how to convert 'System::String ^' to 'BSTR'

[lencastro]

i am creating a addin for outlook express in vc++2005

I am trying to load xml to my code with the following code

STDMETHOD(GetCustomUI)(BSTR RibbonID, BSTR * RibbonXml)
{
Assembly^ assem=Assembly::GetExecutingAssembly();
Stream^ strm=
assem->GetManifestResourceStream("test.Xmlres.test.xml");
StreamReader^ reader= gcnew StreamReader(strm);
*RibbonXml= reader->ReadToEnd();
reader->Close();
strm->Close();
return S_OK;

}


but it showing an error in compile time:

error C2440: '=' : cannot convert from 'System::String ^' to 'BSTR'
No user-defined-conversion operator available, or
Cannot convert a managed type to an unmanaged type

 

[IceKettle]

I'm not very familiar with managed C++. I think you can first convert the
System::String to an wide char,an then convert this wide char to BSTR.
From MSDN you can get the first step as follows:

// convert_string_to_wchar.cpp
// compile with: /clr
#include < stdio.h >
#include < stdlib.h >
#include < vcclr.h >

using namespace System;

int main() {
String ^str = "Hello";

// Pin memory so GC can't move it while native function is called
pin_ptr<const wchar_t> wch = PtrToStringChars(str);
printf_s("%S\n", wch);

// Conversion to char* :
// Can just convert wchar_t* to char* using one of the
// conversion functions such as:
// WideCharToMultiByte()
// wcstombs_s()
// ... etc
size_t convertedChars = 0;
size_t sizeInBytes = ((str->Length + 1) * 2);
errno_t err = 0;
char *ch = (char *)malloc(sizeInBytes);

err = wcstombs_s(&convertedChars,
ch, sizeInBytes,
wch, sizeInBytes);
if (err != 0)
printf_s("wcstombs_s failed!\n");

printf_s("%s\n", ch);
}And in second step using ::SysAllocString to conver the wchar to BSTR or
using _bstr_t.