WinRT to Win32 string converstions

Question

Here are Sample code for converting WinRT String^ to char*

char* ToCharPtr(String^ str)
{
	int iSize = str->Length();
	std::wstring ws1( str->Data() );
	char* ascii = new char[iSize+1];
	ascii[iSize] = 0;
	for(int y= 0; y< iSize; y++)
	{
		ascii[y] = (char)ws1[y];
	}
	return ascii;
}

Here are Sample code for converting WinRT String Array ^  to char Array*

string* ToCharArrayPtr(const Array<String^>^ str)
{
	int i = 0;
	for each (String^ var in str)
	{
		i++;
	}
	if( i > 0)
	{
		string* sArray = new string[i];
		i = 0;
		for each (String^ var in str)
		{
			sArray[i++] = ToCharPtr(var);
		}
		return sArray;
	}
	else
		return NULL;
}

Here are Sample code for converting Win32 String to WinRt String^

String^ ToStringHat(char* ch)
{
	std::string s_str = std::string(ch);
	std::wstring wid_str = std::wstring(s_str.begin(), s_str.end());
	const wchar_t* w_char = wid_str.c_str();
	String^ p_string = ref new String(w_char);
	return p_string;
}

Answer 1

Using naked new statements like that is really bad coding practice. You should be using an exception-safe smart pointer such as std::unique_ptr instead. Also, for converting from Unicode to "ASCII" you should use either the wcstombs_s or the wcstombs_s_l function (see: http://msdn.microsoft.com/en-us/library/s7wzt4be.aspx ). The need for char* strings these days in Windows is almost non-existent. To the extent that you do need one it's likely that you need a utf-8 string to pass to the internet, in which case you should definitely be using wcstombs_s_l so that the string converts properly.

I strongly recommend reading this summary of modern C++ coding techniques and usages - http://msdn.microsoft.com/en-us/library/hh279654.aspx .

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Visual C++ MVP | Website | Blog | @mikebmcl | Windows Store DirectX Game Template

Answer 2

Hi Mike,

I agree with you, wcstombs_s or the wcstombs_s_l will work well.

Thanks for your suggestion.

Answer 3

FYI, I use

Platform::String^ UiUt::fromWstr(const std::wstring& ws)
{
   Platform::String^ plStr = ref new Platform::String(ws.c_str());
   return(plStr);
}

std::wstring UiUt::toWstr(Platform::String^ s)
{
   if (s == nullptr)
   {
      return(L"");
   }
   std::wstring ws(s->Data());
   return(ws);
}

Answer 4

Hi Bill,

SQLite uses UTF-8 strings so the conversion code you have won't work as expected when the system locale isn't en_* and/or when the connection string contains non-ASCII characters.

The following is what I'd do for the conversion:

std::string ConvertCxStringToUTF8(Platform::String^ stringToConvert)
{
	const wchar_t* data = stringToConvert->Data();

	auto requiredBufferSize = WideCharToMultiByte(
		CP_UTF8,
		WC_ERR_INVALID_CHARS,
		stringToConvert->Data(),
		static_cast<int>(stringToConvert->Length()),
		nullptr,
		0,
		nullptr,
		nullptr
		);

	if (requiredBufferSize == 0)
	{
		auto error = GetLastError();
		throw Platform::Exception::CreateException(HRESULT_FROM_WIN32(error));
	}

	requiredBufferSize++;

	std::string buffer(requiredBufferSize, 0);

	auto numBytesWritten = WideCharToMultiByte(
		CP_UTF8,
		WC_ERR_INVALID_CHARS,
		stringToConvert->Data(),
		static_cast<int>(stringToConvert->Length()),
		const_cast<char *>(buffer.data()),
		requiredBufferSize - 1,
		nullptr,
		nullptr
		);

	if (numBytesWritten != (requiredBufferSize - 1))
	{
		throw Platform::Exception::CreateException(E_UNEXPECTED, L"WideCharToMultiByte returned an unexpected number of bytes written.");
	}

	return buffer;
}

and then in the SqliteConnection::Open(void) member function, I'd have:

	auto str = ConvertCxStringToUTF8(ConnectionString);
	auto connStr = str.c_str();

	...

Though you could probably also just use:

	rc = sqlite3_open16(static_cast<const void *>(ConnectionString->Data()), &db);

The ConvertCxStringToUTF8 way is probably safer though since it bypasses any issues of endianness.

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Visual C++ MVP | Website | Blog | @mikebmcl | Windows Store DirectX Game Template