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I'm using Visual Studio 2010 to build a c# project that has both x86 and x64 targets. When I build using the IDE, I get the correct result of x64 and x86 targets.

When I use msbuild on the command line, I get everything built in x86, even though i specify x64 on the command line.

I didn't have this problem until I upgraded from .Net 4.0 to .Net 4.5.

With .Net 4.0 I was able to get my x64 targets even if I specified x86 on the command line.

I did a build in the .Net 4.0 environment and then another build in the .Net 4.5 environment and piped the output into log files. I noticed some differences in the log files but I think this is what is causing my issue:

In .Net 4.0 I see this line in the log file:

/reference:C:\Windows\Microsoft.Net\assembly\GAC_MSIL\Microsoft.CSharp\v4.0_4.0.0.0__b03f5f7f11d50a3a\Microsoft.CSharp.dll

In .Net 4.5 I see this line in the log file: /r:"C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework.NETFramework\v4.0\Microsoft.CSharp.dll"

Any ideas? It seams .Net 4.5 is using an x86 specific path.

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    What command line do you use to run msbuild? Do you build sln or csproj file? How do you pass specific configuration? Commented Apr 1, 2013 at 15:49
  • msbuild project.sln /p:Platform="x64" /t:Clean;Rebuild /p:Configuration=Debug Commented Apr 1, 2013 at 17:01
  • Is configuration correct in this line in the very beginning of log Building solution configuration "Debug|x64"? How do you understand that results incorrect? Which output directories are created - bin\x86\Debug or bin\x64\Debug? Commented Apr 1, 2013 at 17:33
  • Yes, Building solution configuration "Debug|x64". Every thing is put in bin\Debug. When I run the application I look in the task manager and see that it is an x86 process. I don't see that if I build it on my server that has .Net 4.0 or if I build it using the IDE. Commented Apr 1, 2013 at 18:09

1 Answer 1

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This could happen if your solution's x64 configuration is configured to build project as AnyCPU. A new configuration option in .Net 4.5, Prefer 32 bit, makes executables with Prefer32bit flag to start up as 32-bit processes on 64 bit machine. Since Prefer32bit flag is default in MSBuild targets, you will see the behavior you describe, i.e. upgrading from .Net 4.0 to .Net 4.5 will have your AnyCPU project to switch from 64 bit to 32 bit.

To make project (not solution) built for x64, specify it on command line:

msbuild project.csproj /p:Platform=x64

Notice, the command line is for .csproj, not for .sln.

Alternatively, verify you solution configuration in Configuration Manger and make sure it gets built as x64.

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2 Comments

Thanks! I was able to add /property:Prefer32bit=false to my msbuild command line and it looks like that solves the issue.
What switch to use with msbuild to build a solution to 64 bit?

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