How Can You Pass STL Strings as PCWSTR Parameters at the Windows API Boundaries?

We saw that a PCWSTR parameter is basically an input C-style null-terminated string pointer. If you have an STL string, how can you pass it when a PCWSTR is expected?

Well, it depends from the type of the STL string. If it’s a std::wstring, you can simply invoke its c_str method:

// DoSomethingApi(PCWSTR pszText, ... other stuff ...)

std::wstring someText = L"Connie";

// Invoke the wstring::c_str() method to pass the wstring
// as PCWSTR parameter to a Windows API:
DoSomethingApi(someText.c_str(), /* other parameters */);

The wstring::c_str method returns a pointer to a read-only C-style null-terminated “wide” (i.e. UTF-16 on Windows) string, which is exactly what a PCWSTR parameter expects.

If it’s a std::string, then you have to consider the encoding used by it. For example, if it’s a UTF-8-encoded string, you can first convert from UTF-8 to UTF-16, and then pass the UTF-16 equivalent std::wstring object to the Windows API invoking the c_str method as shown above.

If the std::string stores text encoded in a different way, you could still use the MultiByteToWideChar API to convert from that encoding to UTF-16, and pass the result std::wstring to the PCWSTR parameter invoking the wstring::c_str method, as well.