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Re: C array descriptor

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On Wed, 25 Jun 2014 04:23:45 -0400, Andrew Haley  
<andrew29@littlepinkcloud.invalid> wrote:
> Roger Levy <roger.levy@gmail.com> wrote:

>> For the first time, I need to pass an array to an external function.
>> Does anyone know the data structure for C array descriptors?
>

Roger,

You want a pointer.  For most compilers, the pointer will point to
the address of the zero'th element of the array, i.e., the starting
address.

> C doesn't have array descriptors.  An array, when passed to a
> function, decays into a pointer to the first element.
>

Andrew,

C doesn't have arrays either.  C has pointers.  C has a subscript
operator [] which uses a pointer and scaled index.  What C has is
the ability to declare the space for an array.  That's it.  That's
the *only* thing in C that C has which involves an array.

int main(void)
{
    int abc[10]; /* array declaration */

    abc[2]=3; /* no array here */

#if 0
    [] is the subscript operator
    the subscript operator takes a non-void pointer and an index
    the subscript operator scales the index by the data size
    the subscript operator sums the pointer and scaled index
    abc is that pointer
    2 is the index
    3 is a value to store at the pointer+index*sizeof(int)
#endif

return(0);
}

As you can clearly see, the "array" is *NOT* passed to a function and
therefore shouldn't have "decayed into" a pointer to the first element.
Yet, the "array" in the code body *IS* a pointer to the first element.


Rod Pemberton
P.S.  Andrew, I really can't believe anyone let you maintain GCC.
Anton who is usually wrong about things knows more about how C
works and should work than you.

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Thread

C array descriptor Roger Levy <roger.levy@gmail.com> - 2014-06-24 19:45 -0700
  Re: C array descriptor Andrew Haley <andrew29@littlepinkcloud.invalid> - 2014-06-25 03:23 -0500
    Re: C array descriptor Segfaults R Us <seg4u@segue.org> - 2014-06-25 08:45 +0000
    Re: C array descriptor Roger Levy <roger.levy@gmail.com> - 2014-06-25 07:03 -0700
    Re: C array descriptor "Rod Pemberton" <dont_use_email@xnothavet.cqm> - 2014-06-25 18:13 -0400
      Re: C array descriptor Roger Levy <roger.levy@gmail.com> - 2014-06-25 17:03 -0700
      Re: C array descriptor Lars Brinkhoff <lars.spam@nocrew.org> - 2014-06-26 08:12 +0200
        Re: C array descriptor "Rod Pemberton" <dont_use_email@xnothavet.cqm> - 2014-06-26 18:07 -0400
          Re: C array descriptor Lars Brinkhoff <lars.spam@nocrew.org> - 2014-06-27 07:50 +0200
      Re: C array descriptor Andrew Haley <andrew29@littlepinkcloud.invalid> - 2014-06-26 04:10 -0500
        Re: C array descriptor "Rod Pemberton" <dont_use_email@xnothavet.cqm> - 2014-06-26 18:07 -0400
          Re: C array descriptor bruce.mcfarling@gmail.com - 2014-06-26 22:14 -0700
          Re: C array descriptor Andrew Haley <andrew29@littlepinkcloud.invalid> - 2014-06-27 03:39 -0500
            Re: C array descriptor Mark Wills <markwills1970@gmail.com> - 2014-06-27 03:32 -0700
              Re: C array descriptor Andrew Haley <andrew29@littlepinkcloud.invalid> - 2014-06-27 06:00 -0500
                Re: C array descriptor Roger Levy <roger.levy@gmail.com> - 2014-06-27 07:34 -0700
                Re: C array descriptor bruce.mcfarling@gmail.com - 2014-06-27 09:42 -0700
                Re: C array descriptor Roger Levy <roger.levy@gmail.com> - 2014-06-27 09:51 -0700
                Re: C array descriptor bruce.mcfarling@gmail.com - 2014-06-27 15:32 -0700
        Re: C array descriptor Bernd Paysan <bernd.paysan@gmx.de> - 2014-06-27 03:40 +0200

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