Re: Memory issue

James Kanze <>
Tue, 11 Aug 2009 03:08:27 -0700 (PDT)
On Aug 10, 10:10 pm, Andy Champ <no....@nospam.invalid> wrote:

Alf P. Steinbach wrote:

In that case, the C++ standard guarantees a std::bad_alloc
exception as the default response, provided the allocation
at the bottom was via 'new'.

.. but be aware that (at least some of) the Microsoft compilers are
defective in this area, returning NULL instead of an exception.

Be aware that a lot of compilers or systems have problems in
this regard. By default, for example, Linux will calmly tell
the system it has the memory, then cause the program to core
dump when it tried to use it. Some versions or configurations
of AIX or HP/UX also have this problem. And on at least one
configuration of Windows that I tried (NT, a long time ago),
when there wasn't enough memory, the system popped up a dialog
box asking you to kill other processes so it could retry;
operator new didn't return until you clicked on the dialog.

At any rate, the current Microsoft compilers (from Visual Studio
8) don't seem to have this problem. I also couldn't create
Alf's problem with my small tests. I was able to allocate 1917
blocks of 1MB, touching one byte every 1024 in each block in
order to be sure that it was really allocated, and I got a
bad_alloc, with no apparent thrashing or or any other bad
effects. (I'm afraid I don't know the exact configuration.
It's just a machine on my desk, which I normally only use for

A lot depends on how the OS manages its swap space, if there
isn't sufficient real memory. I remember doing the same test
under Solaris 2.2---the system literally hung for about 10
minutes... before I got a null pointer and could free the
memory. Solaris 2.4 was already a lot better, and while it
would thrash considerably (this was with 48MB real memory, and a
swap space of maybe 100 GB), the mouse would still react, and
you could use an xterm, albeit slowly.

James Kanze (GABI Software)
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