On Fri, 12 Nov 2010 16:04:39 +0100 Markus Armbruster <arm...@redhat.com> wrote:
> Luiz Capitulino <lcapitul...@redhat.com> writes: > > > On Fri, 12 Nov 2010 15:16:33 +0100 > > Markus Armbruster <arm...@redhat.com> wrote: > > > >> Luiz Capitulino <lcapitul...@redhat.com> writes: > >> > >> > On Fri, 12 Nov 2010 11:21:57 +0100 > >> > Markus Armbruster <arm...@redhat.com> wrote: > >> > > >> >> Luiz Capitulino <lcapitul...@redhat.com> writes: > >> [...] > >> >> > +QString *qemu_chr_mem_to_qs(CharDriverState *chr) > >> >> > +{ > >> >> > + MemoryDriver *d = chr->opaque; > >> >> > + > >> >> > + if (d->outbuf_size == 0) { > >> >> > + return qstring_new(); > >> >> > + } > >> >> > >> >> Why is this necessary? Is qstring_from_substr() broken for empty > >> >> substrings? If it is, it ought to be fixed! > >> > > >> > qstring_from_substr() takes a character range; outbuf_size stores a size, > >> > not a string length. So we do: > >> > > >> >> > + return qstring_from_substr((char *) d->outbuf, 0, d->outbuf_size > >> >> > - 1); > >> > > >> > If outbuf_size is 0, we'll be passing a negative value down. > >> > >> What's wrong with that? > > > > Although it's going to work with the current QString implementation, I don't > > think it's it's a good idea to rely on a negative index. > > How should I extract the substring of S beginning at index B with length > L? If I cant't do this for any B, L with interval [B,B+L-1] fully > within [0,length(S)], then the API is flawed, and ought to be replaced. Not sure we're talking about the same problem, anymore. When you said: > >> What's wrong with that? What did you mean? Did you mean 'let's not decrement outbuf_size' or did you mean 'let's pass -1 anyway'? Both seem wrong to me: the substring [0,-1] should be invalid and not decrementing outbuf_size is wrong, because it contains the buffer size and qstring_from_substr() will consume an additional char from the buffer (which should be '\0' today, but we shouldn't count on that). > > > Maybe, we could have: > > > > return qstring_from_substr((char *) d->outbuf, 0, > > d->outbuf_size > 0 ? d->outbuf_size - 1 : 0); > > > > A bit harder to read, but makes the function smaller. > > Err, doesn't qstring_from_substr(s, 0, 0) extract a substring of length > 1? Yeah, it's a bug. But that doesn't change my suggestion, can we do this way? This should fix the bug (not even compiled tested): diff --git a/qstring.c b/qstring.c index 4e2ba08..72a25de 100644 --- a/qstring.c +++ b/qstring.c @@ -42,10 +42,10 @@ QString *qstring_from_substr(const char *str, int start, int end) qstring = qemu_malloc(sizeof(*qstring)); - qstring->length = end - start + 1; - qstring->capacity = qstring->length; + qstring->length = end - start; + qstring->capacity = qstring->length + 1; - qstring->string = qemu_malloc(qstring->capacity + 1); + qstring->string = qemu_malloc(qstring->capacity); memcpy(qstring->string, str + start, qstring->length); qstring->string[qstring->length] = 0;