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Re: Struct casting

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On 12/ 6/11 11:00 AM, Tobias Blass wrote:
> On 2011-12-05, Edward Rutherford<edward.p.rutherford79@REMOVETHIS.gmail.com>  wrote:
>> This was pulled up at a code review. Code was similar to this:
>>
>> struct foo {
>>    int bar;
>>    int baz;
>> } f;
>>
>> int * i = (int *) f;
>>
>> The only way this could go wrong is if the struct contains padding before
>> its first member, but I don't think this would ever happen in practice
>> --- maybe on theoretical perverse implementations like the ones you guys
>> like to play with :)
>>
>> Who is right here by the letter of the law?
>>
> The standard guarantees that there is no padding before the first element, so
> this conversion is absolutely valid.

Not as written.  There's a * in the declaration f or an & in the 
initialisation of i missing.

> It may cause problems when another variable
> is placed before the 'bar',though, and I wouldn't bet that the person that adds
> the new member will change all these assignments.

As mentioned else-thread,

int *i = &f->bar;

would be better.

-- 
Ian Collins

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Thread

Struct casting Edward Rutherford <edward.p.rutherford79@REMOVETHIS.gmail.com> - 2011-12-05 21:52 +0000
  Re: Struct casting Harald van Dijk <truedfx@gmail.com> - 2011-12-05 13:58 -0800
  Re: Struct casting Tobias Blass <tobiasblass@gmx.net> - 2011-12-05 22:00 +0000
    Re: Struct casting Ian Collins <ian-news@hotmail.com> - 2011-12-06 11:10 +1300
  Re: Struct casting tom st denis <tom@iahu.ca> - 2011-12-05 14:06 -0800
    Re: Struct casting Ian Collins <ian-news@hotmail.com> - 2011-12-06 11:11 +1300
    Re: Struct casting James Kuyper <jameskuyper@verizon.net> - 2011-12-05 17:13 -0500
  Re: Struct casting Robert Wessel <robertwessel2@yahoo.com> - 2011-12-05 16:10 -0600
    Re: Struct casting Ian Collins <ian-news@hotmail.com> - 2011-12-06 11:13 +1300
    Re: Struct casting James Kuyper <jameskuyper@verizon.net> - 2011-12-05 17:15 -0500
  Re: Struct casting Keith Thompson <kst-u@mib.org> - 2011-12-05 14:16 -0800
    Re: Struct casting Lauri Alanko <la@iki.fi> - 2011-12-06 18:00 +0000
  Re: Struct casting blp@cs.stanford.edu (Ben Pfaff) - 2011-12-05 14:19 -0800
  Re: Struct casting jacob navia <jacob@spamsink.net> - 2011-12-06 08:29 +0100
    Re: Struct casting Malcolm McLean <malcolm.mclean5@btinternet.com> - 2011-12-06 00:15 -0800
      Re: Struct casting Ian Collins <ian-news@hotmail.com> - 2011-12-06 22:30 +1300
  Re: Struct casting jgk@panix.com (Joe keane) - 2011-12-08 21:08 +0000

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