diff --git a/smmapdfw/libsmmapdfw/dvl.h b/smmapdfw/libsmmapdfw/dvl.h
new file mode 100644
index 0000000..145aa2a
--- /dev/null
+++ b/smmapdfw/libsmmapdfw/dvl.h
@@ -0,0 +1,8 @@
+#ifndef _DVL_H_
+#define _DVL_H_
+
+#define dvl(a, b) (((a) == NULL) ? (b) : (a))
+#define dvls(a) dvl((a), "<NULL_STRING>")
+
+#endif
+