Adding and removing existing edge in a graph (BOOST)?

Question

Lets say I have an undirected graph G. Lets say I add the following

add_edge(1,2,G);
add_edge(1,3,G);
add_edge(0,2,G);

Now I lets say add this again:

add_edge(0,2,G);

Do I have two edges in my graph from 0 ---> 2 ?

What happens if I added the edge twice and I do:

remove_edge(0,2,G);

Do both the edges disappear,or do I still have one of them?

Answer 1

The answer to both of your questions depends on the definition of graph G.

The answer to the first question, according to the boost::graph tutorial, depends on which OutEdgeList you use in your graph definition. If you use a container that cannot represent multiple edges (such as setS or hash_setS), there will be only one edge between two vertices no matter how many times you insert it. If you use a vectorS, multisetS or similar, there will be one edge inserted for each call of add_edge().

The answer to the second question, according to the same page (that section of the page does not allow direct links - just search for remove_edge) is that all edges between the two vertices will be removed after calling that particular remove_edge() function. There are several other versions of remove_edge() (described on the same page), each with a slightly different behaviour.