Function IsXDigit

rtpose_wrapper/src/gtest/gtest.h:2591–2593

  return isupper(static_cast<unsigned char>(ch)) != 0;
}
inline bool IsXDigit(char ch) {
  return isxdigit(static_cast<unsigned char>(ch)) != 0;
}

inline char ToLower(char ch) {
  return static_cast<char>(tolower(static_cast<unsigned char>(ch)));