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Re: pass by address

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Barry Schwarz <schwarzb@dqel.com> writes:
> On Sun, 4 May 2014 00:08:07 -0400, "Bill Cunningham"
> <nospam@nspam.invalid> wrote:
>>    It wasn't the compiler it was the indent program. It mentioned = &. I 
>>can't seem to remember how to redirect stderr now. And this code works. So I 
>>don't know why people are telling me it doesn't. I think some people are 
>>just playing around with me and lying and trying to confuse me. Well here it 
>>is.
>>
>>#include <stdio.h>
>>
>>int main()
>>{
>>    int a = 15;
>>    int *p;
>>    p = &a;
>>    printf("%p\n", &p);
>
> Undefined behavior #1.
>
>>    printf("%p\n", p);
>
> Undefined behavior #2.
>
>>    printf("%d\n", *p);
>>}
>>
>>The result.
>>
>>0x7fff8a9bb7b0
>>0x7fff8a9bb7bc
>>15
>>
>>And everytime this is run there is a new addresss used.
>
> And this surprises you because?

Are you suggesting that the program's output varies because of the
undefined behavior?  That's theoretically possible, but very unlikely.

"%p" requires an argument of type void*, the above calls should be
written as:

    printf("%p\n", (void*)&p);
    printf("%p\n", (void*)p);

But omitting the cast is unlikely to have any *visible* effect on
almost all existing implementations.

If the output varies from one run to the next, it's just because memory
is allocated differently, perhaps by accident or perhaps because of a
deliberate security measure.

http://en.wikipedia.org/wiki/Address_space_layout_randomization

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Working, but not speaking, for JetHead Development, Inc.
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"

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pass by address "Bill Cunningham" <nosapm@nspam.invalid> - 2014-05-02 16:53 -0400
  Re: pass by address "Bill Cunningham" <nosapm@nspam.invalid> - 2014-05-02 17:03 -0400
    Re: pass by address "Bill Cunningham" <nosapm@nspam.invalid> - 2014-05-02 17:20 -0400
  Re: pass by address Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2014-05-02 17:58 -0400
    Re: pass by address "Bill Cunningham" <nosapm@nspam.invalid> - 2014-05-02 18:09 -0400
      Re: pass by address Barry Schwarz <schwarzb@dqel.com> - 2014-05-02 16:37 -0700
        Re: pass by address gazelle@shell.xmission.com (Kenny McCormack) - 2014-05-02 23:43 +0000
          Re: pass by address Richard <rgrdev_@gmail.com> - 2014-05-03 15:58 +0200
            Re: pass by address gazelle@shell.xmission.com (Kenny McCormack) - 2014-05-03 14:08 +0000
              Re: pass by address Barry Schwarz <schwarzb@dqel.com> - 2014-05-03 10:38 -0700
                Re: pass by address Richard <rgrdev_@gmail.com> - 2014-05-03 21:13 +0200
        Re: pass by address "Bill Cunningham" <nosapm@nspam.invalid> - 2014-05-03 01:46 -0400
        Re: pass by address "Bill Cunningaham" <nospam@nspam.invalid> - 2014-05-03 11:22 -0400
          Re: pass by address James Kuyper <jameskuyper@verizon.net> - 2014-05-03 12:13 -0400
          Re: pass by address Keith Thompson <kst-u@mib.org> - 2014-05-03 12:34 -0700
            Re: pass by address Richard <rgrdev_@gmail.com> - 2014-05-03 22:33 +0200
            Re: pass by address glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-05-03 21:21 +0000
              Re: pass by address "Bill Cunningham" <nospam@nspam.invalid> - 2014-05-04 00:08 -0400
                Re: pass by address Barry Schwarz <schwarzb@dqel.com> - 2014-05-03 21:52 -0700
                Re: pass by address Tonton Th <tth@nowhere.invalid> - 2014-05-04 08:44 +0000
                Re: pass by address Keith Thompson <kst-u@mib.org> - 2014-05-04 01:51 -0700
                Re: pass by address "Bill Cunningham" <nospam@nspam.invalid> - 2014-05-04 15:06 -0400
                Re: pass by address Barry Schwarz <schwarzb@dqel.com> - 2014-05-04 15:35 -0700
                Re: pass by address Richard <rgrdev_@gmail.com> - 2014-05-05 12:01 +0200
                Re: pass by address Barry Schwarz <schwarzb@dqel.com> - 2014-05-05 11:46 -0700
                Re: pass by address "Bill Cunningham" <nospam@nspam.invalid> - 2014-05-05 14:18 -0400
                Re: pass by address Barry Schwarz <schwarzb@dqel.com> - 2014-05-05 11:55 -0700
                Re: pass by address "Bill Cunningham" <nospam@nspam.invalid> - 2014-05-05 15:20 -0400
                Re: pass by address "Bill Cunningham" <nospam@nspam.invalid> - 2014-05-05 15:23 -0400
                Re: pass by address Ken Brody <kenbrody@spamcop.net> - 2014-05-06 11:02 -0400
                Re: pass by address "Bill Cunningham" <nospam@nspam.invalid> - 2014-05-06 14:46 -0400
                Re: pass by address Richard <rgrdev_@gmail.com> - 2014-05-05 12:00 +0200
                Re: pass by address Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-05-05 14:50 -0700
                Re: pass by address "Bill Cunningham" <nospam@nspam.invalid> - 2014-05-05 23:13 -0400
                Re: pass by address "Osmium" <r124c4u102@comcast.net> - 2014-05-05 23:09 -0500
                Re: pass by address "Bill Cunningham" <nospam@nspam.invalid> - 2014-05-06 08:55 -0400
                Re: pass by address Ken Brody <kenbrody@spamcop.net> - 2014-05-06 11:16 -0400
                Re: pass by address Richard <rgrdev_@gmail.com> - 2014-05-06 18:13 +0200
                Re: pass by address Kaz Kylheku <kaz@kylheku.com> - 2014-05-04 21:06 +0000
                Re: pass by address Kaz Kylheku <kaz@kylheku.com> - 2014-05-04 23:50 +0000
                Re: pass by address Keith Thompson <kst-u@mib.org> - 2014-05-04 12:36 -0700
                Re: pass by address "Bill Cunningham" <nospam@nspam.invalid> - 2014-05-05 14:21 -0400
                Re: pass by address Keith Thompson <kst-u@mib.org> - 2014-05-04 01:29 -0700
                Re: pass by address "Bill Cunningham" <nospam@nspam.invalid> - 2014-05-04 15:09 -0400
        Re: pass by address "Bill Cunningaham" <nospam@nspam.invalid> - 2014-05-03 11:32 -0400
  Re: pass by address Barry Schwarz <schwarzb@dqel.com> - 2014-05-02 16:43 -0700
    Re: pass by address "Bill Cunningham" <nosapm@nspam.invalid> - 2014-05-03 01:54 -0400
      Re: pass by address Richard <rgrdev_@gmail.com> - 2014-05-03 15:59 +0200
    Re: pass by address "Bill Cunningham" <nosapm@nspam.invalid> - 2014-05-03 02:08 -0400
      Re: pass by address "Bill Cunningaham" <nospam@nspam.invalid> - 2014-05-03 11:46 -0400
    Re: pass by address Kaz Kylheku <kaz@kylheku.com> - 2014-05-03 21:43 +0000

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