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| <== Date ==> | <== Thread ==> |
|---|
| Subject: | Re: mallocMustSucceed( 0 ) non-portable |
| From: | Till Straumann <[email protected]> |
| To: | Eric Norum <[email protected]> |
| Cc: | EPICS Tech-Talk <[email protected]>, Sheng Peng <[email protected]> |
| Date: | Mon, 30 Jan 2006 18:50:02 -0800 |
Should callocMustSucceed accept a 0 count, too?
e.g. replace
if(mem==0) {
with
if(mem==0 && size!=0 && count!= 0) {
Of course this means that callocMustSucceed and mallocMustSucceed can return a NULL pointer, which they currently never do.....
That's the dilemma. I thought about that but I believe requesting zero-sized memory and subsequent de-referencing the return value can be considered a programming error. Otherwise, I can't see how to avoid a memory leak.
On Jan 30, 2006, at 5:58 PM, Till Straumann wrote:
Sheng Peng recently discovered that
callocMustSucceed(0, x)
(a request for zero amount of memory) succeeds on linux but fails on RTEMS.
(This is because according to the ISO C and IEEE 1003.1 standard (http://www.opengroup.org/onlinepubs/009695399/functions/malloc.html) the allocator may either return NULL [rtems] or a unique pointer that is acceptable to free() [linux] in the case of a zero 'size' argument)
IMO, the EPICS implementation needs to be fixed to give consistent behavior and the API should define whether it is legal to request zero memory (with the side-effect of callocMustSucceed() returning a bogus or NULL pointer which probably is against its purpose) or not (with the possible side-effect of breaking code).
My suggestion would be replacing the
if (mem==0)
tests by
if (mem==0 && size != 0)
thus legalizing mallocMustSucceed(0) on all platforms.
-- Till
--
Eric Norum <[email protected] <mailto:[email protected]>>
Advanced Photon Source
Argonne National Laboratory
(630) 252-4793