Re: Exception handling Organization: unknown

From:
Alan McKenney <alan_mckenney1@yahoo.com>
Newsgroups:
comp.lang.c++.moderated
Date:
Thu, 1 Oct 2009 02:12:20 CST
Message-ID:
<6ee3d629-c596-48fb-9c26-6da5fdd94c84@h13g2000yqk.googlegroups.com>
On Sep 30, 6:56 am, Goran <goran.pu...@gmail.com> wrote:

On Sep 30, 2:45 am, Zeljko Vrba <mordor.nos...@fly.srk.fer.hr> wrote:

But that's just the point and my greatest annoyance with Java API - most
expected situations (file not found, error while converting int to string,
etc.) have been converted to exceptions. Thus, a simple, readable, short
idiom like

   if(!(f = fopen(...))) ...

suddenly becomes

   try {
     f = WhateverJavaAPI(...);
   } catch(IOException e) {
     ...
   }


I have to repeat what I said before: you seem to be misunderstanding
most basic reason d'?tre for excaptions. (Also: let's not discuss
Java's __checked__ exceptions ;-)). Your code is is much more likely
to be:

try
{
   f = WhateverJavaAPI(...);
   work with f (several operations, all of whom might fail)}

catch(const file_error& e)
{
   crap!

}

Compare to error-return:

if(!(f = fopen(...))) crap!
if (!read(f...)) crap!
if (!read(f...))crap!


    Funny thing about that.

    My most recent experience with exceptions was
    with an API which used exceptions for error
    reporting.

    My code ended up being in the form:

        try { call_1(...); }
        catch ( Except & err )
           { log( "call_1 failed (err %d) %s ... ", ... ); return }
        ...
        try { call_2( ... ); }
        catch ( Except & err )
           { log( "call_2 failed (err %d) %s ... ", ... ); return }

    (Type and function names changed to protect the guilty.)
    That's because the information I want to log depends upon
    which call threw the exception, and the error object doesn't
    say which call it was.

    It would have been easier with error returns.

+ + +

     There are really three situations to be considered
     when talking about how to "use" exceptions:

     1. Where you are writing both the "throw"
         and "catch" code.

     2. Where you are writing the "throw" statements,
         and some other poor fool (in a different company,
         perhaps) has to write the code to catch them.

     3. Where you have to use some library which throws
         exceptions.

     Situation #1 is the easiest to argue about, because
     you can always change what, when, and how is thrown
     and what, when, and how it's caught.

     Situation #2 is the hardest -- if you have any empathy
     for the poor guy/gal who's going to use your code --
     because you don't know the requirements of the code
     that calls your code (if you think you _do_, then
     you're a fool.) My advice is to offer a range of
     options -- e.g., if you want to use exceptions,
     offer a no-throw option, and maybe a call-back
     and/or error return.

     Situation #3 doesn't admit a lot of advice -- you
     play the hand you are dealt, for better or worse.

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