HIPL

Struct nesting, flexible arrays

Asked by Christof Mroz

Is there a reason why the fields of struct hip_tlv_common are repeated for all parameter struct, rather than nesting struct hip_tlv_common as the first member? This would get rid of casts and code duplication.
See http://c-faq.com/struct/oop.jxh.html (edit: note that the cast given in the example can actually be avoided)

Also, why is pointer arithmetic preferred over using flexible arrays? Those would be more readable, less error-prone (well, than pointer arithmetic at least) and (in principle) be forward-compatible.
http://gcc.gnu.org/onlinedocs/gcc-4.1.2/gcc/Zero-Length.html (the part about [])

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Miika Komu
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Stefan Götz (stefan.goetz-deactivatedaccount) said : 		#1

Well, I'm not an author of the original code, but my guess is that there is actually no strong reason for this. On the other hand, I don't see the resources to actually change the status quo.

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Best Miika Komu (miika-iki) said : 		#2

Yes, struct hip_tlv_common could be reused better as long as it's a packed structure. Just a lot of places to change for this.

Flexible arrays is gcc specific, but I think we're not going for other compilers any time time soon. So why not.

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Christof Mroz (christof-mroz) said : 		#3

Thanks Miika Komu, that solved my question.

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Christof Mroz (christof-mroz) said : 		#4

On Wed, 30 Mar 2011 20:41:21 +0200, Miika Komu
<email address hidden> wrote:

> Miika Komu proposed the following answer:
> Yes, struct hip_tlv_common could be reused better as long as it's a
> packed structure.

Packedness ist not an issue with nested structs btw.

> Just a lot of places to change for this.

True. I didn't want to propose a change at all (the current code is not
broken), just curious.

> Flexible arrays is gcc specific, but I think we're not going for other
> compilers any time time soon. So why not.

They're in C99, IIRC.

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Diego Biurrun (diego-biurrun) said : 		#5

Please let's do this. I have had a look at the structs in lib/core/protodefs.h the other day and the amount of duplication is just staggering. Nesting structures would furthermore eliminate a very large part of the remaining casts in HIPL.