Mixed graph (graphviz as a library)

Hello,
I use graphviz as a c++ library, and I need to create undirected edges in directed graph. How can I do this properly?
Thanks.

At the graph level, Graphviz

At the graph level, Graphviz does not support graphs with both directed and undirected edges. If the graph is directed and you create an edge using agedge(), it will be a directed edge. To have a notion of undirected edges, you can always attach an attribute to an edge, indicating that it is undirected. For drawing purposes, you can use dir=none. (http://www.graphviz.org/content/attrs#ddir and http://www.graphviz.org/content/attrs#kdirType)

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