C# preprocessor differentiate between operating systems

Question

Is it possible to differentiate between operating systems in C# using preprocessor? like :

#if OS_WINDOWS
//windows methods
#elif OS_MAC
//mac  methods
#elif OS_LINUX
//linux methods
#endif

Answer 1

What you are asking for is possible but needs a bit of work.

1. Define a preprocessor variable in your csproj

   <PropertyGroup Condition=" '$(OS)' == 'Windows_NT' ">
     <DefineConstants>_WINDOWS</DefineConstants>
   </PropertyGroup>
   

2. Use that in your code

   #if _WINDOWS
     // your windows stuff
   #else
     // your *nix stuff
   #endif
   

I find this technique useful when you have constants that are dependent on the OS (for example native library names)

Answer 2

No. Sadly you can't. And it is even logical: if you compile for AnyCPU, then your program is executable on any platform.

What you can do is create multiple project configurations, where you set the #define you want (in the Properties of the project, Build, Conditional compilation symbols).

But perhaps this is a XY problem... Normally you don't need to do it, and you can live with a

if (Environment.OSVersion.Platform == PlatformID.Win32NT)
{

}
else if (Environment.OSVersion.Platform == PlatformID.MacOSX)
{

}
else if (Environment.OSVersion.Platform == PlatformID.Unix)
{

}