#define STATS_FRAME  0
#define STATS_DEVICE 1
#include <vector>
namespace {
void WideToMultiByte(LPCWSTR string, std::vector<char> *output) {
  const std::ctype<wchar_t> &CType = std::use_facet<std::ctype<wchar_t> >(std::locale());
  std::wstring wstr(string);
  output->clear();
  output->resize(wstr.length() + 1);
  CType._Narrow_s(wstr.data(), wstr.data() + wstr.length(), ' ', &(*output)[0], output->size());
}
void TW_CALL GetStatsCallback(void *value, void *clientData) {
  LPCWSTR wstr = L"";
  switch ((int)clientData) {
    case STATS_FRAME:
      wstr = DXUTGetFrameStats(DXUTIsVsyncEnabled());
      break;
    case STATS_DEVICE:
      wstr = DXUTGetDeviceStats();
      break;
  }
  std::vector<char> str;
  WideToMultiByte(wstr, &str);
  char **destPtr = (char **)value;
  TwCopyCDStringToLibrary(destPtr, &str[0]);
}
}

…

TwAddVarCB(bar, "Frame", TW_TYPE_CDSTRING, NULL, GetStatsCallback, (void *)STATS_FRAME, "Help='DX10 frame stats.'");
TwAddVarCB(bar, "Device", TW_TYPE_CDSTRING, NULL, GetStatsCallback, (void *)STATS_DEVICE, "Help='DX10 device stats.'");