On Wed, Aug 14, 2002 at 06:59:44PM +0200, Yaniv Kaul wrote:
> What should I be using?
You left one out - "tvb_get_ntohl()".
That's the best one to use. If you use "tvb_get_ptr()" and then extract
a bunch of stuff by hand, that throws an exception unless the *entire*
structure on which you're doing the "tvb_get_ptr()" is available in the
frame, but if you get each individual field with, for example,
"tvb_get_ntohl()", the exception won't be thrown until you fetch a field
that's not available.
That means that if you have, for example, a short frame (captured with a
snapshot length less than the length of the frame), you will get more
stuff in the protocol tree.
Of the alternatives:
ntohl():
requires that <netinet/in.h> (on UNIX) or <winsock2.h>
(on Windows) be included, and Joerg Mayer is trying to
get rid of those
is passed a 32-bit integral value, but there's no
guarantee that a structure pointer set from
"tvb_get_ptr()" is properly aligned, so if you do
structp = tvb_get_ptr(tvb, offset, sizeof (struct));
foo = ntohl(structp->field);
you run the risk of getting an alignment fault on many
platforms (including the one I use at work, namely
SPARC/Solaris)
g_ntohl():
doesn't require that <netinet/in.h> (on UNIX) or
<winsock2.h> (on Windows) be included
is passed a 32-bit integral value, but there's no
guarantee that a structure pointer set from
"tvb_get_ptr()" is properly aligned, so if you do
structp = tvb_get_ptr(tvb, offset, sizeof (struct));
foo = ntohl(structp->field);
you run the risk of getting an alignment fault on many
platforms (including the one I use at work, namely
SPARC/Solaris)
pntohl()
doesn't require that <netinet/in.h> (on UNIX) or
<winsock2.h> (on Windows) be included
is passed a pointer, and dereferences it a byte at a
time, so it's not subject to alignment restrictions
so I'd vote for "pntohl()" unless you know *for certain* that the value
you're passing is aligned on the right boundary, in which case I'd vote
for "g_ntohl()".
