Hello, > what is the option of mcs.exe "-nostdlib"'s rule? And how to use it? I > run it as :"mcs -nostdlib sample.cs", why show the CS0518 error? Such > as "The predefined type `System.Object' is not defined" >From the man page: -nostdlib, -nostdlib+ Use this flag if you want to compile the core library. This makes the compiler load its internal types from the assembly being compiled. Miguel