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Re: Array inside struct inside container

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none wrote:
> Victor Bazarov wrote:
>
>> A struct with an array as a data member is assignable.  The default
>> compiler-provided assignment operator performs memberwise
>> assignment that for array members means element-wise assignment.
>
>
> Thanks!  I was uninformed.  I've been using wrapper classes in my
> ignorance, which do perform a memcpy().  This means that I could
> get rid of them, but based on your example, I think the memcpy()
> might be slightly faster.  It's a micro-optimization, I know, but
> it looks like the compiler inserts something like a for-loop that
> invokes operator= for each element, where memcpy() is probably
> optimized down to basically a single REP-MOV instruction on x86.
> Or, maybe I'm just emotionally attached to my wrapper classes now
> and want to continue using them.

The compiler can easily optimize the memberwise copy into a memcpy() 
whenever that is possible (and deemed "slighly faster").

It is an old myth that memcpy() is always the fastest. Smart compilers 
can do a lot of things that is sometimes ever better (like taking 
advantage of known alignment and size).



Bo Persson

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Array inside struct inside container none <none@none.none> - 2011-08-16 19:12 +0000
  Re: Array inside struct inside container Victor Bazarov <v.bazarov@comcast.invalid> - 2011-08-16 15:28 -0400
    Re: Array inside struct inside container none <none@none.none> - 2011-08-16 20:07 +0000
      Re: Array inside struct inside container Leigh Johnston <leigh@i42.co.uk> - 2011-08-16 21:18 +0100
        Re: Array inside struct inside container James Kanze <james.kanze@gmail.com> - 2011-08-22 11:01 -0700
          Re: Array inside struct inside container Leigh Johnston <leigh@i42.co.uk> - 2011-08-22 20:44 +0100
            Re: Array inside struct inside container Leigh Johnston <leigh@i42.co.uk> - 2011-08-22 20:51 +0100
      Re: Array inside struct inside container Alain Ketterlin <alain@dpt-info.u-strasbg.fr> - 2011-08-16 23:26 +0200
      Re: Array inside struct inside container "Bo Persson" <bop@gmb.dk> - 2011-08-17 12:29 +0200
        Re: Array inside struct inside container Juha Nieminen <nospam@thanks.invalid> - 2011-08-17 13:06 +0000
  Re: Array inside struct inside container yatremblay@bel1lin202.(none) (Yannick Tremblay) - 2011-08-22 13:20 +0000
    Re: Array inside struct inside container Leigh Johnston <leigh@i42.co.uk> - 2011-08-22 14:42 +0100
      Re: Array inside struct inside container yatremblay@bel1lin202.(none) (Yannick Tremblay) - 2011-08-23 09:20 +0000

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