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Groups > comp.lang.c > #5786

Re: pointer = &membuff[-2];

From Noob <root@127.0.0.1>
Newsgroups comp.lang.c
Subject Re: pointer = &membuff[-2];
Date 2011-06-10 13:03 +0200
Organization A noiseless patient Spider
Message-ID <isstm2$p9k$1@dont-email.me> (permalink)
References <isrcm7$q94$1@speranza.aioe.org> <ln8vtabj64.fsf@nuthaus.mib.org>

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Keith Thompson wrote:

> Converting the offset value from unsigned int to int is probably
> cleaner:
> 
>     int offset = n1 - n2;
>     sp = (struct dummy *) &membuff[offset];

Cleaner, perhaps, but it has implementation-defined behavior
when n1 < n2

"When [...] an unsigned integer is converted to its corresponding
signed integer, if the value cannot be represented the result is
implementation-defined."

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pointer = &membuff[-2]; "Bo S." <bo@boo.invalid> - 2011-06-09 21:07 +0000
  Re: pointer = &membuff[-2]; Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2011-06-09 16:47 -0600
    Re: pointer = &membuff[-2]; BGB <cr88192@hotmail.com> - 2011-06-09 22:59 -0700
    Re: pointer = &membuff[-2]; pete <pfiland@mindspring.com> - 2011-06-10 06:28 -0400
  Re: pointer = &membuff[-2]; Keith Thompson <kst-u@mib.org> - 2011-06-09 17:54 -0700
    Re: pointer = &membuff[-2]; Noob <root@127.0.0.1> - 2011-06-10 13:03 +0200
      Re: pointer = &membuff[-2]; Keith Thompson <kst-u@mib.org> - 2011-06-10 08:10 -0700
    Re: pointer = &membuff[-2]; Keith Thompson <kst-u@mib.org> - 2011-06-10 08:12 -0700
  Re: pointer = &membuff[-2]; Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-06-09 21:02 -0400
  Re: pointer = &membuff[-2]; James Kuyper <jameskuyper@verizon.net> - 2011-06-09 22:25 -0400
  Re: pointer = &membuff[-2]; Shao Miller <sha0.miller@gmail.com> - 2011-06-10 01:10 -0500
    Re: pointer = &membuff[-2]; Shao Miller <sha0.miller@gmail.com> - 2011-06-10 01:13 -0500
      Re: pointer = &membuff[-2]; Shao Miller <sha0.miller@gmail.com> - 2011-06-10 01:20 -0500
  Re: pointer = &membuff[-2]; Shao Miller <sha0.miller@gmail.com> - 2011-06-10 03:33 -0500
  Re: pointer = &membuff[-2]; James Kuyper <jameskuyper@verizon.net> - 2011-06-10 08:23 -0400
  Re: pointer = &membuff[-2]; Sherm Pendley <sherm.pendley@gmail.com> - 2011-06-10 09:30 -0400
  Re: pointer = &membuff[-2]; ImpalerCore <jadill33@gmail.com> - 2011-06-10 07:15 -0700

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