Passing/Returning Strings to a C++ DLL

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:

Code:

---

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:

Code:

---

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?

Its solved. I found you have to use <MarshalAs(UnmanagedType.LPStr)> for all string types. And if your DLL returns a char *, then use stringbuilders.