Return string from c++ dll export function called from c#

Question

I am trying to return a string from a c++ dll export function. I am calling this function from c#. I have seen a lot of examples on the internet and I am really confused what to

Answer 1

On windows you can return string directly using BSTR (from wtypes.hincluded by windows.h). BSTRcan be created from standard wide string bySysAllocString function:

_declspec(dllexport) BSTR getDataFromTable(const char* tableName)
{
    return SysAllocString(L"String to return");
}

Then in C# you marshal the return type as BStr:

[DllImport("\\SD Card\\ISAPI1.dll", CallingConvention = CallingConvention.Cdecl )]
[return: MarshalAs(UnmanagedType.BStr)]
static extern string getDataFromTable(string tableName);