C++ count and map

Question

I am counting the number of times every word occurs in a text file. I would like to avoid cases and hence am doing tolower to my input and then counting. I have a map data struc

Answer 1

The third template parameter of std::map is a comparator type. You can provide your own comparison operation, in your case a case-insensitive one.

struct CaseInsensitive {
  bool operator()(std::string const& left, std::string const& right) const {
    size_t const size = std::min(left.size(), right.size());

    for (size_t i = 0; i != size; ++i) {
      char const lowerLeft = std::tolower(left[i]);
      char const lowerRight = std::tolower(right[i]);

      if (lowerLeft < lowerRight) { return true; }
      if (lowerLeft > lowerRight) { return false; }

      // if equal? continue!
    }

    // same prefix? then we compare the length
    return left.size() < right.size();
  }
};

Then instanciate your map:

typedef std::map MyWordCountingMap;

Note: only the first spelling is preserved (which seems okay with you)