[Boost-users] Problem binding a predicate to random_shuffle()

21 Aug 2006

      Good day. 

After an initial post on the comp.lang.c++ usergroup, I was pointed to using
boost::bind for binding member functions as predicates for STL functions
(original example applied to sort()). The technique to use Boost's bind()
works well, except when used with STL's random_shuffle(). The following code
demonstrates a working call (on sort()) and a call that generates an error
(on random_shuffle()), both using the same technique.

The code:

#include <algorithm>
#include <functional>
#include <vector>
#include <boost/bind.hpp>

using namespace std;

class Foo {

   public:

      Foo() {

         for (int i=0; i < 5; i++) {
            dataVector.push_back(i*10);
            idVector.push_back(i);
         }
      }

      bool isLess(int leftID, int rightID) {
         return (dataVector[leftID] < dataVector[rightID]);
      }

      int customRand(int n) {
         return (rand() % n);
      }

      void mySort() {
         sort(idVector.begin(), idVector.end(), boost::bind(&Foo::isLess,
this, _1, _2));
      }

      void myShuffle() {
         random_shuffle(dataVector.begin(), dataVector.end(),
boost::bind(&Foo::customRand, this, _1));
      }

   private:
      vector<int> dataVector;
      vector<int> idVector;

};

int main(int argc, char** argv) {

   Foo myObj;

   myObj.myShuffle();
   myObj.mySort();

   return 0;

}

The error:

sort.cpp: In member function `void Foo::myShuffle()':
sort.cpp:33: error: no matching function for call to
`random_shuffle(__gnu_cxx::__normal_iterator<int*, std::vector<int,
std::allocator<int> > >, __gnu_cxx::__normal_iterator<int*,
std::vector<int, std::allocator<int> > >, boost::_bi::bind_t<int,
boost::_mfi::mf1<int, Foo, int>,
boost::_bi::list2<boost::_bi::value<Foo*>, boost::arg<1> > >)'
/usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/bits/stl_algo.h:1766:
note: candidates are: void std::random_shuffle(_RandomAccessIterator,
_RandomAccessIterator, _RandomNumberGenerator&) [with
_RandomAccessIterator = __gnu_cxx::__normal_iterator<int*,
std::vector<int, std::allocator<int> > >, _RandomNumberGenerator =
boost::_bi::bind_t<int, boost::_mfi::mf1<int, Foo, int>,
boost::_bi::list2<boost::_bi::value<Foo*>, boost::arg<1> > >]

The code compiles and runs fine using VC7.1 (Visual Studio 2003), but
gives an error using g++ (GCC) 3.4.4 (cygming special). Any help will
be greatly appreciated.

Kind regards,
Nelis Franken

PS: A follow-up post on the exact same problem to comp.lang.c++ directed me
to post it on the Boost list, since it was deemed off-topic. I hope someone
else on this list has had a similar STL problem with random_shuffle() and
boost::bind?