Re: Necessity of multi-level error propogation

From:

"Alf P. Steinbach" <alfps@start.no>

Newsgroups:

comp.lang.c++

Date:

Fri, 13 Mar 2009 16:41:04 +0100

Message-ID:

<gpduqg$sf6$1@news.motzarella.org>

* Jeff Schwab:

Alf P. Steinbach wrote:

* Jeff Schwab:

James Kanze wrote:

On Mar 12, 10:57 am, Jeff Schwab <j...@schwabcenter.com> wrote:

James Kanze wrote:

On Mar 11, 7:54 pm, peter koch <peter.koch.lar...@gmail.com> wrote:

The only know alternative to exceptions is return codes

For a very liberal meaning of "return code". You can use
out parameters, global variables (ever heard of errno?)

errno isn't a global variable, it's a macro. On the system
I'm using to post this message, it maps to a function call.

I was talking about the concept, not the actual implementation.
According to the C standard, errno is a "symbol" which expands
to a modifiable lvalue. (It may be a macro, or an indentifier.)
Historically, it was usually a global variable, and earlier
versions of Posix required that. A global variable doesn't work
very well in a multithreaded environment, however; I'm pretty
sure that Posix requires that it be distinct for each thread.
In the end, though, it is still a global variable, although
normally a thread local one.

That's like saying a function is a global variable, just because it
accesses one. errno is a macro, period, with all the attendant
problems that macros cause. See my reply elsethread.

Somewhere else-thread someone quoted from C90 standard, "... value of
the macro EDOM is stored in errno".

Explain how you store a value in a macro.

In C90, errno doesn't have to be a macro. In C++, it does.

Yes that's right.

But please answer the question instead of trying to evade it.

For C++, how do you store a value in a macro.

Thanks in advance,

- Alf

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