C# projects using both X86 and Any CPU

Question

Say I have 2 Winform projects A, B.

Project A (target .NET 2.0) has to be run on x86 (it is an external library) and for legacy reasons project B (target .NET 4.0) has

Answer 1

You may find the answer to your question in following blog post

http://blogs.microsoft.co.il/sasha/2012/04/04/what-anycpu-really-means-as-of-net-45-and-visual-studio-11/

Here is summary

.net 4.0

What AnyCPU used to mean up to .NET 4.0 (and Visual Studio 2010) is the following:

•If the process runs on a 32-bit Windows system, it runs as a 32-bit process. IL is compiled to x86 machine code.

•If the process runs on a 64-bit Windows system, it runs as a 64-bit process. IL is compiled to x64 machine code.

•If the process runs on an Itanium Windows system (has anyone got one? ;-) ), it runs as a 64-bit process. IL is compiled to Itanium machine code.

.net 4.5

In .NET 4.5 and Visual Studio 11 the cheese has been moved. The default for most .NET projects is again AnyCPU, but there is more than one meaning to AnyCPU now. There is an additional sub-type of AnyCPU, “Any CPU 32-bit preferred”, which is the new default (overall, there are now five options for the /platform C# compiler switch: x86, Itanium, x64, anycpu, and anycpu32bitpreferred). When using that flavor of AnyCPU, the semantics are the following:

•If the process runs on a 32-bit Windows system, it runs as a 32-bit process. IL is compiled to x86 machine code.

•If the process runs on a 64-bit Windows system, it runs as a 32-bit process. IL is compiled to x86 machine code.

•If the process runs on an ARM Windows system, it runs as a 32-bit process. IL is compiled to ARM machine code.

Answer 2

If any of your code calls 32-bit x86 libraries, the entire process needs to load as x86. No exceptions.

To do this, set the EXE project to x86, set DLL projects that have native x86 dependencies to x86, and for pure managed DLL projects you can use AnyCPU -- .NET will load them as x86 for your x86 EXE, but they can also load into x64 EXEs.

Remember that x86 code runs just fine on x64 processors running x64 Windows, with the help of the WOW64 compatibility layer.

(with limited exceptions: on Windows Server edition, WOW64 is an optional component, and in the preinstall environment there is no WOW64).