int igraph_empty(igraph_t *graph, igraph_integer_t n, igraph_bool_t directed);

The most basic constructor, all the other constructors should call this to create a minimal graph object.

Arguments: 

Returns: 

Time complexity: O(|V|) for a graph with |V| vertices (and no edges).

int igraph_empty_attrs(igraph_t *graph, igraph_integer_t n, igraph_bool_t directed, void* attr);

Use this instead of igraph_empty() if you wish to add some graph attributes right after initialization. This function is currently not very interesting for the ordinary user, just supply 0 here or use igraph_empty().

Arguments: 

Returns: 

Time complexity: O(|V|) for a graph with |V| vertices (and no edges).

int igraph_copy(igraph_t *to, const igraph_t *from);

This function deeply copies a graph object to create an exact replica of it. The new replica should be destroyed by calling igraph_destroy() on it when not needed any more.

You can also create a shallow copy of a graph by simply using the standard assignment operator, but be careful and do not destroy a shallow replica. To avoid this mistake creating shallow copies is not recommended.

Arguments: 

Returns: 

Time complexity: O(|V|+|E|) for a graph with |V| vertices and |E| edges.

int igraph_destroy(igraph_t *graph);

This function should be called for every graph object exactly once.

This function invalidates all iterators (of course), but the iterators of are graph should be destroyed before the graph itself anyway.

Arguments: 

Returns: 

Time complexity: operating system specific.