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Re: best way to convert a Fortran implied do loop to C++

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On 1/7/2023 4:41 PM, Ben Bacarisse wrote:
> Ben Bacarisse <ben.usenet@bsb.me.uk> writes:
> 
>> Richard Damon <Richard@Damon-Family.org> writes:
>>
>>> On 1/7/23 7:55 AM, Ben Bacarisse wrote:
>>>> Lynn McGuire <lynnmcguire5@gmail.com> writes:
>>>>
>>>>> So what is the best way to convert a Fortran implied do loop to C++ ?
>>>>>
>>>>>         WRITE (2,2) (N (I), I = 1, 80)
>>>>>       2 FORMAT(' ',80A1)
>>>> Presumably the bounds are not always literals, and you probably also
>>>> want to general solution the works for multiple implied loops, some of
>>>> which might be nested?  So not much!
>>>> My first question would be how you translate WRITE/FORMAT combinations
>>>> with no loops as that's going to form the basis of a solution.
>>>> (I presume you know Fortran well enough to know that this is not the
>>>> same as putting a loop round the
>>>
>>> Althogh in C++ you COULD put the loop around the write equivalent
>>> since C++ doesn't automatically take the first character as carriage
>>> control and add the new line to the end (if you use the right
>>> functions).
>>
>> I would expect that with a clean translation the carriage control
>> handling (if wanted) would just come out in the wash.  Even in modern
>> Fortran (where the "carriage control" malarkey is obsolete) you can't
>> just turn an implied loop into an explicit one.  Presumably the
>> translating software already has some mechanism to iterate through the
>> format and that's what has to be driven by the implied loop.
>>
>> If, as I suppose is possible, the first character is still to be treated
>> specially, that should just work out correctly as the code iterates
>> through the format.
> 
> To add a bit more detail, I image that formats will be turned into
> run-time objects containing a 'compiled' version of the format
> mini-language.  A statement like
> 
>        WRITE(*, 2) A, X
>      2 FORMAT(I2, F5.2)
> 
> would turn into
> 
>    format_2.start();
>    format_2.write(UNIT_STAR, A);
>    format_2.write(UNIT_STAR, X);
>    format_2.end();
> 
> where the write method is a templated method that advances an internal
> pointer in the format "list" (it may, in fact, be a cyclic graph).  And
> 
>        WRITE(*,2) (N(I), X(I), I = 1, 6)
> 
> would turn into
> 
>    format_2.start();
>    for (int i = 1; i <= 6; i++) {
>        format_2.write(STAR, N[i]);
>        format_2.write(STAR, X[i]);
>    }
>    format_2.end();
> 
> The member function 'end' should be idempotent, because the write
> function will also call it when the last format specification is used.
> 
> I'm sure this is turn out to be way more complicated that it looks to me
> right now, but this feel like the gist of what's needed.

This is close to the way that F2C mimics the implied loop.

I have been using a std::string as an accumulator to maintain type safety.

Thanks,
Lynn

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best way to convert a Fortran implied do loop to C++ Lynn McGuire <lynnmcguire5@gmail.com> - 2023-01-06 23:00 -0600
  Re: best way to convert a Fortran implied do loop to C++ Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-01-07 12:55 +0000
    Re: best way to convert a Fortran implied do loop to C++ Richard Damon <Richard@Damon-Family.org> - 2023-01-07 11:07 -0500
      Re: best way to convert a Fortran implied do loop to C++ Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-01-07 21:48 +0000
        Re: best way to convert a Fortran implied do loop to C++ Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-01-07 22:41 +0000
          Re: best way to convert a Fortran implied do loop to C++ Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-01-07 22:46 +0000
          Re: best way to convert a Fortran implied do loop to C++ Lynn McGuire <lynnmcguire5@gmail.com> - 2023-01-07 21:29 -0600
  Re: best way to convert a Fortran implied do loop to C++ Lynn McGuire <lynnmcguire5@gmail.com> - 2023-01-11 14:16 -0600

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