C#

//GetVersionEx exported from Kernel32.dll. 
// BOOL GetVersionEx(LPOSVERSIONINFO lpVersionInfo);

//The original structure passed to the function contains the following elements:
   //
   //typedef struct _OSVERSIONINFO
   //        { 
   //           DWORD dwOSVersionInfoSize; 
   //           DWORD dwMajorVersion; 
   //           DWORD dwMinorVersion; 
   //           DWORD dwBuildNumber; 
   //           DWORD dwPlatformId; 
   //           TCHAR szCSDVersion[ 128 ]; 
   //        } OSVERSIONINFO;
   //

using System;
   using System.Runtime.InteropServices;
   
   namespace OSInfo
   {
      class Class1
      {
         [ StructLayout( LayoutKind.Sequential )]
            public class OSVersionInfo 
         {
            public int dwOSVersionInfoSize;
            public int dwMajorVersion;
            public int dwMinorVersion;
            public int dwBuildNumber;
            public int dwPlatformId;
            [ MarshalAs( UnmanagedType.ByValTStr, 
               SizeConst=128 )]    
            public String szCSDVersion;
         }