Add extra "const"

cache.cpp

@@ -22,7 +22,7 @@ float Cache::distance() const {
 	return 2 * Earth_radius * asin(sqrt(pow(sin(degtorad((pos.lat - home.lat) / 2)), 2) + cos(degtorad(pos.lat)) * cos(degtorad(home.lat)) * pow(sin(degtorad((pos.lon - home.lon) / 2)), 2)));
 }
 
-void Cache::set_date(std::tm* t) {
+void Cache::set_date(const std::tm* t) {
 	char tmp[20];
 
 	date_tm = *t;

cache.h

@@ -62,7 +62,7 @@ public:
 	std::string day_of_week;
 	std::string date;
 
-	void set_date(std::tm* t);
+	void set_date(const std::tm* t);
 
 	static Position home;