Packing/unpacking binary data in C - doubles, 64 bits

[Kevin D. Clark]

Bruce Labitt writes:

> Kevin D. Clark wrote:
> > 2:  Typically, binary stuff is sent over the network in "network byte
> > order" and network byte order is big-endian.  This statement is not
> > universally agreed to -- in fact I used to work at a shop where they'd
> > never even considered this problem and it turned out that they were
> > sending (most) stuff over the wire in little-endian format.
> >
> >   
> That only works if both ends are the same - definitely not portable.  In 
> my case, the client is little-endian and the server is big-endian.

No, that always works and it is definitely portable.  Read what I said
again: when you transmit binary integers onto the wire, make sure they
exist in network-byte-order.

May I politely suggest that you consult a decent computer networking
book?  Please take a look at the functions htonl() and ntohl().



Question: from your various postings on this list, I gather that you
are using MPI.  If this is true, why aren't you just using things like
MPI_INT, MPI_DOUBLE, and possibly MPI_LONG_LONG?  Why not let your MPI
library take care of details like this for you?  I guarantee you that
any decent MPI implementation is going to be well-debugged and
efficient.  It should also take care of any endian issues that you
might encounter.

Regards,

--kevin
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