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Re: Different sizes of data and function pointers on a machine -- void* return type of malloc, calloc, and realloc

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On 6/25/2012 3:08 PM, Myth__Buster wrote:
> On Monday, June 25, 2012 9:16:07 AM UTC-7, christian.bau wrote:
>> On Jun 25, 5:08 pm, Myth__Buster <raghavani...@gmail.com> wrote:
>>
>>> Assume that the above code runs on a machine wherein the data pointers and function pointers are of different sizes. Then, what malloc returns is a function pointer but after casting it to void* while returning(Or, after assigning it to a void* variable internally and returning its value).
>>>
>>> Now, isn't malloc giving us the truncated address in the above context? Consider the same question applicable to calloc and realloc when used in such a context.
>>
>> malloc always returns a data pointer. You can ask it to return a data
>> pointer to some memory area that is big enough to hold a function
>> pointer, but it will still be a data pointer.
>>
>> Maybe the situation would be less confusing to you if you first
>> declare a struct with a single member that is a function pointer, then
>> use malloc to return a data pointer pointing to one such struct.
>
> Yeah, had thought of it earlier(struct-approach being feasible due to data pointer involvement). But, wanted to accomplish the same with a malloc call by passing the sizeof a function pointer. So, malloc's documentation should include a note on this, isn't it?

     Wouldn't that be sort of like "Warning: May Contain Nuts" on
a bag of peanuts?

     Aiming a function pointer at allocated memory (at any data object,
for that matter) is non-portable, as you've observed.  But filling the
allocated memory with something that can be called like a function is
also non-portable.  Seems to me that anyone playing such games already
needs a good deal of non-portable knowledge about the implementation:
He's purchased his packet of peanuts, on purpose.

-- 
Eric Sosman
esosman@ieee-dot-org.invalid

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Different sizes of data and function pointers on a machine -- void* return type of malloc, calloc, and realloc Myth__Buster <raghavanil4m@gmail.com> - 2012-06-25 09:08 -0700
  Re: Different sizes of data and function pointers on a machine -- void* return type of malloc, calloc, and realloc "christian.bau" <christian.bau@cbau.wanadoo.co.uk> - 2012-06-25 09:16 -0700
    Re: Different sizes of data and function pointers on a machine -- void* return type of malloc, calloc, and realloc Myth__Buster <raghavanil4m@gmail.com> - 2012-06-25 12:08 -0700
      Re: Different sizes of data and function pointers on a machine -- void* return type of malloc, calloc, and realloc James Kuyper <jameskuyper@verizon.net> - 2012-06-25 15:27 -0400
      Re: Different sizes of data and function pointers on a machine -- void* return type of malloc, calloc, and realloc Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-06-25 15:30 -0400
        Re: Different sizes of data and function pointers on a machine -- void* return type of malloc, calloc, and realloc Myth__Buster <raghavanil4m@gmail.com> - 2012-06-25 12:47 -0700
          Re: Different sizes of data and function pointers on a machine -- void* return type of malloc, calloc, and realloc Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-06-25 16:10 -0400
      Re: Different sizes of data and function pointers on a machine -- void* return type of malloc, calloc, and realloc Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-06-25 20:42 +0100
        Re: Different sizes of data and function pointers on a machine -- void* return type of malloc, calloc, and realloc Myth__Buster <raghavanil4m@gmail.com> - 2012-06-25 13:14 -0700
          Re: Different sizes of data and function pointers on a machine --   void* return type of malloc, calloc, and realloc Ian Collins <ian-news@hotmail.com> - 2012-06-26 08:30 +1200
            Re: Different sizes of data and function pointers on a machine -- void* return type of malloc, calloc, and realloc Myth__Buster <raghavanil4m@gmail.com> - 2012-06-25 13:53 -0700
              Re: Different sizes of data and function pointers on a machine --   void* return type of malloc, calloc, and realloc Ian Collins <ian-news@hotmail.com> - 2012-06-26 09:00 +1200
              Re: Different sizes of data and function pointers on a machine -- void* return type of malloc, calloc, and realloc James Kuyper <jameskuyper@verizon.net> - 2012-06-25 17:13 -0400
              Re: Different sizes of data and function pointers on a machine -- void* return type of malloc, calloc, and realloc Myth__Buster <raghavanil4m@gmail.com> - 2012-06-25 13:58 -0700
                Re: Different sizes of data and function pointers on a machine -- void* return type of malloc, calloc, and realloc Owen Jacobson <angrybaldguy@gmail.com> - 2012-06-26 00:03 -0400
          Re: Different sizes of data and function pointers on a machine -- void* return type of malloc, calloc, and realloc James Kuyper <jameskuyper@verizon.net> - 2012-06-25 16:47 -0400
          Re: Different sizes of data and function pointers on a machine -- void* return type of malloc, calloc, and realloc gordonb.vk4xa@burditt.org (Gordon Burditt) - 2012-06-25 16:06 -0500
          Re: Different sizes of data and function pointers on a machine -- void* return type of malloc, calloc, and realloc Keith Thompson <kst-u@mib.org> - 2012-06-25 14:17 -0700
          Re: Different sizes of data and function pointers on a machine -- void* return type of malloc, calloc, and realloc Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-06-25 17:24 -0400
  Re: Different sizes of data and function pointers on a machine -- void* return type of malloc, calloc, and realloc James Kuyper <jameskuyper@verizon.net> - 2012-06-25 12:52 -0400
    Re: Different sizes of data and function pointers on a machine -- void* return type of malloc, calloc, and realloc Myth__Buster <raghavanil4m@gmail.com> - 2012-06-25 12:28 -0700
      Re: Different sizes of data and function pointers on a machine -- void* return type of malloc, calloc, and realloc James Kuyper <jameskuyper@verizon.net> - 2012-06-25 15:59 -0400
      Re: Different sizes of data and function pointers on a machine -- void* return type of malloc, calloc, and realloc Keith Thompson <kst-u@mib.org> - 2012-06-25 14:08 -0700
      Re: Different sizes of data and function pointers on a machine -- void* return type of malloc, calloc, and realloc Nobody <nobody@nowhere.com> - 2012-06-26 21:29 +0100
  Re: Different sizes of data and function pointers on a machine -- void* return type of malloc, calloc, and realloc Keith Thompson <kst-u@mib.org> - 2012-06-25 13:13 -0700
  Re: Different sizes of data and function pointers on a machine -- void* return type of malloc, calloc, and realloc Paul N <gw7rib@aol.com> - 2012-06-25 13:17 -0700

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