1.5.1.5 Range

• Copy algorithm usage: 1) copy v2 to v1. 2) it use loop inside. Almost all uses of copy where the destination range is specified using an insert iterator should be replaced with calls to range member function.
  v1.clear(); 
  copy(v2.begin(), v2.end(), back_inserter(v1) ); 
   
  //prefer to use below three range memeber function 
  v1.insert(v1.end(), v2.begin(),v2.end() );  //better than copy 
  v1.assign(v2.begin(), v2.end() ) 
  // if want to replace all value in v1. 
  vector<int> v1( v2.begin(), v2.end() ); 
  // build from sractch. 
  v1.erase( v1.begin(), v1.begin()+5); 
  //erage range.
• A good example to explain why use range member function is below: When you use insert, inside of insert, STL will get distance(n elements) of v2,begin() and v2.end(). Then , It will reserve and move the all element in v1 just once according to the distance. If you use copy, it use loop insert one by one, It will move all element in v1 n times. if no space, it will reallocate and copy old element, just like common vector do. So use range member function, can save you a lot of time in this example.
  //don’t use front_inserter() here, 
  //because vector don’t support push_front() 
  copy(v2,begin() , v2.end(), 
            inserter(v, v.begin() ) ); 
   
  // a better method is here. 
  v1.insert(v1.begin(),  v2,begin() , v2.end());
• effective STL Item 5: Prefer range member functions to their single-element counterparts.
  1. Range construction:
  2. Range insertion:
  3. Range erasure:
  4. Range assignment:
  container::container(inputIterator1, inputIterator2); 
  container::insert(insertPosition, inputIt1, inputIt2); 
  container::erase(inputIterator1, inputIterator2); 
  container::assign(inputIterator1, inputIterator2);
• The main reason for using assign is to copy data from one type of container to another.
  1. For example, if you want to migrate the contents of an std::set<int> to an std::vector<int>, you can’t use the assignment operator, but you can use vector.assign(set.begin(), set.end()).
  2. Another example would be copying the contents of two containers holding different types that are convertible to one or the other; If you try to assign std::vector<Derived*> to an std::vector<Base*>, the assignment operator is insufficient.
  3. different part from one container to another.