string or stringbuilder between c++ and c#

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DLL

VisualC++

Hi,
I Created a C# Dll that use it in my C++ project. First i register and create a tlb file from that dll file, then i use it in my C++ project:

in my c++ project:

#import "..\..\dll\PMI_EPD.tlb" raw_interfaces_only

I pass a string to function of dll, as a parameter. but in dll it is empty!

in C# dll code:

public int GetText(string ss)
{
   return 5;
}

in c++ code:

InterfacePtr pmi(__uuidof(MY_Class));
int i;
pmi->GetText(L"2279947463", &i);

if i change string type in c#, StringBuilder, it will be correct. but when the function returns it crashes.

<pre>public int GetText(StringBuilder ss)
{
   return 5;
}</pre>

what do i do, please help me.