Hi John,
Your question is not a GCC question, it is a general programming question.
There are other forums that are more appropriate for your question. I don't
say this to chastise you, but rather to help you locate a better source of
information.
That being said...
So if I understand correctly, your communication protocol is passing "raw
structs" around.
In general, a struct is not platform agnostic. By platform I mean "OS + a
particular version of a particular compiler".
However, you can make a struct platform agnostic using this method (assuming
C-ish pseudocode):
---------------------------------------------------
typedef char byte;
struct MessageRecord
{
byte mID[4]; // big-endian int32
byte mAction[2]; // big-endian int16
byte mValue[8]; // big-endian int64
};
struct Message
{
int mID;
short mAction;
long mValue;
};
void OutputMessage(int fd, struct Message* msg)
{
struct MessageRecord rec;
HtonInt32(&rec.mID, msg->mID);
HtonInt16(&rec.mAction, msg->mAction);
HtonInt64(&rec.mValue, msg->mValue);
write(fd, &rec, sizeof rec);
}
void InputMessage(int fd, struct Message* msg)
{
struct MessageRecord rec;
read(fd, &rec, sizeof rec);
NtohInt32(&msg->mID, rec.mID);
NtohInt16(&msg->mAction, rec.mAction);
NtohInt64(&msg->mValue, rec.mValue);
}
---------------------------------------------------
That way the MessageRecord is platform agnostic and has a canonical "over
the wire format" (which also serves equally well as a canonical "on disk
file format"), regardless of source or destination, and does not suffer from
intra-member padding, end-of-structure alignment padding, and alignment
constraints.
Note: The Hton (host to network) and Ntoh (network to host) functions do
the correct endian packing for your platform and the used in the local
application Message. I leave those as an exercise.
HTH,
--Eljay
