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Re: best way to pass a multiple dimension variable to a method

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Lynn McGuire <lynnmcguire5@gmail.com> writes:

> On 12/21/2022 9:02 PM, Ben Bacarisse wrote:
>> Lynn McGuire <lynnmcguire5@gmail.com> writes:
>> 
>>> On 12/21/2022 2:37 PM, Lynn McGuire wrote:
>>>> What is the best way to pass a multiple dimension variable to a method in C++ ?
>>>> For instance, in C you could do the following:
>>>>       double xyz [5] [2] [14];
>>>>       ...
>>>>       amethod (xyz, ...);
>> Best is always going to depend on lost of as yet unspecified factors.
>> Are the sizes (other than the "top-level" one) always know at compile
>> time?  Are they always the same?
>> 
>>> I am looking at
>>>     https://www.educba.com/3d-arrays-in-c-plus-plus/
>> That hardly scratches the surface!
>> 
>>> and
>>>
>>> https://stackoverflow.com/questions/8767166/passing-a-2d-array-to-a-c-function
>> C has variably modified types which means you can pass run-time array
>> sizes to a C function.  C++ does not have this feature, but then that
>> page includes some C++ and does not use variably modified types (as far
>> as I could see).
>> You probably need to say more about your constraints to get better advice.
>
> I don't know if the array sizes are always known at compile time.  I
> suspect that they are but I am far from sure.
>
> I am moving a 750,000 line F77 / C calculation engine to C++ using a
> modified version of F2C.  F2C converts all multiple dimension arrays
> to single dimension arrays.  Sometimes I convert them back.  Still a
> few unknowns to work out.

You may better off just passing a pointer to the correct amount of space
and doing the indexing "by hand".

Do you ever need slices like column of row arrays?  That might be
another reason to do the index arithmetic yourself.

-- 
Ben.

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best way to pass a multiple dimension variable to a method Lynn McGuire <lynnmcguire5@gmail.com> - 2022-12-21 14:37 -0600
  Re: best way to pass a multiple dimension variable to a method Richard Damon <Richard@Damon-Family.org> - 2022-12-21 17:10 -0500
  Re: best way to pass a multiple dimension variable to a method Lynn McGuire <lynnmcguire5@gmail.com> - 2022-12-21 16:18 -0600
    Re: best way to pass a multiple dimension variable to a method Öö Tiib <ootiib@hot.ee> - 2022-12-21 18:03 -0800
      Re: best way to pass a multiple dimension variable to a method David Brown <david.brown@hesbynett.no> - 2022-12-22 15:03 +0100
    Re: best way to pass a multiple dimension variable to a method Ben Bacarisse <ben.usenet@bsb.me.uk> - 2022-12-22 03:02 +0000
      Re: best way to pass a multiple dimension variable to a method Lynn McGuire <lynnmcguire5@gmail.com> - 2022-12-22 02:01 -0600
        Re: best way to pass a multiple dimension variable to a method Öö Tiib <ootiib@hot.ee> - 2022-12-22 00:25 -0800
        Re: best way to pass a multiple dimension variable to a method Ben Bacarisse <ben.usenet@bsb.me.uk> - 2022-12-22 12:13 +0000
  Re: best way to pass a multiple dimension variable to a method Paavo Helde <eesnimi@osa.pri.ee> - 2022-12-22 09:07 +0200
  Re: best way to pass a multiple dimension variable to a method Lynn McGuire <lynnmcguire5@gmail.com> - 2022-12-22 22:10 -0600
  Re: best way to pass a multiple dimension variable to a method Lynn McGuire <lynnmcguire5@gmail.com> - 2022-12-22 22:23 -0600

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