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Re: pack() for producing C structs (Was: Re: How on earth did wemanage to break pack() so badly?)

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Peter Martini
May 1, 2013 17:29
Re: pack() for producing C structs (Was: Re: How on earth did wemanage to break pack() so badly?)
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On Wed, May 1, 2013 at 1:15 PM, Steffen Mueller <> wrote:
> On 05/01/2013 07:04 PM, Peter Martini wrote:
>> On Wed, May 1, 2013 at 12:53 PM, Steffen Mueller
>> <> wrote:
>>> [side-track]
>>> On 05/01/2013 06:44 PM, demerphq wrote:
>>>> My understanding of pack()s original intention was to allow one to
>>>> construct C structures in Perl. As such introduces a change which
>>>> basically means one cannot safely put a string into a C structure
>>>> without the possibility of the entire structure being corrupted by
>>>> doing so doesn't make sense.
>>> In all fairness, if you use pack to do that, you'll be writing VERY
>>> unportable code due to alignment, padding and friends. But don't listen
>>> to
>>> me: Have a look at the docs for Convert::Binary::C. Marcus knows a lot
>>> better than I do.
>> For what it's worth, I often use pack/unpack when I'm working with
>> network protocols.  The endianness and encoding are well defined and
>> may differ from the architecture of the system I'm working on.  The
>> main example I can think of was talking from a SPARC/Solaris or
>> Intel/linux host to a Windows service, which meant not only did it it
>> have to pay attention to endianness for the encoded length fields, it
>> had to convert encoded text data from UTF-16 to UTF-8 as well.
> That's entirely not the same as C structs. :)

Sorry, side-tracked the side-track :-)  I've done enough with C/C++
and various levels of optimization that I wouldn't ever try to pack a
C struct directly - but I've often used C structs as my documentation
for on on-disk / over-the-wire format, which is why I think of the two

> This being said, I'm surprised you haven't run into the "passing a scalar
> with UTF8bit set to pack("v/a")" issue. Are you running old perls?
> --Steffen

I haven't had to use that library for years, and yes it was an older
perl - maybe 5.8.4?  Certainly none of the clients using that were
5.10 or newer.

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