How to use the correct unmanaged DLL file according CPU architecture? (32 / 64 bits)

Question

I have to use a C++ DLL file from an ASP.NET site. The site will be hosted on both 32 and 64 bits environments.

I have a 32 and 64 bits version of the unmanaged DLL

Answer 1

To get the compiler/framework to do most of the work you need to

1. have multiple build 'platforms' (typically x86, x64 - remove AnyCPU)
2. set each "platform target" configuration for each build config
3. we added conditional compilation symbols __WIN32 & __X64

List the different implementations for your functions according to platform, including different dll names if you need to have both installed at once.

#if __WIN32
        public delegate int Move(int target);
        [DllImport("my.dll", SetLastError = true, CharSet = CharSet.Auto)]
#elif __X64
        public delegate int Move(int target);
        [DllImport("my64.dll", SetLastError = true, CharSet = CharSet.Auto)]
#endif

Otherwise you can use loadlib and manage the marshalling yourself.