pub unsafe extern "C" fn igraph_diameter(
graph: *const igraph_t,
weights: *const igraph_vector_t,
res: *mut igraph_real_t,
from: *mut igraph_int_t,
to: *mut igraph_int_t,
vertex_path: *mut igraph_vector_int_t,
edge_path: *mut igraph_vector_int_t,
directed: igraph_bool_t,
unconn: igraph_bool_t,
) -> igraph_error_t