Question

My understanding is typedef acts as a synonym for a type, or can be used as an alias for a particular type. Also, the simplified codes below built perfectly. The question here is if I change the second line in the main function to :

Array<int>::ArrayIter<T> pa = a.begin(); // substituting back the typedef  “iterator” to its original form of ArrayIter<T>.

I get the following error message during compilation:

“ArrayIter” is not a member of “Array”

But the codes compiled perfectly using the “typedef” (iterator) notation. Why is “iterator” and ArrayIter suddenly not synonymous any more:

Reference codes below:

template<class T> class ArrayIter {
public:
ArrayIter(T* p) : m_p(p) {
}

private:
T* m_p;
};

template<class T> class Array {

public:
  Array(int size) throw (const char*) {
    if ( size > 0 ) {
       m_p = new T[size];
       m_size = size;
    } else {
   throw "Array: invalid array dimension";
}
  }

  // typedef and methods to support the new iterator for this class
  typedef ArrayIter<T> iterator;

  ArrayIter<T> begin() {
  return ArrayIter<T>(m_p);
  }

private:
  T* m_p;
  int m_size;
};


int main(int argc, char* argv[]) {

  Array<int> a(10);
  Array<int>::iterator pa = a.begin();

 return 0;
}

Answer 1

As the error says, ArrayIter is not a member of Array: it’s a separate class, declared in the surrounding namespace. Therefore, Array<int>::ArrayIter<T> is invalid, and should just be ArrayIter<int>.

iterator is a member of Array, so Array<int>::iterator is valid, and is an alias for ArrayIter<int>.