[Guy Harris <guy@xxxxxxxxxxxx>]

On Feb 10, 2004, at 1:05 PM, Olivier Biot wrote:

> I am afraid that adding this to Ethereal today will require serious
> work and probably we'll need *ugh* global variables to implement this,

"This" meaning "make the Apply button active only if the filter is 
syntactically valid"?

BTW, note that the on-the-fly syntax checking we're now doing could 
cause problems if the expression you're constructing is, for example

	ip.addr == {hostname}

as it will, I assume, try compiling the current expression for each 
character you type or other change you make, and that involves doing a 
host-name-to-address lookup, and that could be *really* slow if a name 
server isn't responding.

> | You can tell whether a filter was empty by checking whether
> | "dfilter_compile()" supplied a non-null "dfilter_t" pointer - if the
> | pointer it supplied was null, the filter was empty.
>
> You'll want to add a method
> gboolean dfilter_equal(dfilter_t **dfp_a, dfilter_t **dfp_b)
> to epan/dfilter.[ch] which would compare the byte code of both
> compiled display filters and return true if both programs are
> identical.

Yes.  I think Ulf was questioning whether we'd want to do so *now*, as 
the intent is to produce the next release this week, I think.