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From: Anton Shepelev <anton.txt@gmail.com>
Newsgroups: comp.lang.c
Subject: Re: Pointer conversion and alignment
Date: Sun, 18 Nov 2018 15:31:58 +0300
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Ben Bacarisse:

> If da_addemp returned the pointer one could write
>
>    memcpy(da_addemp(&a), &v, sizeof v);
>
> I'm not seeing the value of getting the pointer via
> another object.  Maybe it's because you want to provide
> the index (the current return value) as well?

Yes.  Also, in production code one shall check for error
before invoking memcpy().

> I'm the sort of programmer who'd be tempted to write
>
>    a[da_addamp(&a, ...)] = 42;
>
> which is not safe!

Well are you bold!  I try not to mix expressions with side
effects.

> > But the compiler -- why did it not optimise away my
> > accesses to int* objects through char** pointers even
> > with -O5?
>
> Sorry, I'm not sure what that's about.  Did you post an
> example?  If so, I must have missed it.  (Did you mean
> -Ofast rather than -O5?)

-O5 in GCC.  I didn't know it accepted any non-negative
integer with the -O option.  I have changed it to -O3 now.
My code:

   dynarray.h: https://pastebin.com/raw/VYFG3gBS
   dynarray.c: https://pastebin.com/raw/DQCEWgrH
   da_test.c : https://pastebin.com/raw/vMmq8NKJ

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