Re: Is there any standard/guarantees for exception safety in STL operations?

"Bo Persson" <>
Sat, 31 Jul 2010 08:36:49 CST
Dragan Milenkovic wrote:

On 07/30/2010 08:54 PM, Bo Persson wrote:

Dragan Milenkovic wrote:


This I agree. I do feel uneasy, like there is a hole in
the specification of std::vector. Me likes things clean
and strictly defined, yes. Maybe, they should have just
banned objects that throw on copy/move.

But they didn't want to do that, just because some type can throw
once in a million years.

Sorry, I didn't understand this. I hope you are not describing
a class whose ctor can throw only rarely... A type can either
throw or it can not; chances and probability must be excluded
from the logic. But I'm pretty sure this is not what you meant...

I did actually. :-)

There are classes that can throw, but you might know in advance that
it isn't going to happen today. If might throw for lack of resources,
but I know that there are plenty of those resources right now. Then it
would be safe to use the class anyway.

For an extreme example, say that you have a class that throws an
exception, but only on February 29th, if it is a Thursday with a lunar
eclipse. Now I know that today it is around July or August in a year
that isn't divisible by 4.

Should the standard say that I cannot put my class in a std::vector,
because it throws exceptions? The library designers chose not to do
that, leaving it up to me. Can I live with the effects, or can I tell
that nothing bad will happen right now?

I agree that the standard isn't a tutorial, but often a rather dry
statement of facts. To avoid repetitions, and the risk of
contradictions with that, it sometimes only states a certain rule in
one place, where it is first needed. Occationally it is not obvious
where that place is, but that's how it is.

The 1300 pages of the current draft doesn't exacly encourage adding
more explanations either. :-)

Bo Persson

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