What's this error mean?

I'm trying to build some 3rd party code and I'm getting an error:

ValueToString.cpp:70: error: ‘std::basic_string::size_type’ is not a type

The offending code:

Code:

---

template <class T> static void ensureCapacity(std::basic_string<T>& buffer,
                                              std::basic_string<T>::size_type extraChars)
 {
  std::basic_string<T>::size_type requiredCapacity = buffer.length() + extraChars;
  if (requiredCapacity > buffer.capacity())
  {
    buffer.reserve(2 * requiredCapacity);
  }
 }

---

I don't see what the error is!

It means you need to add typename at the front of that phrase to indicate that std::basic_string<T>::size_type is referring to a type. Because it is based on T which could be anything, the compiler doesn't know whether size_type is a type or something else there. Adding typename resolves the ambiguity.

So is this the correct code? I added typename in two places:

Code:

---

template <class T> static void ensureCapacity(std::basic_string<T>& buffer,
                                              typename std::basic_string<T>::size_type extraChars)
 {
  typename std::basic_string<T>::size_type requiredCapacity = buffer.length() + extraChars;
  if (requiredCapacity > buffer.capacity())
  {
    buffer.reserve(2 * requiredCapacity);
  }
 }

---

I think so. Those are the only two places I notice.

Does it fix the error?