Protect against an empty graph

diff --git a/lib/twopigen/twopiinit.c b/lib/twopigen/twopiinit.c
index eb85b86a320cdc1a3dfb0fdb23020420b3a9bff2..eced54419a964e916d7a1a32567e5d0a7a0e6efc 100644 (file)
--- a/lib/twopigen/twopiinit.c
+++ b/lib/twopigen/twopiinit.c
@@ -36,9 +36,11 @@ static void twopi_init_node_edge(graph_t * g)
     node_t *n;
     edge_t *e;
     int i = 0;
-    rdata* alg = N_NEW(agnnodes(g), rdata);
+    int n_nodes = agnnodes(g);
+    rdata* alg;
 
-    GD_neato_nlist(g) = N_NEW(agnnodes(g) + 1, node_t *);
+    alg = N_NEW(n_nodes, rdata);
+    GD_neato_nlist(g) = N_NEW(n_nodes + 1, node_t *);
     for (n = agfstnode(g); n; n = agnxtnode(g, n)) {
        neato_init_node(n);
        ND_alg(n) = alg + i;
@@ -67,6 +69,8 @@ void twopi_layout(Agraph_t * g)
     char *s;
     int setRoot = 0;
 
+    if (agnnodes(g) == 0) return;
+
     twopi_init_graph(g);
     s = agget(g, "root");
     if ((s = agget(g, "root"))) {
@@ -147,6 +151,7 @@ void twopi_cleanup(graph_t * g)
     edge_t *e;
 
     n = agfstnode (g);
+    if (!n) return; /* empty graph */
     free (ND_alg(n));
     for (; n; n = agnxtnode(g, n)) {
        for (e = agfstout(g, n); e; e = agnxtout(g, e)) {