Re: How to pass a third argument to compare function?

From:

kasthurirangan.balaji@gmail.com

Newsgroups:

comp.lang.c++

Date:

Mon, 23 Jun 2008 07:21:15 -0700 (PDT)

Message-ID:

<115cca21-6746-43f7-b32f-3073fbfdff3d@x35g2000hsb.googlegroups.com>

On Jun 23, 7:08 pm, Lambda <stephenh...@gmail.com> wrote:

I defined a class:

class inverted_index
{
private:
std::map<std::string, std::vector<size_t> > index;
public:
std::vector<size_t> intersect(const std::vector<std::stri=

ng>&);

};

bool compare(const std::string&, const std::string&);

vector<size_t> inverted_index::intersect(const vector<string>& query)
{
        sort(query.begin(), query.end(), compare);
        vector<size_t> result = index[query.front()];

        return result;

}

bool compare(const string& s1, const string& s2)
{
        return index[s1].size() < index[s2].size();

}

In the intersect function, I want to sort the query by the
string matching vector size. So I define a compare function fort
'sort'.

I think I can't define compare as member function of inverted_index,
there is a current object as a implicit parameter for member
functions.
And the compare will have three parameters. I think it's wrong!

But if I define compare as a nonmember function with two parameters,
how can it access the index object. Make it 'friend' is useless here.

a compare functor could help you here. Pls find sample code below

Class Compare
{
  public:
    Compare(const int size)
      : size_(size) {} // this could be your required size or so

    bool operator()(const std::string &lhs, const std::string &rhs)
    {
      //your compare here
    }

  private:
    const int size_;
};

Thanks,
Balaji.