5. Vertex iterators

5.1. igraph_vit_create — Creates a vertex iterator from a vertex selector.
5.2. igraph_vit_destroy — Destroys a vertex iterator.
5.3. Stepping over the vertices
5.4. IGRAPH_VIT_NEXT — Next vertex.
5.5. IGRAPH_VIT_END — Are we at the end?
5.6. IGRAPH_VIT_SIZE — Size of a vertex iterator.
5.7. IGRAPH_VIT_RESET — Reset a vertex iterator.
5.8. IGRAPH_VIT_GET — Query the current position.