Sebastien Fortier wrote:

I would like to define two different sorting predicates for a class but I do not understand how to do this.

//meteorlogicalObj.hpp class meteorlogicalObj { public: meteorlogicalObj(int val, Point pt) : val_(val), pt_(pt){} virtual ~meteorlogicalObj() {}

// how would I go about creating these sorting functions that would work with the ptr_vector class bool sortOnValue(const meteorlogicalObj&, const meteorlogicalObj&); bool sortOnPoint(const meteorlogicalObj&, const meteorlogicalObj&); // ... private: int val_; Point pt_; };

//meteorlogicalObj.cpp #include "meteorlogicalObj.h"

bool meteorlogicalObj::sortOnValue(const meteorlogicalObj& metObj, const meteorlogicalObj& other) { return (metObj.val_ < other.val_); }

bool meteorlogicalObj::sortOnPoint(const meteorlogicalObj& metObj, const meteorlogicalObj& other) { return (metObj.pt_ < other.pt_); }

//main.cpp boost::ptr_vector<meteorlogicalObj> metObjVec;

//... fill vector

metObjVec.sort( sortOnValue() ); // this does not work, what is missing??? metObjVec.sort( sortOnPoint() ); // this does not work, what is missing???

I can see that I probably need the indect_fun but I do not know how to wrap my sorting function to pass them to the sorting function

You don't need to use indirect_fun<>, the algorithms do that themselves. What you is a functor that can be properly contructed: struct SortOnValue { typedef bool result_type; template< class M > bool operator()( const M& l, const M& r ) const { return l.value() < r.value(); } }; I assume that you have added a function called value to meteorlogicalObj. Alternatively you can make the class SortOnValue a friend to the class. -Thorsten