Hi,
On Thu, 13 Mar 2008, Junio C Hamano wrote:
> Johannes Schindelin <Johannes.Schindelin@xxxxxx> writes:
>
> > diff --git a/builtin-merge-file.c b/builtin-merge-file.c
> > index adce6d4..cde4b2c 100644
> > --- a/builtin-merge-file.c
> > +++ b/builtin-merge-file.c
> > @@ -57,7 +57,8 @@ int cmd_merge_file(int argc, const char **argv, const char *prefix)
> >
> > if (!f)
> > ret = error("Could not open %s for writing", filename);
> > - else if (fwrite(result.ptr, result.size, 1, f) != 1)
> > + else if (result.size &&
> > + fwrite(result.ptr, result.size, 1, f) != 1)
> > ret = error("Could not write to %s", filename);
> > else if (fclose(f))
> > ret = error("Could not close %s", filename);
>
> Lol. We are dealing with N-byte quantity so we send one record of length
> N and make sure we processed one record, and it does not work when N is
> zero.
>
> We could instead send N records of size 1 and make sure we processed N
> records to lose the conditional instead, but the patch avoids unnecessary
> call to fread/fwrite so that is good. Thanks.
>
> It felt funny because my current bedtime reading happens to be "Zero: The
> Biography of a Dangerous Idea (ISBN 0140296476)".
Heh.
> > diff --git a/xdiff-interface.c b/xdiff-interface.c
> > index bba2364..61dc5c5 100644
> > --- a/xdiff-interface.c
> > +++ b/xdiff-interface.c
> > @@ -152,8 +152,8 @@ int read_mmfile(mmfile_t *ptr, const char *filename)
> > if ((f = fopen(filename, "rb")) == NULL)
> > return error("Could not open %s", filename);
> > sz = xsize_t(st.st_size);
> > - ptr->ptr = xmalloc(sz);
> > - if (fread(ptr->ptr, sz, 1, f) != 1)
> > + ptr->ptr = xmalloc(sz ? sz : 1);
> > + if (sz && fread(ptr->ptr, sz, 1, f) != 1)
> > return error("Could not read %s", filename);
> > fclose(f);
> > ptr->size = sz;
>
> Do you need to actually allocate ptr->ptr when sz is zero, instead of
> setting it to NULL, like:
>
> sz = xsize_t(st.st_size);
> ptr->size = sz;
> if (!sz)
> ptr->ptr = NULL;
> else {
> ptr->ptr = xmalloc(sz);
> if (fread(ptr->ptr, 1, sz, f) != sz)
> return error("Could not read %s", filename);
> }
> fclose(f);
I was going for the safe option. In theory, you are right, but I cannot
really be sure that e.g. a memcpy() with size 0 will not access the source
pointer at all.
Ciao,
Dscho
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