2010/8/5 archie14

class Compare { public: Compare (int i) : _i(i){} //this does not compile, but what's the proper way to define // function object for the sort method in ptr_vector? bool operator<(const A& v1, const A& v2) { return (v1.i > v2.i) &&(_i != 1); } private: int _i; };

Try making your operator const: bool operator<(const A& v1, const A& v2) *const* Roman Perepelitsa.

On 8/4/2010 8:12 PM, archie14 wrote:

I can't figure out how to use "sort" method in ptr_vector with the function object. Operator< should be defined, but for various reasons I cant define it in the class A, and I have to do the comparison between the A values using some other values.

Example:

class A { public: int i; };

class Compare { public: Compare (int i) : _i(i){} //this does not compile, but what's the proper way to define // function object for the sort method in ptr_vector? bool operator<(const A& v1, const A& v2) { return (v1.i> v2.i)&&(_i != 1); } private: int _i; };

ptr_vector<A> lst; Compare cmp(3); lst.sort(cmp);

The following works for me: #include <iostream> #include <functional> #include struct A { A(int i) : _i(i) { } int _i; }; struct Compare : std::binary_function { Compare(int i) : _i(i) { } bool operator()(const A& v1, const A& v2) const { return (v1._i < v2._i) && (_i != 1); } int _i; }; int main() { boost::ptr_vector<A> lst; lst.push_back(new A(3)); lst.push_back(new A(2)); lst.push_back(new A(1)); Compare cmp(3); lst.sort(cmp); boost::ptr_vector<A>::iterator a = lst.begin(); while (a != lst.end()) { std::cout << a++->_i << std::endl; } }