0001 template <typename T> void Vector<T>::expand() { //向量空间不足时扩容
0002    if ( _size < _capacity ) return; //尚未满员时，不必扩容
0003    T* oldElem = _elem; copyFrom( oldElem, 0, _capacity ); //容量加倍
0004    delete [] oldElem; //释放原空间
0005 }