Re: Which exception for a buffer overrun?

From	David Brown <david.brown@hesbynett.no>
Newsgroups	comp.lang.c++
Subject	Re: Which exception for a buffer overrun?
Date	2019-10-16 23:00 +0200
Organization	A noiseless patient Spider
Message-ID	<qo80dd$pn6$1@dont-email.me> (permalink)
References	(2 earlier) <4aaa75f3-a489-49bd-89cf-356ece235d21@googlegroups.com> <qo4c7f$smj$1@dont-email.me> <qo5ffc$fpe$1@dont-email.me> <qo6jls$hog$1@dont-email.me> <h0p8ijF41nU1@mid.individual.net>

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On 16/10/2019 21:15, Ian Collins wrote:
> On 16/10/2019 21:16, David Brown wrote:

>> Readability is of course very important - and code correctness even more
>> so.  However, I am not convinced that exceptions are a great correctness
>> feature.  It is hard to write fully exception-safe code.  And, worse, it
>> is easy to write code that /appears/ to be exception safe, but is not.
>>
>> The two key problems, as I see it, are first that exceptions means all
>> sorts of code (function calls and expressions) can fail unexpectedly at
>> any time, leading to early returns from your function.  You have to be
>> thinking all the time about what will happen if there is an exception
>> when the code runs.  This can mean making more RAII classes, or more
>> indirect references (via unique_ptr, for example), simply to ensure
>> cleanup in case functions throw an exception.  That will make the code
>> safe and correct - but can be of significant readability cost.
> 
> The same set of conditions also apply to code that uses early returns. 
> Throwing an exception is just a special case of an early return.

There are two big differences.  One is that with an early return, 
everything is clear in the code - you know /exactly/ when the return 
happens, without having to consider whether functions may or may not 
throw.  The second is that you have control of the return - you can 
choose if it is early, or if other things are done first.

> 
>> The other problem is that a lot of the information about C++ exceptions
>> that a function can throw, is basically lying.  You can /say/ that a
>> function only throws specific exception types, which would be very
>> useful, but it's a lie.  At least C++11 "noexcept" is a stronger, and
>> now "throw" specifications are no longer part of C++17 at all.  But
>> there is currently no way to say what exceptions a function really could
>> throw, no way to check such features at compile time, no integration
>> with the type system, and the default is for functions to be specified
>> as "this function could throw anything, or pass on any exception" rather
>> than the more sensible "this function won't throw - it will do what it
>> says it will do".
> 
> This is true, but we are already there when we use the standard library 
> unless we build with exceptions disabled.
> 

Correct me if I am wrong, but for the most part the only exception that 
will be thrown by the standard library is for failed memory allocations. 
  On many platforms, it is highly unlikely ever to happen - and for many 
programs, the situation is so unexpected and critical that a dead crash 
and error message is probably an acceptable way to handle it.

Thread

Which exception for a buffer overrun? Frederick Gotham <cauldwell.thomas@gmail.com> - 2019-10-15 03:00 -0700
  Re:Which exception for a buffer overrun? melzzzzz <mel@melzzzzz.com> - 2019-10-15 12:52 +0200
    Re: Re:Which exception for a buffer overrun? queequeg@trust.no1 (Queequeg) - 2019-10-16 12:52 +0000
      Re: Re:Which exception for a buffer overrun? melzzzzz <mel@melzzzzz.com> - 2019-10-16 18:29 +0200
  Re: Which exception for a buffer overrun? Paavo Helde <myfirstname@osa.pri.ee> - 2019-10-15 13:54 +0300
    Re: Which exception for a buffer overrun? Frederick Gotham <cauldwell.thomas@gmail.com> - 2019-10-15 04:08 -0700
      Re: Which exception for a buffer overrun? David Brown <david.brown@hesbynett.no> - 2019-10-15 13:57 +0200
        Re: Which exception for a buffer overrun? Soviet_Mario <SovietMario@CCCP.MIR> - 2019-10-15 23:59 +0200
          Re: Which exception for a buffer overrun? scott@slp53.sl.home (Scott Lurndal) - 2019-10-15 22:13 +0000
            Re: Which exception for a buffer overrun? Soviet_Mario <SovietMario@CCCP.MIR> - 2019-10-16 15:04 +0200
          Re: Which exception for a buffer overrun? Paavo Helde <myfirstname@osa.pri.ee> - 2019-10-16 07:57 +0300
            Re: Which exception for a buffer overrun? Soviet_Mario <SovietMario@CCCP.MIR> - 2019-10-16 15:05 +0200
            Re: Which exception for a buffer overrun? Keith Thompson <kst-u@mib.org> - 2019-10-16 15:34 -0700
          Re: Which exception for a buffer overrun? David Brown <david.brown@hesbynett.no> - 2019-10-16 10:16 +0200
            Re: Which exception for a buffer overrun? Öö Tiib <ootiib@hot.ee> - 2019-10-16 05:54 -0700
              Re: Which exception for a buffer overrun? David Brown <david.brown@hesbynett.no> - 2019-10-16 16:12 +0200
                Re: Which exception for a buffer overrun? Soviet_Mario <SovietMario@CCCP.MIR> - 2019-10-16 20:45 +0200
                Re: Which exception for a buffer overrun? Öö Tiib <ootiib@hot.ee> - 2019-10-17 06:34 -0700
                Re: Which exception for a buffer overrun? David Brown <david.brown@hesbynett.no> - 2019-10-17 16:34 +0200
            Re: Which exception for a buffer overrun? Ian Collins <ian-news@hotmail.com> - 2019-10-17 08:15 +1300
              Re: Which exception for a buffer overrun? David Brown <david.brown@hesbynett.no> - 2019-10-16 23:00 +0200
                Re: Which exception for a buffer overrun? Ian Collins <ian-news@hotmail.com> - 2019-10-17 10:36 +1300
                Re: Which exception for a buffer overrun? David Brown <david.brown@hesbynett.no> - 2019-10-17 10:14 +0200
                Re: Which exception for a buffer overrun? Daniel <danielaparker@gmail.com> - 2019-10-16 20:06 -0700
            Re: Which exception for a buffer overrun? Bonita Montero <Bonita.Montero@gmail.com> - 2019-10-18 09:45 +0200
        Re: Which exception for a buffer overrun? Bonita Montero <Bonita.Montero@gmail.com> - 2019-10-17 21:22 +0200
      Re: Which exception for a buffer overrun? Paavo Helde <myfirstname@osa.pri.ee> - 2019-10-15 17:48 +0300
    Re: Which exception for a buffer overrun? "Fred. Zwarts" <F.Zwarts@KVI.nl> - 2019-10-15 13:09 +0200
      Re: Which exception for a buffer overrun? David Brown <david.brown@hesbynett.no> - 2019-10-15 13:35 +0200
        Re: Which exception for a buffer overrun? scott@slp53.sl.home (Scott Lurndal) - 2019-10-15 13:30 +0000
      Re: Which exception for a buffer overrun? melzzzzz <mel@melzzzzz.com> - 2019-10-15 13:49 +0200
        Re: Which exception for a buffer overrun? David Brown <david.brown@hesbynett.no> - 2019-10-15 13:59 +0200
      Re: Which exception for a buffer overrun? Jorgen Grahn <grahn+nntp@snipabacken.se> - 2019-10-15 14:48 +0000
        Re: Which exception for a buffer overrun? Paavo Helde <myfirstname@osa.pri.ee> - 2019-10-15 18:37 +0300
          Re: Which exception for a buffer overrun? melzzzzz <mel@melzzzzz.com> - 2019-10-15 18:48 +0200
      Re: Which exception for a buffer overrun? queequeg@trust.no1 (Queequeg) - 2019-10-16 13:00 +0000
    Re: Which exception for a buffer overrun? Mr Flibble <flibbleREMOVETHISBIT@i42.co.uk> - 2019-10-15 18:21 +0100
      Re: Which exception for a buffer overrun? Melzzzzz <Melzzzzz@zzzzz.com> - 2019-10-15 20:32 +0000
        Re: Which exception for a buffer overrun? Jorgen Grahn <grahn+nntp@snipabacken.se> - 2019-10-16 06:20 +0000
    Re: Which exception for a buffer overrun? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2019-10-16 14:43 -0700
  Re: Which exception for a buffer overrun? Jorgen Grahn <grahn+nntp@snipabacken.se> - 2019-10-15 11:12 +0000
  Re: Which exception for a buffer overrun? Öö Tiib <ootiib@hot.ee> - 2019-10-15 13:44 -0700
    Re: Which exception for a buffer overrun? Mr Flibble <flibbleREMOVETHISBIT@i42.co.uk> - 2019-10-15 22:43 +0100
      Re: Which exception for a buffer overrun? Öö Tiib <ootiib@hot.ee> - 2019-10-16 00:01 -0700
        Re: Which exception for a buffer overrun? Jorgen Grahn <grahn+nntp@snipabacken.se> - 2019-10-16 19:02 +0000
          Re: Which exception for a buffer overrun? Öö Tiib <ootiib@hot.ee> - 2019-10-16 15:22 -0700
            Re: Which exception for a buffer overrun? Mike Terry <news.dead.person.stones@darjeeling.plus.com> - 2019-10-17 03:31 +0100
              Re: Which exception for a buffer overrun? Ian Collins <ian-news@hotmail.com> - 2019-10-17 15:35 +1300
                Re: Which exception for a buffer overrun? David Brown <david.brown@hesbynett.no> - 2019-10-17 10:17 +0200
            Re: Which exception for a buffer overrun? Jorgen Grahn <grahn+nntp@snipabacken.se> - 2019-10-20 22:18 +0000
              Re: Which exception for a buffer overrun? Öö Tiib <ootiib@hot.ee> - 2019-10-21 04:06 -0700

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