C++ function pointer; no matching function

Question

So I have a assignment ask me to use randomized quick sort, and I found problems using function pointers.

The sort function is in rqs.cpp:

template <typename Item_Type>
void rqs_with_range(std::vector<Item_Type> &vec, int p, int q,
                int (*cmp)(Item_Type, Item_Type));

Then in my cpp file, I have something like this:

class Table{
   constructor....
   vector< vector<string>* >* holder; // table 
   int compare_str(vector<string>* a, vector<string>* b) {
      return a->at(compare_column) < b->at(compare_column) ? -1 :a->at(compare_column) == b->at(compare_column) ? 0 : 1;
  }

   void rqs{
      rqs_with_range( (*holder) , 1, int(holder->size()-1), &Table::compare_str);
   }
}

The compiler says I have error in function rqs, no matching function. my compare function is member function of Table, would it be the cause of problem?

Member functions are not functions, and pointers-to-member-functions aren't function pointers. Search this site, as this has been asked a million times already. — Kerrek SB
– Kerrek SB, Commented Mar 3, 2012 at 18:07

Bo Persson · Accepted Answer · 2012-03-03 18:07:30Z

1

Yes, that is a problem.

You could either make it a free function or a static member. Otherwise you have a hidden this parameter that affects the function signature.

answered Mar 3, 2012 at 18:07

Bo Persson

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Comments

ipc · Accepted Answer · 2012-03-03 18:10:39Z

0

If you already are using templates, then please don't use a function pointer. Use a function object instead:

template <typename Item_Type, typename Compare>
void rqs_with_range(std::vector<Item_Type> &vec, int p, int q, Compare comp);

Then the next problem: Make compare_str not a non-static member function, i.e. a function outside the Table class. With the modified rqs_with_range you are also able to solve your problem with std::mem_fun or std::bind but this does not make sense.

answered Mar 3, 2012 at 18:10

ipc

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