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Tommy · Posted: Tue Jul 01, 2003 3:41 am Post subject: VDS 5 extension exceptions

If any exception occurs in an extension DLL, VDS is supposed to return error 27:
Untrapped error in an external command or function.

VDS 5 doesn't return error 27 in such cases, unlike older VDS versions. Instead it
will return an error based on the extension's maxPar value, increased by 1.

The following slightly modified version of the DLL in extdoc10.zip clearly illustrates
the problem:
http://www.vdsworld.com/files/vds5extbug.zip

The only line that is added in it, is this one:

raise EConvertError.Create('Error 27 should be returned now, but instead maxPar + 1 is returned.');

jules · Posted: Tue Jul 01, 2003 8:33 am Post subject:

Thanks for posting this example, Tommy. I have tested it, and reported to Commercial Research what I think the problem is.

Incidentally, I was wrong when I stated in an earlier post that the maxpar value is no longer needed. It is. It is only the bufsize value that is ignored.

marty · Professional Member Joined: 10 May 2001 Posts: 789

I would like to personnaly thank Tommy for his research on this problem. Hope this will help resolve the VDS 5 problems that has been encountered with lots of extensions.

Hope Commercial Research will resolve this problem soon. Wink

FreezingFire · **Admin Team** Joined: 23 Jun 2002 Posts: 3508

Yes Tommy, thank you for finding what the exact problem is. Thumbs Up

Hortalonus · Posted: Tue Jul 01, 2003 3:23 pm Post subject:

Tommy rocks! Cool

vdsalchemist · Posted: Wed Jul 02, 2003 1:24 pm Post subject:

Alex · Newbie Joined: 29 Jan 2004 Posts: 2 Location: Germany

jules · Posted: Thu Jan 29, 2004 9:21 am Post subject:

Maxpar is only used by VDS so it can pad out every string passed to an extension with extra empty strings in order that an error does not occur when the params/arguments are read. In fact, maxpar is a global value for VDS so all extensions will receive strings padded to the largest value of maxpar specified by any of the extensions that have been loaded. (It just means the addition of extra null bytes on the end of the string.) The reason is to avoid the access violation that would occur if the extension called NextParam more times than the number of values that were actually supplied by the calling script.

Bufsize was required by earlier versions of VDS which reserved a block of memory to receive the string passed from the return value of a function back to VDS. VDS 5 has been improved so that you can pass any length of string or PChar it is reasonable to return as the return value of a function, therefore it is not necessary to specify a maximum size.

Alex · Newbie Joined: 29 Jan 2004 Posts: 2 Location: Germany

Many thanks for that very quick and great answer. Now I'm sure, that I use the parameterbuffer in the right way.