Re: is such exception handling approach good?

From:

"Ben Voigt [C++ MVP]" <rbv@nospam.nospam>

Newsgroups:

microsoft.public.vc.language

Date:

Thu, 27 Dec 2007 09:14:56 -0600

Message-ID:

<exSrPsJSIHA.1208@TK2MSFTNGP03.phx.gbl>

"George" <George@discussions.microsoft.com> wrote in message
news:D6324B3F-D9FF-44A8-BA57-F5F19F5DEF8E@microsoft.com...

Hi Ben,

I do not quite agree.

oops, it can't either.

http://www.gotw.ca/gotw/066.htm

which statements do you mean in this article mentioned we can not use
try
and catch block in constructor to free resources if there are any
exceptions
in constructor? I can not find. And it is appreciated if you could
point
out.

A function-try block is different from a try block inside the function.

suppose we have a class which has a member variable int*, and in
constructor
we have succeed in allocating memory and assign the int* to the memory
block.

Then in some other code in the constructor, there are exception. Then we
can
in the exception handler block of constructor. I think in the handler, we
should free the memory using delete or delete[], then re-throw the
exception.
Is it good code? Any potential issues?

You cannot use a function-try block for that, the member variable is
inaccessible.

You could use a try/catch inside the constructor body, but it will not catch
exceptions thrown from base and member constructors.

And a function-try block is different from a try block inside the function.
They are described by two different clauses in the C++ standard.

regards,
George

"Ben Voigt [C++ MVP]" wrote:

"George" <George@discussions.microsoft.com> wrote in message
news:19D2BF33-C57C-4FB8-88E5-24BBAD9E9D0D@microsoft.com...

Hi Ben,

oops, it can't either.

http://www.gotw.ca/gotw/066.htm

A function-try block is different from a try block inside the function.

:-)

regards,
George

"Ben Voigt [C++ MVP]" wrote:

"Ben Voigt [C++ MVP]" <rbv@nospam.nospam> wrote in message
news:ebuG5vlRIHA.4400@TK2MSFTNGP06.phx.gbl...

"George" <George@discussions.microsoft.com> wrote in message
news:0751E682-FEF6-4EEF-8BD0-A8B30818973A@microsoft.com...

Thanks Alex,

Unless the caller of the constructor catches the exceptions and
take
appropriate operations to free the resources/memory, right?

Do you mean author of the constructor? Caller of the constructor
is a code that creates an object.

I mean the caller of the constructor. If the caller can catch the
exception
in the constructor, and take appropriate operations to free
resources,
I
think it is fine to throw exceptions in constructor. Is my
understanding
correct?

The caller of the constructor cannot free the resources, because he
hasn't
got a pointer to them (constructor failed and the pointer to the new
object was never set).

Only a function-try block on the constructor can free the resources.

oops, it can't either.

http://www.gotw.ca/gotw/066.htm

regards,
George

"Alex Blekhman" wrote:

"George" wrote:

I think if you are not using smart pointers, for the object
instances which
are already constructed on the heap, they will not be released
automatically
and there will be potential memory leak, right?

Correct.

Unless the caller of the constructor catches the exceptions and
take
appropriate operations to free the resources/memory, right?

Do you mean author of the constructor? Caller of the constructor
is a code that creates an object.

Alex