Re: To "const char *" and cast on free(), or "char *" and no cast...
- From
- Eric Wong <e@80x24.org>
- Date
- Oct 14, 2021, 23:36 UTC
- Message-ID
- <20211014233616.GA3348@dcvr>
- In-Reply-To
- <87mtnbfk0g.fsf@evledraar.gmail.com>
Ævar Arnfjörð Bjarmason <avarab@gmail.com> wrote:
> On Thu, Oct 14 2021, Phillip Wood wrote: > > [Changed $subject]
Thanks, I might not've noticed this if you hadn't.
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> > On 14/10/2021 01:10, Ævar Arnfjörð Bjarmason wrote: > >> The "checkout" command is one of the main sources of leaks in the test > >> suite, let's fix the common ones by not leaking from the "struct > >> branch_info". > >> Doing this is rather straightforward, albeit verbose, we need to > >> xstrdup() constant strings going into the struct, and free() the ones > >> we clobber as we go along. > > > > It's great to see these leaks being fixed. I wonder though if it would > > be better to change the structure definition so that 'name' and 'path' > > are no longer 'const'. That would be a better reflection of the new > > regime.[...] > > I think this is the right thing to do, but I'm not quite sure. There was > a thread at it here: > > https://lore.kernel.org/git/YUZG0D5ayEWd7MLP@carlos-mbp.lan/
I'd much prefer we keep const-ness for safety and documentation purposes.
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> Where I chimed in and suggested exactly what you're saying here, but the > consensus seemed to go the other way, and if you grep: > > git grep -F 'free((char *)' > > You can see that we use this pattern pretty widely.
I've been using unions to workaround APIs like free(3) for many years:
static inline void deconst_free(const void *ptr)
{
/* this initializer is a C99-ism */
union { const void *in; void *out; } deconst = { .in = ptr };free(deconst.out); }