insert object into a set

Question

I want to insert a vector into a set like this:

set<vector<prmEdge> > cammini;
vector<prmEdge> vecEdge;
cammini.insert(vecEdge);

I have a compilation error like this:

prmPlanner.cpp:1285:   instantiated from here
/usr/include/c++/4.2/bits/stl_algobase.h:853: error: no match for ‘operator<’ in ‘__first1.__gnu_cxx::__normal_iterator<_Iterator, _Container>::operator* [with _Iterator = const prmEdge*, _Container = std::vector<prmEdge, std::allocator<prmEdge> >]() < __first2.__gnu_cxx::__normal_iterator<_Iterator, _Container>::operator* [with _Iterator = const prmEdge*, _Container = std::vector<prmEdge, std::allocator<prmEdge> >]()’
/usr/include/c++/4.2/bits/stl_algobase.h:855: error: no match for ‘operator<’ in ‘__first2.__gnu_cxx::__normal_iterator<_Iterator, _Container>::operator* [with _Iterator = const prmEdge*, _Container = std::vector<prmEdge, std::allocator<prmEdge> >]() < __first1.__gnu_cxx::__normal_iterator<_Iterator, _Container>::operator* [with _Iterator = const prmEdge*, _Container = std::vector<prmEdge, std::allocator<prmEdge> >]()’
make[1]: *** [prmPlanner.o] Errore 1

What should I do? Could somebody help me??

Thank you very much

Answer 1

It doesn't know how to compare vectors. You should supply operator< for vector<prmEdge> (or for prmEdge to automatically use std::lexicographical_compare for vectors) or use unordered_set if you don't actually need sorted set of vectors.

Answer 2

The object contained in the set must have operator < defined.

Answer 3

std::set needs its entries to be sortable. The std::vector is however not sortable.

Answer 4

std::set needs a predicate to sort elements. By default that's <, so you would need to define operator < for vector<prmEdge>. You can supply a custom predicate to std::set as well, see here.

Answer 5

agree with previous answers, just want to add that you can create global bool operator<(vector<T> v)

Answer 6

Since the elements in your set are vectors, which don't define operator<, you'll need to do one of two things: write a wrapper around vector that defines operator<, or else write a comparison functor, and supply it as a parameter when you create your set.