From 6ec92ac5c0708786d2e904d9e41263f534147f8b Mon Sep 17 00:00:00 2001
From: Vitor Santos Costa <vsc@dcc.fc.up.pt>
Date: Sat, 19 Dec 2009 19:57:20 -0200
Subject: [PATCH] handle correctly file rewind in the presence of ungetc (obs
 from Jose Santos).

---
 C/iopreds.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/C/iopreds.c b/C/iopreds.c
index da4a75f97..7e93e55bc 100755
--- a/C/iopreds.c
+++ b/C/iopreds.c
@@ -3924,9 +3924,15 @@ static Int
 #if HAVE_FGETPOS
     fpos_t rpos;
 #endif
+    int ungetc_oldc = 0;
+    int had_ungetc = FALSE;
 
     /* two cases where we can seek: memory and console */
     if (seekable) {
+      if (Stream[inp_stream].stream_getc == PlUnGetc) {
+	had_ungetc = TRUE;
+	ungetc_oldc = Stream[inp_stream].och;
+      }
       if (Stream[inp_stream].status & InMemory_Stream_f) {
 	cpos = Stream[inp_stream].u.mem_string.pos;
       } else {
@@ -3946,6 +3952,10 @@ static Int
       if (Yap_Error_TYPE != YAP_NO_ERROR && seekable) {
 	H = old_H;
 	Yap_clean_tokenizer(tokstart, Yap_VarTable, Yap_AnonVarTable);
+	if (had_ungetc) {
+	  Stream[inp_stream].stream_getc = PlUnGetc;
+	  Stream[inp_stream].och = ungetc_oldc;
+	}
 	if (Stream[inp_stream].status & InMemory_Stream_f) {
 	  Stream[inp_stream].u.mem_string.pos = cpos;
 	} else {