[DllImport("kernel32.dll",CharSet=CharSet.Unicode,SetLastError=true)]
public static extern IntPtr CreateFileW(string a,int b,int c,IntPtr d,int e,int f,IntPtr g);
[DllImport("kernel32.dll",CharSet=CharSet.Unicode,SetLastError=true)]
public static extern bool CloseHandle(IntPtr a);
[DllImport("kernel32.dll",CharSet=CharSet.Unicode,SetLastError=true)]
public static extern bool WriteFile(IntPtr a,IntPtr b,int c,IntPtr d,IntPtr e);
IntPtr p=Marshal.AllocCoTaskMem(512); 
IntPtr h=CreateFileW("C:\\111.txt",0x40000000,0,IntPtr.Zero,1,0,IntPtr.Zero);
bool z=WriteFile(h,p,200,IntPtr.Zero,IntPtr.Zero);    
Marshal.FreeCoTaskMem(p);    
bool b=CloseHandle(h);