C++ type signatures do not see optional parameters, thus, pretend that

your function does not have a default value:

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

struct A
{
   int double_it( int i, int j = 2 ) { return i * j; }
} a;

std::vector< int > v;

int main( )
{
   for ( std::vector< int >::iterator i = v.begin( ); i != v.end( ); ++ i )
   {
       a.double_it( * i );
   }

   // Write it as a for_each/bind
   std::for_each( v.begin(), v.end(), boost::bind( & A::double_it,

boost::ref( a ), _1, 2 ) );
}