Include string.h
--- a/CalcEphem.h
+++ b/CalcEphem.h
@@ -13,6 +13,7 @@
 #include <glib.h>
 
 #include <stdio.h>
+#include <string.h>
 #include <math.h>
 
 #define DegPerRad       57.29577951308232087680
-- 
2.34.1