From d8c6a552aae6c85226a6b918224f30b00fd4799f Mon Sep 17 00:00:00 2001
From: Andreas Schuh <andreas.schuh.84@gmail.com>
Date: Wed, 19 Mar 2014 11:29:43 +0000
Subject: [PATCH] Fix bug in SafeFOpen showing up in Cygwin. Errno only
 guaranteed to be set on failure.

---
 src/util.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/util.h b/src/util.h
index 9035890..339705e 100644
--- a/src/util.h
+++ b/src/util.h
@@ -364,7 +364,8 @@ inline int SafeFOpen(FILE **fp, const char* fname, const char *mode)
 #else
 	assert(fp != NULL);
 	*fp = fopen(fname, mode);
-	return errno;
+    // errno only guaranteed to be set on failure
+	return ((*fp == NULL) ? errno : 0);
 #endif
 }