各位大侠，小的我正在用MFC写一个关于串口处理的DLL供C#调用，里面有一个属性m_COMPort保存串口信息。

CDLLTestApp theApp;



int n_COMPort = 0;



// CDLLTestApp initialization



BOOL CDLLTestApp::InitInstance()

{

	CWinApp::InitInstance();



	return TRUE;

}





extern "C" _declspec(dllexport) void SetCOMPort(int nCOMPort)

{

	n_COMPort = nCOMPort;

}



extern "C" _declspec(dllexport) int GetCOMPort()

{

	GetSelfModuleHandle();

	return n_COMPort;

}

在C#中有一个Helper类：

namespace AppMain

{

	public class DLLTestHelper

	{

		[DllImport("DllTest.dll", EntryPoint = "SetCOMPort")]

		public static extern void _SetCOMPort(int nCOMPort);



		[DllImport("DllTest.dll", EntryPoint = "GetCOMPort")]

		public static extern int _GetCOMPort();



		public void SetCOMPort(int nCOMPort)

		{

			_SetCOMPort(nCOMPort);

		}



		public int GetCOMPort()

		{

			return _GetCOMPort();

		}

	}

}

调用这个Helper的方法如下：

DLLTestHelper _Helper1 = new DLLTestHelper();

_Helper1.SetCOMPort(1);

DLLTestHelper _Helper2 = new DLLTestHelper();

_Helper1.SetCOMPort(2);



int n1 = _Helper1.GetCOMPort();



int n2 = _Helper2.GetCOMPort();

上面的代码是为了支持不同的串口，现在的问题是我执行_Helper1.SetCOMPort时_Helper2中的COMPort也同时变了。请问各位大侠DLL中应该怎样定义这个变量？这样在不同的实例SetCOMPort时不会影响到其它实例？