make_heap() compilation issue

Question

compiling following:

class Compare
{
   bool cmp(const int& a, const int& b){return a>b;}
};

int main()
{
   vector<int, Compare> v;
   make_heap(v.begin(), v.end(), Compare());
}

result in compilation error - no class template named 'rebind' in 'class Compare'. What may be the reason? I use RedHat Linux with gcc. Thanks a lot.

Answer 1

You are missing parentheses near begin() and end() and are defining comparator the wrong way. This is what it should probably look like:

#include <vector>
#include <algorithm>
#include <functional>

struct Compare: std::binary_function<int const&, int const&, bool>
{
   public:
   bool operator()(const int& a, const int& b){return a>b;}
};

int main()
{
   std::vector<int> v;
   std::make_heap(v.begin(), v.end(), Compare());
   return 0;
}

Answer 2

std::vector<> doesn't have a comparator template argument; it has an allocator for its second argument.

You're using your comparator as an allocator in the vector template argument list.

class Compare
{
   public:
   bool operator()(const int& a, const int& b){return a>b;}
};

int main()
{
   vector<int> v;
   make_heap(v.begin(), v.end(), Compare());
}