× The internal search function is temporarily non-functional. The current search engine is no longer viable and we are researching alternatives.
As a stop gap measure, we are using Google's custom search engine service.
If you know of an easy to use, open source, search engine ... please contact support@midrange.com.



Value is the correct translation - in fact most C APIs require the parms passed by value.

Value causes the _content_ of the pointer to be passed. Const (or simply leaving the keyword off) causes the _address_ of the pointer to be passed. i.e. a pointer to the pointer. Not the same thing.

I don't think I've ever seen Options(*String) used with Const before - I'm actually a little surprised that it is valid.

Ignoring pointers for a moment and looking at it more generically. If you use Const then a pointer is passed - period. No matter what size the data is. So it results in 16 bytes being pushed onto the stack. If you use value then an item the size of the parm is pushed on the stack. Pass a 10i and 4 bytes get pushed. Pass 1,000 char and 1,000 bytes get pushed. As you can see very different.

Const can be made to work in this scenario. For example passing (say) a 100A field that includes the X'00' null terminator. That would result in a pointer to the surname being passed - and would work. But the proto is not strictly accurate and would not work generically for all situations.

So don't lie to the compiler - if you should be passing a pointer by value then do so.


Jon Paris

www.partner400.com
www.SystemiDeveloper.com

On Jul 10, 2017, at 6:17 AM, Danny Rodius <danny.rodius@xxxxxxxxx> wrote:

Hi,



Try to use the ifs function to open and read a directory.



Doc state the following:

DIR *opendir(const char *dirname)



However when we write the following PR it's not working



d openIFSDir Pr * ExtProc('opendir')

d * const options( *string )



Found the similar definition in Scott klements 'Working with the IFS in RPG'
chapter.7

Instead of using the const he uses the value. But isn't telling why.



When running now I get a correct opendir result.



Is there someone who know the reason for this difference between the doc and
the real world?



Best regards,

Danny

--
This is the RPG programming on the IBM i (AS/400 and iSeries) (RPG400-L) mailing list
To post a message email: RPG400-L@xxxxxxxxxxxx
To subscribe, unsubscribe, or change list options,
visit: http://lists.midrange.com/mailman/listinfo/rpg400-l
or email: RPG400-L-request@xxxxxxxxxxxx
Before posting, please take a moment to review the archives
at http://archive.midrange.com/rpg400-l.

Please contact support@xxxxxxxxxxxx for any subscription related questions.

Help support midrange.com by shopping at amazon.com with our affiliate link: http://amzn.to/2dEadiD


As an Amazon Associate we earn from qualifying purchases.

This thread ...

Follow-Ups:
Replies:

Follow On AppleNews
Return to Archive home page | Return to MIDRANGE.COM home page

This mailing list archive is Copyright 1997-2024 by midrange.com and David Gibbs as a compilation work. Use of the archive is restricted to research of a business or technical nature. Any other uses are prohibited. Full details are available on our policy page. If you have questions about this, please contact [javascript protected email address].

Operating expenses for this site are earned using the Amazon Associate program and Google Adsense.