I try to return a specific object of my std::map as follows :
const Vertex& Graph::getVertex(const std::pair<size_t, size_t>& pos) const // -> compile error
{
return this->_vertices[std::get<0>(pos)][std::get<1>(pos)];
}
Map :
std::map<size_t, std::vector<Vertex>> _vertices;
However, I get a compilation error if I let the constness of my getVertex function. Does it mean that accessing my map elements this way actually modify its instance ? Is there a better way to access my map elements ?
The error :
error: passing ‘const std::map<unsigned int, std::vector<Vertex> >’ as ‘this’ argument of ‘std::map<_Key, _Tp, _Compare, _Alloc>::mapped_type& std::map<_Key, _Tp, _Compare, _Alloc>::o\
perator[](const key_type&) [with _Key = unsigned int; _Tp = std::vector<Vertex>; _Compare = std::less<unsigned int>; _Alloc = std::allocator<std::pair<const unsigned int, std::vector<Vertex> > >; std::map\
<_Key, _Tp, _Compare, _Alloc>::mapped_type = std::vector<Vertex>; std::map<_Key, _Tp, _Compare, _Alloc>::key_type = unsigned int]’ discards qualifiers [-fpermissive]