Passing/Returning Strings to a C++ DLL

[wrxhokie]

I'm having trouble passing strings to a C++ DLL from my vb.net program. I get constant Read/Write memory error exceptions. My C++ code is as follows:

char * get_signal_desc(char * dev)
{
	bool status;
	char * desc;
	status = get_dev_signal_desc(dev, desc);
	return desc;
}

And i'm using this function in my vb.net code as follows:

Public Declare Function get_signal_desc Lib "Core_Wrapper.dll" (ByVal sig As String) As String

		Dim sig As String
		Dim desc As string
		desc.= Space(255)
		sig = "MRG31025"
		desc = get_signal_desc(sig)
		MessageBox.Show(desc.ToString)

I get the exception at the line where i call the C++ function. Can anyone help me figure out how to pass strings between a C++ DLL and vb.net program?