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Re: Do variables need to be initialized?

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On 04-Jun-15 12:17, David Kleinecke wrote:
> On Wednesday, June 3, 2015 at 9:42:03 AM UTC-7, gwowen wrote:
>> David Kleinecke wrote:
>>> It's all a matter of style.
>> 
>> True, but ... in post C90 versions, where you can mix code and
>> declarations, its often a good question to ask "if I don't know
>> what the initial value is, why am I declaring it here?"
>> ...
>
> Same points still apply. The C90 (and earlier) rule against mixing 
> declarations and statements was clearly wrong and I cannot imagine 
> why they imposed it. One reason it was silly is that mixing changes 
> nothing significant.

AIUI, early compilers worked line-by-line, and they needed all the
declarations in one place so they could set up the stack frame before
translating the following statements into code.  If a declaration came
later, then there would be no space left in the stack frame to put the
variable, and they couldn't go back and increase the frame size because
they'd already output the frame setup code--and the code in between that
assumed a particular frame size.

Once you can assume optimizing compilers that look at entire functions
(or at least blocks) before outputting anything, mixing declarations and
statements is an obvious improvement.

S

-- 
Stephen Sprunk         "God does not play dice."  --Albert Einstein
CCIE #3723         "God is an inveterate gambler, and He throws the
K5SSS        dice at every possible opportunity." --Stephen Hawking

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Thread

Do variables need to be initialized? fl <rxjwg98@gmail.com> - 2015-06-01 16:48 -0700
  Re: Do variables need to be initialized? Richard Heathfield <rjh@cpax.org.uk> - 2015-06-02 00:55 +0100
    Re: Do variables need to be initialized? Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2015-06-01 18:22 -0600
      Re: Do variables need to be initialized? Keith Thompson <kst-u@mib.org> - 2015-06-02 08:05 -0700
        Re: Do variables need to be initialized? Tim Rentsch <txr@alumni.caltech.edu> - 2015-07-11 08:07 -0700
          Re: Do variables need to be initialized? Keith Thompson <kst-u@mib.org> - 2015-07-11 16:47 -0700
            Re: Do variables need to be initialized? Tim Rentsch <txr@alumni.caltech.edu> - 2015-07-15 07:42 -0700
      Re: Do variables need to be initialized? Tim Rentsch <txr@alumni.caltech.edu> - 2015-07-11 08:03 -0700
  Re: Do variables need to be initialized? David Brown <david.brown@hesbynett.no> - 2015-06-02 09:15 +0200
    Re: Do variables need to be initialized? Tim Rentsch <txr@alumni.caltech.edu> - 2015-07-11 08:09 -0700
  Re: Do variables need to be initialized? David Kleinecke <dkleinecke@gmail.com> - 2015-06-03 09:30 -0700
    Re: Do variables need to be initialized? gwowen <gwowen@gmail.com> - 2015-06-03 09:41 -0700
      Re: Do variables need to be initialized? David Kleinecke <dkleinecke@gmail.com> - 2015-06-04 10:17 -0700
        Re: Do variables need to be initialized? Stephen Sprunk <stephen@sprunk.org> - 2015-06-05 11:10 -0500
          Re: Do variables need to be initialized? Bartc <bc@freeuk.com> - 2015-06-05 18:22 +0100
            Re: Do variables need to be initialized? Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2015-06-05 20:54 -0600
              Re: Do variables need to be initialized? Ian Collins <ian-news@hotmail.com> - 2015-06-06 15:49 +1200
                Re: Do variables need to be initialized? Dr Nick <nospam-4@temporary-address.org.uk> - 2015-06-06 08:42 +0100
                Re: Do variables need to be initialized? Keith Thompson <kst-u@mib.org> - 2015-06-06 13:11 -0700
                Re: Do variables need to be initialized? Dr Nick <nospam-4@temporary-address.org.uk> - 2015-06-07 16:58 +0100
                Re: Do variables need to be initialized? Bartc <bc@freeuk.com> - 2015-06-06 11:01 +0100
                Re: Do variables need to be initialized? Ian Collins <ian-news@hotmail.com> - 2015-06-07 09:07 +1200
                Re: Do variables need to be initialized? Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2015-06-06 15:06 -0600
                Re: Do variables need to be initialized? gwowen <gwowen@gmail.com> - 2015-06-08 05:39 -0700
                Re: Do variables need to be initialized? Bartc <bc@freeuk.com> - 2015-06-08 14:10 +0100
                Re: Do variables need to be initialized? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-06-08 14:21 +0100
                Re: Do variables need to be initialized? Bartc <bc@freeuk.com> - 2015-06-08 14:34 +0100
                Re: Do variables need to be initialized? David Brown <david.brown@hesbynett.no> - 2015-06-08 16:51 +0200
                Re: Do variables need to be initialized? Richard Heathfield <rjh@cpax.org.uk> - 2015-06-08 16:15 +0100
                Re: Do variables need to be initialized? Bartc <bc@freeuk.com> - 2015-06-08 17:31 +0100
                Re: Do variables need to be initialized? Ian Collins <ian-news@hotmail.com> - 2015-06-09 08:06 +1200
                Re: Do variables need to be initialized? Bartc <bc@freeuk.com> - 2015-06-08 22:58 +0100
                Re: Do variables need to be initialized? Keith Thompson <kst-u@mib.org> - 2015-06-08 08:27 -0700
                Re: Do variables need to be initialized? gwowen <gwowen@gmail.com> - 2015-06-08 08:01 -0700
            Re: Do variables need to be initialized? Stephen Sprunk <stephen@sprunk.org> - 2015-06-06 11:11 -0500
              Re: Do variables need to be initialized? Bartc <bc@freeuk.com> - 2015-06-06 19:09 +0100
                Re: Do variables need to be initialized? Robert Wessel <robertwessel2@yahoo.com> - 2015-06-06 13:57 -0500
                Re: Do variables need to be initialized? Keith Thompson <kst-u@mib.org> - 2015-06-06 13:52 -0700
                Re: Do variables need to be initialized? James Kuyper <jameskuyper@verizon.net> - 2015-06-06 20:57 -0400
                Re: Do variables need to be initialized? Stephen Sprunk <stephen@sprunk.org> - 2015-06-10 14:33 -0500
          Re: Do variables need to be initialized? Keith Thompson <kst-u@mib.org> - 2015-06-05 10:56 -0700

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