protocol header

hi @all,

I'm designing a new simple protocol and now I need a header for it.
There should only be 3 fields, one 32bit and 2 16bit fields -> 64bit
header (8byte). Due to the used library I need the data as a (unsigned
char*) for delivering. I thought about a struct to store the header but
I don't know how to cast it to the expected format for delivering.
Is there a way to store all this information and deliver it in a char[8]
which would be exactly 8byte long?

"Andreas Müller" wrote[color=blue]
> hi @all,
>
> I'm designing a new simple protocol and now I need a header for it.
> There should only be 3 fields, one 32bit and 2 16bit fields -> 64bit
> header (8byte). Due to the used library I need the data as a (unsigned
> char*) for delivering. I thought about a struct to store the header but
> I don't know how to cast it to the expected format for delivering.
> Is there a way to store all this information and deliver it in a char[8]
> which would be exactly 8byte long?[/color]

homework?
it's so simple. hint: typecast adress of struct to char*, or use
union and struct and...

> I'm designing a new simple protocol and now I need a header for it.[color=blue]
> There should only be 3 fields, one 32bit and 2 16bit fields -> 64bit
> header (8byte). Due to the used library I need the data as a (unsigned
> char*) for delivering. I thought about a struct to store the header but
> I don't know how to cast it to the expected format for delivering.
> Is there a way to store all this information and deliver it in a char[8]
> which would be exactly 8byte long?[/color]

Most compilers will place the struct you describe in 8 bytes, but some
compilers might not.
And on some processors the most significant byte will be first (Motorola)
and on others the least significant byte will be first (Intel). So you have
to take the byte order into account, f.ex by swapping the bytes on one of
the processor types.

Niels Dybdahl

Andreas Müller wrote:[color=blue]
> hi @all,
>
> I'm designing a new simple protocol and now I need a header for it.
> There should only be 3 fields, one 32bit and 2 16bit fields -> 64bit
> header (8byte). Due to the used library I need the data as a (unsigned
> char*) for delivering. I thought about a struct to store the header but
> I don't know how to cast it to the expected format for delivering.
> Is there a way to store all this information and deliver it in a char[8]
> which would be exactly 8byte long?[/color]

Hello,

if you are using C++, then reinterpret_cast might be a solution.

regards marbac

Andreas Müller wrote:
[color=blue]
> I'm designing a new simple protocol and now I need a header for it.
> There should only be 3 fields, one 32bit and 2 16bit fields -> 64bit
> header (8byte). Due to the used library I need the data as a (unsigned
> char*) for delivering. I thought about a struct to store the header but
> I don't know how to cast it to the expected format for delivering.
> Is there a way to store all this information and deliver it in a char[8]
> which would be exactly 8byte long?[/color]

Just use a char [8], or better, unsigned char [8] Put/get your data in it in
the format you want to use, and the code will work in all machines (in all
that use the same byte size, at least).

--
Salu2