From 3df8df47215da8bfcec3a3d1fd1785138911b402 Mon Sep 17 00:00:00 2001
From: erg <devnull@localhost>
Date: Wed, 9 Feb 2011 23:01:28 +0000
Subject: [PATCH] Protect against an empty graph

---
 lib/twopigen/twopiinit.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/lib/twopigen/twopiinit.c b/lib/twopigen/twopiinit.c
index eb85b86a3..eced54419 100644
--- 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)) {
-- 
2.40.0