Hirohito Higashi wrote:
> > > 2018-2-9(Fri) 20:30:22 UTC+9 Bram Moolenaar:
> > > > Patch 8.0.1481
> > > > Problem: Clearing a pointer takes two lines.
> > > > Solution: Add vim_clear() to free and clear the pointer.
> > > > Files: src/misc2.c, src/proto/misc2.pro, src/edit.c
> > > [...]
> > >
> > >
> > > In todo.txt
> > > > Use vim_clear() in more places, instead of vim_free() and assigning
> > > > NULL.
> > >
> > > I am working on the above items now.
> > > Wait about 6 hours.
> > >
> > > Remarks:
> > > It includes the following changes.
> > > - Since cast is dangerous and troublesome, I changed vim_clear() from
> > > function to macro.
> > >
> > > #define VIM_CLEAR(p) \
> > > do { \
> > > vim_free(p); \
> > > p = NULL; \
> > > } while (0)
> >
> > I want to avoid using a macro, because the argument may not be a simple
> > pointer.
>
> Hmm, at least my modified parts were all simple pointers.
As mentioned in the other message, it's logical that the pointer does
not have side effects.
> > Also, I intentionally only store NULL when it wasn't already set to NULL.
> > That should be faster.
>
> Ah, I fixed the patch to check that it's not NULL.
>
> > Why would the cast be dangerous?
>
> Casting can trick compiler type checks. The thing that the compiler
> does not tell even if you pass the wrong argument is "dangerous".
>
> For example, the following sample code will succeed in compiling. (on
> 64bit OS)
>
> --------8<--------
> #include <stdlib.h>
>
> void vim_clear(void **x)
> {
> if (*x != NULL) {
> free(*x);
> *x = NULL;
> }
> }
>
> int main(void)
> {
> long long a = 0;
>
> vim_clear((void **)a);
> return 0;
> }
> --------8<--------
OK, it's a stupid mistake, but it's possible.
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The Quest for the Holy Grail (Monty Python)
/// Bram Moolenaar -- [email protected] -- http://www.Moolenaar.net \\\
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