.NET Software running on x64 but compiled on x86 for Any CPU (VS2008)

Question

I have a problem, whereby I’m getting runtime errors with a compiled program. This works fine in the development environment (x86), but not on the production environment (which is x64).

I found this article, which seems to imply that compiling the software as Any CPU may run the software as x64 software if it’s run in a 64 bit environment.

Is this the case, and if so, should software ever be compiled under Any CPU (as it seems to make for a mismatch between the two environments)?

It entirely depends on what you're doing. It's hard to give you advice without knowing what the environment is or what errors you're getting. — Jon Skeet, Feb 25 '11 at 14:03
The errors are inconsistent, and range from the program freezing to memory access errors. — Paul Michaels, Feb 25 '11 at 14:08
Windows on Windows for X64... not sure if that is used by .NET engine. — Tony The Lion, Feb 25 '11 at 14:52

score 2 · Accepted Answer · answered Feb 25 '11 at 15:06

AnyCPU is great if you are using managed code only. Managed code can be executed in a 32-bit-process or 64-bit-process. With AnyCPU, the framework chooses the bitness native to the OS.

The same is not true for unmanaged code. It needs to be compiled either as 32-bit or 64-bit code. Of course, due to the WoW64 subsystem, 64-bit Windows can run 64-bit processes.

But 64-bit processes cannot load 32-bit modules (DLLs, OCXs, etc.).

That means if your program is using unmanaged modules of some kind, better make sure to set the bitness manually so that all components have the same bitness.

.NET Software running on x64 but compiled on x86 for Any CPU (VS2008)

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