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Re: how does one access a specific address location in C?

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On 16/06/2016 19:34, Mark Storkamp wrote:
> In article <849b7311-65f7-4df2-8750-c94c2407823f@googlegroups.com>,
>  G G <gdotone@gmail.com> wrote:
>
>> there just has to be a way of looking at a memory location
>> given the location, doesn't it?
>
> Short answer: no.
>
> In the nascent days of home computers security wasn't much of an issue,
> and only one program typically ran at a time, so all of the available
> memory was given to the program that was running. Unless you're
> programming for an embedded controller, those days are pretty much over.
> Even the operating system doesn't have access to all memory. I'm not
> sure of the latest practice, but I remember when Intel introduced a
> supervisor mode that would get initialized by the BIOS and run above the
> OS. The supervisor has access to an area of memory that's hidden from
> the rest of the system.
>

Instead you have access to the virtual memory locations in your program. 
Although not all addresses may be set up to point to actual memory, so 
you need to know what's what.

On my Windows machine, I can access location 0x400000, but not 03ffffff.

But I can also allocate memory and make those raw locations known:

#define N 1024
int memory[N];

int main(void) {
     printf("Memory limits: %p to %p\n",&memory[0],&memory[N-1]);
}

This might show:

  Memory limits: 00405420 to 0040641C

(actually to 40641F inclusive)

and those actual addresses can be peeked and poked during the same 
invocation of the program.

-- 
Bartc

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how does one access a specific address location in C? G G <gdotone@gmail.com> - 2016-06-16 06:32 -0700
  Re: how does one access a specific address location in C? gazelle@shell.xmission.com (Kenny McCormack) - 2016-06-16 14:00 +0000
  Re: how does one access a specific address location in C? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-06-16 15:07 +0100
    Re: how does one access a specific address location in C? G G <gdotone@gmail.com> - 2016-06-16 07:18 -0700
      Re: how does one access a specific address location in C? Robert Wessel <robertwessel2@yahoo.com> - 2016-06-16 11:38 -0500
  Re: how does one access a specific address location in C? Mark Storkamp <mstorkamp@yahoo.com> - 2016-06-16 09:16 -0500
    Re: how does one access a specific address location in C? G G <gdotone@gmail.com> - 2016-06-16 07:50 -0700
      Re: how does one access a specific address location in C? G G <gdotone@gmail.com> - 2016-06-16 08:04 -0700
        Re: how does one access a specific address location in C? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-06-16 17:03 +0100
          Re: how does one access a specific address location in C? G G <gdotone@gmail.com> - 2016-06-16 10:01 -0700
            Re: how does one access a specific address location in C? Eric Sosman <esosman@comcast-dot-net.invalid> - 2016-06-16 14:29 -0400
            Re: how does one access a specific address location in C? Mark Storkamp <mstorkamp@yahoo.com> - 2016-06-16 13:34 -0500
              Re: how does one access a specific address location in C? BartC <bc@freeuk.com> - 2016-06-16 19:57 +0100
                Re: how does one access a specific address location in C? raltbos@xs4all.nl (Richard Bos) - 2016-06-18 20:50 +0000
                Re: how does one access a specific address location in C? Eric Sosman <esosman@comcast-dot-net.invalid> - 2016-06-18 17:23 -0400
                Re: how does one access a specific address location in C? raltbos@xs4all.nl (Richard Bos) - 2016-06-18 21:30 +0000
            Re: how does one access a specific address location in C? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-06-16 21:09 +0100
        Re: how does one access a specific address location in C? Mark Storkamp <mstorkamp@yahoo.com> - 2016-06-16 11:10 -0500
      Re: how does one access a specific address location in C? James Kuyper <jameskuyper@verizon.net> - 2016-06-16 13:41 -0400
        Re: how does one access a specific address location in C? G G <gdotone@gmail.com> - 2016-06-16 11:14 -0700
          Re: how does one access a specific address location in C? Keith Thompson <kst-u@mib.org> - 2016-06-16 11:26 -0700
          Re: how does one access a specific address location in C? James Kuyper <jameskuyper@verizon.net> - 2016-06-16 16:38 -0400
      Re: how does one access a specific address location in C? "James R. Kuyper" <jameskuyper@verizon.net> - 2016-06-18 11:32 -0400
  Re: how does one access a specific address location in C? James Kuyper <jameskuyper@verizon.net> - 2016-06-16 12:45 -0400
    Re: how does one access a specific address location in C? G G <gdotone@gmail.com> - 2016-06-16 10:19 -0700
    Re: how does one access a specific address location in C? Keith Thompson <kst-u@mib.org> - 2016-06-16 11:20 -0700
    Re: how does one access a specific address location in C? supercat@casperkitty.com - 2016-06-16 11:38 -0700
      Re: how does one access a specific address location in C? raltbos@xs4all.nl (Richard Bos) - 2016-06-18 13:19 +0000
        Re: how does one access a specific address location in C? supercat@casperkitty.com - 2016-06-18 07:11 -0700
          Re: how does one access a specific address location in C? Robert Wessel <robertwessel2@yahoo.com> - 2016-06-18 14:41 -0500
            Re: how does one access a specific address location in C? supercat@casperkitty.com - 2016-06-18 16:02 -0700
              Re: how does one access a specific address location in C? Les Cargill <lcargill99@comcast.com> - 2016-06-18 18:53 -0500
                Re: how does one access a specific address location in C? supercat@casperkitty.com - 2016-06-18 17:31 -0700
                Re: how does one access a specific address location in C? Les Cargill <lcargill99@comcast.com> - 2016-06-19 06:47 -0500
                Re: how does one access a specific address location in C? Robert Wessel <robertwessel2@yahoo.com> - 2016-06-19 00:37 -0500
                Re: how does one access a specific address location in C? BartC <bc@freeuk.com> - 2016-06-19 11:07 +0100
                Re: how does one access a specific address location in C? Robert Wessel <robertwessel2@yahoo.com> - 2016-06-19 16:21 -0500
              Re: how does one access a specific address location in C? Robert Wessel <robertwessel2@yahoo.com> - 2016-06-19 00:34 -0500

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