What is a property map in BOOST?

Question

Can someone explain to a Boost beginner like me what is a property map is in Boost? I came across this when trying to use the BGL for calculating strong connected components. I

Answer 1

PropertyMaps at their core are an abstraction of data access. A problem that comes up very quickly in generic programming is: How do I get data associated with some object? It could be stored in the object itself, the object could be a pointer, it could be outside of the object in some mapping structure.

You can of course encapsulate data-access in a functor, but that becomes tedious very quickly and you look for a more narrow solution, the one chosen in Boost are PropertyMaps.

Remember this is just the concept. Concrete instances are for example an std::map (with some syntactic adaption), a function returning a member of the key (again, with some syntactic adaption).

Towards your edit: make_iterator_property_map builds an iterator_property_map. The first argument provides an iterator for a basis of offset calculations. The second argument is again a property_map to do the offset calculation. Together this provides a way to use an vertex_descriptor to write data to the vector based on the index of the vertex_descriptor.