Function IsDigit

tests/gtest/gtest.h:2223–2225

  return isalnum(static_cast<unsigned char>(ch)) != 0;
}
inline bool IsDigit(char ch) {
  return isdigit(static_cast<unsigned char>(ch)) != 0;
}
inline bool IsLower(char ch) {
  return islower(static_cast<unsigned char>(ch)) != 0;
}