Compiling 32-bit Apps for 64-bit Windows

32-bit applications have been around for a long time while 64-bit operating systems are only recently gaining popularity.  Therefore, I would expect that the 64-bit OS successors would make it easy to run legacy 32-bit apps.  And, they do as long as you compile them correctly.

I have been involved with the conversion of a motor drive configuration application from Visual J++ to C# .NET as described in this case study.  This application still relies on many legacy 32-bit drivers and DLLs.  When the converted application was installed Windows 7 x64 (64-bit), an error message similar to following message was issued:

"Error: Check to see if ActiveX control is Registered"

When the application is debugged, the following exception is being thrown and causing the crash:

"Class Not Registered (Exception of HRESULT: 0x80040154 (REGDB_E_CLASSNOTREG))"

Turns out that 32-bit drivers and DLLs are registered in a different area of Windows designated with "x86" (which stands for 32-bit) but my application was being run from the normal program area, which is a 64-bit area on x64 Windows.  To get Windows to run the application from zone x86, it must be complied as a 32-bit application.

In Visual Studio, among the project properties on the Build tab, there is the "Platform target" setting with three options: Any CPU, x86, and x64.  "Any CPU" sounds like the right choice because it is flexible- who doesn't want a CPU independent program.  This setting is fine if you install on a 32-bit OS.  But, my application is not flexible and only plays well when targeting an x86 platform.  The x64 setting would definitely be a mistake, declaring my program as pure 64-bit.

 I found out about this setting through Experts Exchange (here and here) and Xtreme .NET Talk.  Here's some official documentation from MSDN.  Once the change is made, installation and execution on the 64-bit platform is seamless.  Hope this helps.  May all your compilations be well targeted.

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