[AccessD] 32->64 bit conversion

[Jim Dettman]

Paul,

<< Should conditional compilation only be used in Access with some prescribed
caveats?>>

  There really are none, and you should not leave a project in an un-compiled state as it will run slower. 

   VBA has two major steps when working with code:

    1. When you enter a line of source, the text is tokenized and checked for basic syntax errors.  
    2. VBA "compiles" the tokenized code, which basically means it goes through a whole bunch of checks to figure out how all that code relates and if it's valid.   Last I knew, there were more than sixteen levels that the compiler would d code through before it was considered "compiled".    I'm putting compiled in quotes because un-like a lot of other languages where you end up with an .EXE, VBA doesn't do the same thing (it's not linked code).   Even with compiled code, it's still figuring out how to execute it at run time.    When you "compile" your VBA project, it's just cutting out some of those checks.

    You can have a VBA project with just source and no compiled code.   That's what /decompile leaves you with.   Any compiled code is marked as invalid and it will be removed when a compact and repair is done.

<<<< I understand Access likes to pre-compile its source and save it in the
database file (the front end in a FE-BE system).>>

 VBA doesn't do that on its own.   You must explicitly tell it to do that.   But VBA only executes compiled code, so if you don't do it before hand, it will compile at runtime.   It just won't save it.

 << If the source is written for conditional compilation (conditional according
to how Access was installed on the computer) how does Access know when
recompilation is required?>>

   I don't know for sure, but I would think it simply checks the values of any compiler constants against what the compiled code was compiled against.   If it spots a difference, then it compiles everything again, just as it would if you changed a line of code.

   With 32 vs 64 bit, that's what happens.   If you compile 32 bit, distribute as an .accdb, then run in 64 bit, VBA can (and does) compile on the fly.   But if you distribute as an .accde (which has no source), then it cannot and won't run.

HTH,
Jim.  
  

-----Original Message-----
From: AccessD On Behalf Of Paul Wolstenholme
Sent: Thursday, October 28, 2021 4:59 PM
To: Access Developers discussion and problem solving <accessd at databaseadvisors.com>
Subject: Re: [AccessD] 32->64 bit conversion

I have wondered about how conditional compilation works with Access.
I understand Access likes to pre-compile its source and save it in the
database file (the front end in a FE-BE system).
The database file can be distributed and even shared in a multi-user
environment.
So perhaps the computer that was used for compilation is not necessarily
the computer that executes the compiled code.
If the source is written for conditional compilation (conditional according
to how Access was installed on the computer) how does Access know when
recompilation is required?

One could avoid the issue by always decompiling the Access database before
another computer uses it and never sharing an Access database except as a
back end.
But Access wasn't designed with that limitation.

Should conditional compilation only be used in Access with some prescribed
caveats?

Paul Wolstenholme



> On Thu, Oct 28, 2021 at 11:59 AM Bill Benson <bensonforums at gmail.com>
> wrote:
> ...
> > When I was on a massive upscaling project, one with a lot of 32 bit API
> > functions pre-existing in the code, I would put wrappers around that luke
> >
> > #If VBA7 Then
> >      The declarations that are 64 bit
> >       Office Compatible
> > #Else
> >       The declarations that were 32 bit
> >       Office Compatible
> > #End If
> >
> >
> > Sometimes in addition or in substitution one would have also
> >
> > #If WIN64 Then…
> >
> > Etc.
> >
> > That is what conditional compilation is. Unfortunately this was only
> > sometimes all my code required. Often I had to change how many of the
> > variables in the rest of my code were declared as well. It is a long
> > learning curve (or was for me) and took a long time to properly upgrade
> > large apps to work in both environments. I think reading some of the
> links
> > others provided may be worth your time.
> >
>
>
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