BSTR to std::string (std::wstring) and vice versa

BSTR to std::wstring:

// given BSTR bs
assert(bs != nullptr);
std::wstring ws(bs, SysStringLen(bs));

 
std::wstring to BSTR:

// given std::wstring ws
assert(!ws.empty());
BSTR bs = SysAllocStringLen(ws.data(), ws.size());

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Doc refs:

1. std::basic_string<typename CharT>::basic_string(const CharT*, size_type)
2. std::basic_string<>::empty() const
3. std::basic_string<>::data() const
4. std::basic_string<>::size() const
5. SysStringLen()
6. SysAllocStringLen()

You could also do this

#include <comdef.h>

BSTR bs = SysAllocString("Hello");
std::wstring myString = _bstr_t(bs, false); // will take over ownership, so no need to free

or std::string if you prefer

EDIT: if your original string contains multiple embedded \0 this approach will not work.

There is a c++ class called _bstr_t. It has useful methods and a collection of overloaded operators.

For example, you can easily assign from a const wchar_t * or a const char * just doing _bstr_t bstr = L"My string"; Then you can convert it back doing const wchar_t * s = bstr.operator const wchar_t *();. You can even convert it back to a regular char const char * c = bstr.operator char *(); You can then just use the const wchar_t * or the const char * to initialize a new std::wstring oe std::string.