FindPlayer
it's not going to throw on the second call to FindPlayer and I can proceed.
If it does throw on the second call somehow then it's an actual program
error and the program can halt on an uncaught error.

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