Why does boost require &vector[0]? - c++

Question

Take edmonds_maximum_cardinality_matching for example. I can do:
vector<uint32_t> mate_map(n_vertices);
edmonds_maximum_cardinality_matching(g, &mate_map[0]);
But not:
vector<uint32_t> mate_map(n_vertices);
edmonds_maximum_cardinality_matching(g, mate_map);
Why is that so? A vector has all operations an array has right? NB: Here is the error message (for the second snippet) which I could not really handle:
In file included from main.C:5:0:
/usr/include/boost/graph/max_cardinality_matching.hpp: In instantiation of ‘static void boost::extra_greedy_matching<Graph, MateMap>::find_matching(const Graph&, MateMap) [with Graph = boost::adjacency_list<boost::setS, boost::vecS, boost::undirectedS>; MateMap = std::vector<unsigned int>]’:
/usr/include/boost/graph/max_cardinality_matching.hpp:842:63: required from ‘bool boost::matching(const Graph&, MateMap, VertexIndexMap) [with Graph = boost::adjacency_list<boost::setS, boost::vecS, boost::undirectedS>; MateMap = std::vector<unsigned int>; VertexIndexMap = boost::vec_adj_list_vertex_id_map<boost::no_property, long unsigned int>; AugmentingPathFinder = boost::edmonds_augmenting_path_finder; InitialMatchingFinder = boost::extra_greedy_matching; MatchingVerifier = boost::no_matching_verifier]’
/usr/include/boost/graph/max_cardinality_matching.hpp:885:19: required from ‘void boost::edmonds_maximum_cardinality_matching(const Graph&, MateMap, VertexIndexMap) [with Graph = boost::adjacency_list<boost::setS, boost::vecS, boost::undirectedS>; MateMap = std::vector<unsigned int>; VertexIndexMap = boost::vec_adj_list_vertex_id_map<boost::no_property, long unsigned int>]’
/usr/include/boost/graph/max_cardinality_matching.hpp:894:70: required from ‘void boost::edmonds_maximum_cardinality_matching(const Graph&, MateMap) [with Graph = boost::adjacency_list<boost::setS, boost::vecS, boost::undirectedS>; MateMap = std::vector<unsigned int>]’
main.C:20:51: required from here
/usr/include/boost/graph/max_cardinality_matching.hpp:617:58: error: no matching function for call to ‘put(std::vector<unsigned int>&, boost::iterators::detail::iterator_facade_base<boost::range_detail::integer_iterator<long unsigned int>, long unsigned int, boost::iterators::random_access_traversal_tag, long unsigned int, long int, false, false>::reference, boost::graph_traits<boost::adjacency_list<boost::setS, boost::vecS, boost::undirectedS> >::vertex_descriptor)’
put(mate, *vi, graph_traits<Graph>::null_vertex());
^
/usr/include/boost/graph/max_cardinality_matching.hpp:617:58: note: candidates are:
In file included from /usr/include/boost/graph/adjacency_list.hpp:36:0,
from main.C:4:
/usr/include/boost/property_map/property_map.hpp:124:15: note: template<class T, class V> void put(T*, std::ptrdiff_t, const V&)
inline void put(T* pa, std::ptrdiff_t k, const V& val) { pa[k] = val; }
^
/usr/include/boost/property_map/property_map.hpp:124:15: note: template argument deduction/substitution failed:
In file included from main.C:5:0:
/usr/include/boost/graph/max_cardinality_matching.hpp:617:58: note: mismatched types ‘T*’ and ‘std::vector<unsigned int>’
put(mate, *vi, graph_traits<Graph>::null_vertex());
^
In file included from /usr/include/boost/graph/adjacency_list.hpp:36:0,
from main.C:4:
/usr/include/boost/property_map/property_map.hpp:193:8: note: template<class K, class V> void boost::put(const boost::writable_property_map_archetype<K, V>&, const typename boost::writable_property_map_archetype<K, V>::key_type&, const typename boost::writable_property_map_archetype<K, V>::value_type&)
void put(const writable_property_map_archetype<K,V>&,
^
/usr/include/boost/property_map/property_map.hpp:193:8: note: template argument deduction/substitution failed:
In file included from main.C:5:0:
/usr/include/boost/graph/max_cardinality_matching.hpp:617:58: note: ‘std::vector<unsigned int>’ is not derived from ‘const boost::writable_property_map_archetype<K, V>’
put(mate, *vi, graph_traits<Graph>::null_vertex());
^
In file included from /usr/include/boost/graph/adjacency_list.hpp:36:0,
from main.C:4:
/usr/include/boost/property_map/property_map.hpp:307:3: note: template<class PropertyMap, class Reference, class K, class V> void boost::put(const boost::put_get_helper<Reference, PropertyMap>&, K, const V&)
put(const put_get_helper<Reference, PropertyMap>& pa, K k, const V& v)
^
/usr/include/boost/property_map/property_map.hpp:307:3: note: template argument deduction/substitution failed:
In file included from main.C:5:0:
/usr/include/boost/graph/max_cardinality_matching.hpp:617:58: note: ‘std::vector<unsigned int>’ is not derived from ‘const boost::put_get_helper<Reference, PropertyMap>’
put(mate, *vi, graph_traits<Graph>::null_vertex());
^
In file included from /usr/include/boost/graph/properties.hpp:21:0,
from /usr/include/boost/graph/adjacency_list.hpp:44,
from main.C:4:
/usr/include/boost/graph/property_maps/null_property_map.hpp:32:10: note: template<class K, class V> void boost::put(boost::null_property_map<K, V>&, const K&, const V&)
void put(null_property_map<K,V>& /*pm*/, const K& /*key*/, const V& /*value*/)
^
/usr/include/boost/graph/property_maps/null_property_map.hpp:32:10: note: template argument deduction/substitution failed:
In file included from main.C:5:0:
/usr/include/boost/graph/max_cardinality_matching.hpp:617:58: note: ‘std::vector<unsigned int>’ is not derived from ‘boost::null_property_map<K, V>’
put(mate, *vi, graph_traits<Graph>::null_vertex());
^
In file included from /usr/include/boost/graph/adjacency_list.hpp:246:0,
from main.C:4:
/usr/include/boost/graph/detail/adjacency_list.hpp:1760:5: note: template<class Config, class Base, class Property, class Key, class Value> void boost::put(Property, boost::adj_list_helper<Config, Base>&, const Key&, const Value&)
put(Property p, adj_list_helper<Config, Base>& g,
^
/usr/include/boost/graph/detail/adjacency_list.hpp:1760:5: note: template argument deduction/substitution failed:
In file included from main.C:5:0:
/usr/include/boost/graph/max_cardinality_matching.hpp:617:58: note: mismatched types ‘boost::adj_list_helper<Config, Base>’ and ‘boost::iterators::detail::iterator_facade_base<boost::range_detail::integer_iterator<long unsigned int>, long unsigned int, boost::iterators::random_access_traversal_tag, long unsigned int, long int, false, false>::reference {aka long unsigned int}’
put(mate, *vi, graph_traits<Graph>::null_vertex());
^
In file included from /usr/include/boost/graph/max_cardinality_matching.hpp:22:0,
from main.C:5:
/usr/include/boost/graph/filtered_graph.hpp:472:3: note: template<class G, class EP, class VP, class Property, class Key, class Value> void boost::put(Property, const boost::filtered_graph<Graph, EdgePredicate, VertexPredicate>&, const Key&, const Value&)
put(Property p, const filtered_graph<G, EP, VP>& g, const Key& k,
^
/usr/include/boost/graph/filtered_graph.hpp:472:3: note: template argument deduction/substitution failed:
In file included from main.C:5:0:
/usr/include/boost/graph/max_cardinality_matching.hpp:617:58: note: mismatched types ‘const boost::filtered_graph<Graph, EdgePredicate, VertexPredicate>’ and ‘boost::iterators::detail::iterator_facade_base<boost::range_detail::integer_iterator<long unsigned int>, long unsigned int, boost::iterators::random_access_traversal_tag, long unsigned int, long int, false, false>::reference {aka long unsigned int}’
put(mate, *vi, graph_traits<Graph>::null_vertex());
^
Full output here: http://pastebin.com/fG2aLRiG (Outsourced because of SO's restrictions on post length)

Answer 1

"A vector has all operations an array has" No. Arrays implicitly decay to pointers, vector does not. So when boost tries to pass it to the put function it generates this error:
error: no matching function for call to ‘put(std::vector<unsigned int>&, [blah blah])
note: candidates are:
template<class T, class V> void put(T*, std::ptrdiff_t, const V&)
template argument deduction/substitution failed:
mismatched types ‘T*’ and ‘std::vector<unsigned int>’
[followed by details about the other potential put functions]
Apperently the put function would accept one of these, or something that implicitly converts to one of these.
T*
boost::writable_property_map_archetype<K, V>&
const boost::put_get_helper<Reference, PropertyMap>&
boost::null_property_map<K, V>&
Property
(edmonds_maximum_cardinality_matching may have other requirements that cause these other types to also be invalid, I'm just saying these five types pass this particular hurdle.)

Answer 2

No, a std::vector does not have all these operations and won't convert to an array implicitly. Ignoring the fact that a std::array won't change that, for your purposes, it would be better suited.