pointer in unity

i am using unsafe in monoDevelop i compile my programme without probleme but i find the probleme in unity 3d :

using UnityEngine; using System.Collections; using System.Runtime.InteropServices; // DllImport

unsafe public class Myscript : MonoBehaviour {

 public string  ip;
 public string pas;
     public  void* VC;
 [DllImport("systemeAPI")]

 unsafe public  static extern   void* Opensysteme(  string  ip);
 // Use this for initialization
 void Start () {
      Opensysteme("10.0.1.12");

         
 }
 

}

Assets/Myscript.cs(5,21): error CS0227: Unsafe code requires the `unsafe' command line option to be specified

thk you