l i n u x - u s e r s - g r o u p - o f - d a v i s
Next Meeting:
July 7: Social gathering
Next Installfest:
Latest News:
Jun. 14: June LUGOD meeting cancelled
Page last updated:
2002 Jul 16 21:50

The following is an archive of a post made to our 'vox-tech mailing list' by one of its subscribers.

Report this post as spam:

(Enter your email address)
[vox-tech] dyanamic memory panacea
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

[vox-tech] dyanamic memory panacea

Peter Jay Salzman writes:
 > ok, not a panacea, but pretty cool nevertheless...
 > i was doing some reading and found a function alloca() which allocates
 > dynamic memory like malloc() and friends, but it gets memory from the
 > current stack frame instead of the heap.
 > the obvious advantage is that the memory is deallocated once the stack
 > frame is popped.  in other words, when the function returns, all memory
 > allocated by alloca is freed.  this means no memory leaks.  very cool.
 > however, in the man page, under BUGS, it says:
 >        The alloca function is machine dependent.
 > this doesn't say anything to me.  what does it mean for a function to be
 > machine dependent?   does it behave differently across different
 > machine architectures?  does code compiled on one x86 machine not run on
 > another x86 machine?
 > what exactly is the man page warning me about?

Jeff gave the appropriate answer here; however, it's worth pointing
out that alloca() is not standard - either to C or POSIX (or any other
standard to my knowledge); so there's no guarantee you can use it in
other environments. In practice, it is a fairly common UNIX extension,

The latest C standard (C99) has addressed most of the uses which make
alloca() convenient through the use of "compound literals". This
facility allows you to specify a struct or array literal, which is
freed when it goes out of scope. It has been supported (though not
fully) for some time in GCC; you can read about it in GCC's info page,
under C Extensions: Compound Literals.

However, there is only one implementation currently in existence that
supports the C99 standard - and GCC isn't it (still a rather far cry
from compliance, actually). So, using this construct isn't portable
across a variety of other platforms, either. However, there is at
least the fact that it is in the C standard, and will be implemented
in all modern C implementations at some time in the near future -
alloca() still shows no signs of standardization (e.g., it's not in
the current POSIX draft).

For my part, I don't use either one, until more conformant C99
implementations are abundant.

If you're curious, the one conformant C99 implementation is available
on Linux. It is not Free, however - either as in beer or speech. I
don't own it, but have a good deal of respect for the developer, and
have often considered it. Also, the web site gives you a free trial
run of their software - only checks for syntax errors, though: it
won't actually compile or run software.


vox-tech mailing list

LUGOD Group on LinkedIn
Sign up for LUGOD event announcements
Your email address:
LUGOD Group on Facebook
'Like' LUGOD on Facebook:

Hosting provided by:
Sunset Systems
Sunset Systems offers preconfigured Linux systems, remote system administration and custom software development.

LUGOD: Linux Users' Group of Davis
PO Box 2082, Davis, CA 95617
Contact Us

LUGOD is a 501(c)7 non-profit organization
based in Davis, California
and serving the Sacramento area.
"Linux" is a trademark of Linus Torvalds.

Sponsored in part by:
Appahost Applications
For a significant contribution towards our projector, and a generous donation to allow us to continue meeting at the Davis Library.