How to Convert Platform::String to Char*

How to convert Platform::String to char*?

Platform::String::Data() will return a wchar_t const* pointing to the contents of the string (similar to std::wstring::c_str()). Platform::String represents an immutable string, so there's no accessor to get a wchar_t*. You'll need to copy its contents, e.g. into a std::wstring, to make changes.

There's no direct way to get a char* or a char const* because Platform::String uses wide characters (all Metro style apps are Unicode apps). You can convert to multibyte using WideCharToMultiByte.

Convert Platform::String to std::string

Edit: see this answer for a better portable solution.

The problem is that std::string only holds 8-bit character data and your Platform::String^ holds Unicode data. Windows provides functions WideCharToMultiByte and MultiByteToWideChar to convert back and forth:

std::string make_string(const std::wstring& wstring)
{
  auto wideData = wstring.c_str();
  int bufferSize = WideCharToMultiByte(CP_UTF8, 0, wideData, -1, nullptr, 0, NULL, NULL);
  auto utf8 = std::make_unique<char[]>(bufferSize);
  if (0 == WideCharToMultiByte(CP_UTF8, 0, wideData, -1, utf8.get(), bufferSize, NULL, NULL))
    throw std::exception("Can't convert string to UTF8");

  return std::string(utf8.get());
}

std::wstring make_wstring(const std::string& string)
{
  auto utf8Data = string.c_str();
  int bufferSize = MultiByteToWideChar(CP_UTF8, 0, utf8Data, -1, nullptr, 0);
  auto wide = std::make_unique<wchar_t[]>(bufferSize);
  if (0 == MultiByteToWideChar(CP_UTF8, 0, utf8Data, -1, wide.get(), bufferSize))
    throw std::exception("Can't convert string to Unicode");

  return std::wstring(wide.get());
}

void Test()
{
  Platform::String^ str = L"विकास, વિકાસ, ਵਿਕਾਸ, Vikas";
  std::wstring wsstr(str->Data());
  auto utf8Str = make_string(wsstr); // UTF8-encoded text
  wsstr = make_wstring(utf8Str); // same as original text
}

How to convert from char to Platform::String^ (C++/CLI)

ref new Platform::String(&ch, 1);

C++/CX - I need to pass a Platform::String into a method that takes a const char*?

Disclaimer: I know little about C++/CX, and I'm basing the answer on the documentation here.

The String class contains 16-bit Unicode characters, so you can't directly get a pointer to 8-bit char-typed characters; you'll need to convert the contents.

If the string is known to only contain ASCII characters, then you can convert it directly:

String s = whatever();
std::string narrow(s.Begin(), s.End());
function_requiring_cstring(narrow.c_str());

Otherwise, the string will need translating, which gets rather hairy. The following might do the right thing, converting the wide characters to multi-byte sequences of narrow characters:

String s = whatever();
std::wstring wide(s.Begin(), s.End());
std::vector<char> buffer(s.Length()+1);  // We'll need at least that much
for (;;) {
    size_t length = std::wcstombs(buffer.data(), wide.c_str(), buffer.size());
    if (length == buffer.size()) {
        buffer.resize(buffer.size()*2);
    } else {
        buffer.resize(length+1);
        break;
    }
}
function_requiring_cstring(buffer.data());

Alternatively, you may find it easier to ignore Microsoft's ideas about how strings should be handled, and use std::string instead.

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