1.2.1.4 Search in Container

• Distinguish among count, find, binary_search, lower_bound, upper_bound, and equal_range.

  

  1. For unsorted range, just generic find() or find_if() algorithm or count.
  2. For sorted range, Only four binary_search, lower_bound, upper_bound, and equal_range. are used on a sorted range.
  3. For set or map, It has own version, find(),count() and lower_bound, upper_bound, and equal_range
  4. Don’t use generic find() algorithm on a sorted range, use binary_search(). binary_search just return bool, not position.
  5. find() will return match iterator, if no match, it will return end()(for map or set). or last iterator(for generic algorithm). but Lower_bound will return a position anyway, match position or insert position(no match).
  6. Lower bound: first element that is greater-or-equal. Upper bound: first element that is strictly greater. equal_range return a pair of (lower_bound, Upper_bound).

     

  7. equal_range if two iterators equal, (no found,). if two iterators distance >=1, (find one or more match, can replace find() or count() function.) .
       std::sort (v.begin(), v.end()); 
       // 10 10 10 20 20 20 30 30 
      auto p =std::equal_range (v.begin(), v.end(), 20); 
      for ( auto i = p.first; i != p.second; ++i ) 
             std::cout << i->name << ’␣’; 
      
       //or code below: 
       if(distance(p.first, p.second)  >=1){ 
            cout<<"␣found␣match"<<endl; 
       }