Re: Testing Program Question

From:

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

Newsgroups:

comp.lang.c++

Date:

Tue, 16 Feb 2010 13:10:10 +0100

Message-ID:

<hle22u$1sd$1@news.eternal-september.org>

* Nick Keighley:

On 16 Feb, 01:20, "Alf P. Steinbach" <al...@start.no> wrote:

* Alf P. Steinbach:

the reason that I've never used the alloca technique that I mention above seems
to be that alloca *is not* consistently defined on different platforms.

   <url:http://www.mkssoftware.com/docs/man3/alloca.3.asp>
   guarantees 0 on error,

   <url:http://msdn.microsoft.com/en-us/library/wb1s57t5%28VS.71%29.aspx>
   guarantees a "stack overflow exception" on error, and

   <url:http://www.kernel.org/doc/man-pages/online/pages/man3/alloca.3.html>
   says the error behavior is undefined.

Perhaps the group can benefit from this info.

I understand it doesn't "play well" with C99's vararray.

Didn't know that but it stands to reason; they compete for the same resource.

How well does it interact with new/delete?

I can't see any reason why the features should interact in any way. alloca
adjusts the stack pointer. new/delete allocate from some heap.

At least in Windows programming a major usage of alloca is to allocate strings
efficiently for conversion between char strings and wchar_t strings.

And there's no problem with that, when used correctly, but alloca is a very
fragile low-level mechanism.

Cheers,

- Alf