Pass strings by constref when possible

These instances were found by cppcheck.
Thanks matthiaskrgr for running it.

src/carryover.cpp

@@ -163,7 +163,7 @@ void carryover_info::remove_side(const std::string& id) {
 
 struct save_id_equals
 {
-	save_id_equals(std::string val) : value (val) {}
+	save_id_equals(const std::string& val) : value (val) {}
 	bool operator () (carryover& v2)
 	{
 		return value == v2.get_save_id();
@@ -250,7 +250,7 @@ const config carryover_info::to_config()
 	return cfg;
 }
 
-carryover* carryover_info::get_side(std::string save_id){
+carryover* carryover_info::get_side(const std::string& save_id){
 	for(carryover& side : carryover_sides_) {
 		if(side.get_save_id() == save_id){
 			return &side;

src/carryover.hpp

@@ -65,7 +65,7 @@ public:
 	/// @param from_snapshot true if cfg is a [snapshot], false if cfg is [carryover_sides(_start)]
 	explicit carryover_info(const config& cfg, bool from_snapshot = false);
 
-	carryover* get_side(std::string save_id);
+	carryover* get_side(const std::string& save_id);
 	std::vector<carryover>& get_all_sides();
 	void add_side(const config& cfg);
 	void add_side(const team& t, const int gold, const bool add);

src/filesystem.hpp

@@ -82,7 +82,7 @@ std::string get_addons_dir();
  * maximum 1000 files then start always giving 999
  */
 std::string get_next_filename(const std::string& name, const std::string& extension);
-void set_user_config_dir(std::string path);
+void set_user_config_dir(const std::string& path);
 void set_user_data_dir(std::string path);
 
 std::string get_user_config_dir();

src/filesystem_boost.cpp

@@ -594,7 +594,7 @@ static void set_user_config_path(path newconfig)
 	}
 }
 
-void set_user_config_dir(std::string newconfigdir)
+void set_user_config_dir(const std::string& newconfigdir)
 {
 	set_user_config_path(newconfigdir);
 }

src/font/error.hpp

@@ -21,7 +21,7 @@
 namespace font {
 
 struct error : public game::error {
-	error(std::string str = "Font initialization failed") : game::error(str) {}
+	error(const std::string& str = "Font initialization failed") : game::error(str) {}
 };
 
 } // end namespace font

src/game_launcher.hpp

@@ -33,7 +33,7 @@ namespace savegame { struct load_game_metadata; }
 struct jump_to_campaign_info
 {
 public:
-	jump_to_campaign_info(bool jump,int difficulty, std::string campaign_id,std::string scenario_id)
+	jump_to_campaign_info(bool jump,int difficulty, const std::string& campaign_id,const std::string& scenario_id)
 		: jump_(jump)
 		, difficulty_(difficulty)
 		, campaign_id_(campaign_id)

src/generic_event.cpp

@@ -18,7 +18,7 @@
 
 namespace events{
 
-generic_event::generic_event(std::string name) :
+generic_event::generic_event(const std::string& name) :
 	name_(name),
 	observers_(),
 	change_handler_(false),

src/generic_event.hpp

@@ -43,7 +43,7 @@ This is the class that notifies the observers and maintains a list of them.
 */
 class generic_event{
 public:
-	generic_event(std::string name);
+	generic_event(const std::string& name);
 	virtual ~generic_event() {}
 
 	virtual bool attach_handler(observer* obs);

src/gui/dialogs/gamestate_inspector.cpp

@@ -191,7 +191,7 @@ public:
 	{
 	}
 
-	stuff_list_adder stuff_list_entry(tree_view_node* parent, const std::string defn)
+	stuff_list_adder stuff_list_entry(tree_view_node* parent, const std::string& defn)
 	{
 		return stuff_list_adder(parent ? *parent : stuff_list_->get_root_node(), defn);
 	}

src/gui/dialogs/lua_interpreter.cpp

@@ -223,7 +223,7 @@ public:
 		} catch (...) { std::cerr << "Swallowed an exception when trying to write lua command line history\n";}
 	}
 #endif
-	void add_to_history (std::string str) {
+	void add_to_history (const std::string& str) {
 		prefix_ = "";
 		(void) str;
 #ifdef HAVE_HISTORY

src/hotkey/hotkey_item.cpp

@@ -445,7 +445,7 @@ void save_hotkeys(config& cfg)
 	}
 }
 
-std::string get_names(std::string id)
+std::string get_names(const std::string& id)
 {
 	// Names are used in places like the hot-key preferences menu
 	std::vector<std::string> names;

src/hotkey/hotkey_item.hpp

@@ -421,7 +421,7 @@ void clear_hotkeys();
  * "ctrl+l" or "n" or "mouse 1". The comman separated string is of the form "ctrl+l,n,mouse 1".
  * @return The comma separated string of hotkey names.
  */
-std::string get_names(std::string id);
+std::string get_names(const std::string& id);
 
 /**
  * Save the non-default hotkeys to the config.

src/image_modifications.hpp

@@ -431,7 +431,7 @@ private:
 class scale_modification : public modification
 {
 public:
-	scale_modification(int width, int height, std::string fn, bool use_nn)
+	scale_modification(int width, int height, const std::string& fn, bool use_nn)
 		: w_(width), h_(height), nn_(use_nn), fn_(fn)
 	{}
 	virtual surface operator()(const surface& src) const;
@@ -461,7 +461,7 @@ protected:
 class scale_exact_modification : public scale_modification
 {
 public:
-	scale_exact_modification(int width, int height, std::string fn, bool use_nn)
+	scale_exact_modification(int width, int height, const std::string& fn, bool use_nn)
 		: scale_modification(width, height, fn, use_nn)
 	{}
 	virtual std::pair<int,int> calculate_size(const surface& src) const;
@@ -474,7 +474,7 @@ public:
 class scale_into_modification : public scale_modification
 {
 public:
-	scale_into_modification(int width, int height, std::string fn, bool use_nn)
+	scale_into_modification(int width, int height, const std::string& fn, bool use_nn)
 		: scale_modification(width, height, fn, use_nn)
 	{}
 	virtual std::pair<int,int> calculate_size(const surface& src) const;

src/mp_ui_alerts.cpp

@@ -33,17 +33,17 @@ namespace mp_ui_alerts {
 
 namespace {
 
-bool lobby_pref(std::string id)
+bool lobby_pref(const std::string& id)
 {
 	return preferences::get(id + "_lobby", get_def_pref_lobby(id));
 }
 
-bool sound_pref(std::string id)
+bool sound_pref(const std::string& id)
 {
 	return preferences::get(id + "_sound", get_def_pref_sound(id));
 }
 
-bool notif_pref(std::string id)
+bool notif_pref(const std::string& id)
 {
 	return preferences::get(id + "_notif", get_def_pref_notif(id));
 }

src/scripting/lua_unit_attacks.cpp

@@ -85,7 +85,7 @@ using attack_ptr_in = boost::intrusive_ptr<typename utils::const_clone<attack_ty
 
 // Note that these two templates are designed on the assumption that T is either unit or unit_type
 template<typename T>
-auto find_attack(T* u, std::string id) -> attack_ptr_in<T>
+auto find_attack(T* u, const std::string& id) -> attack_ptr_in<T>
 {
 	auto attacks = u->attacks();
 	for(auto at = attacks.begin(); at != attacks.end(); ++at) {

src/serialization/preprocessor.cpp

@@ -1349,7 +1349,7 @@ std::istream *preprocess_file(const std::string& fname, preproc_map *defines)
 }
 
 void preprocess_resource(const std::string& res_name, preproc_map *defines_map,
-			 bool write_cfg, bool write_plain_cfg,std::string target_directory)
+			 bool write_cfg, bool write_plain_cfg,const std::string& target_directory)
 {
 	if (filesystem::is_directory(res_name))
 	{

src/serialization/preprocessor.hpp

@@ -75,6 +75,6 @@ std::ostream& operator<<(std::ostream& stream, const preproc_map::value_type& de
 std::istream *preprocess_file(const std::string& fname, preproc_map *defines = nullptr);
 
 void preprocess_resource(const std::string& res_name, preproc_map *defines_map,
-			bool write_cfg=false, bool write_plain_cfg=false, std::string target_directory="");
+			bool write_cfg=false, bool write_plain_cfg=false, const std::string& target_directory="");
 
 #endif

src/serialization/string_utils.cpp

@@ -502,7 +502,7 @@ static void si_string_impl_stream_write(std::stringstream &ss, double input) {
 	ss.precision(oldprec);
 }
 
-std::string si_string(double input, bool base2, std::string unit) {
+std::string si_string(double input, bool base2, const std::string& unit) {
 	const double multiplier = base2 ? 1024 : 1000;
 
 	typedef std::array<std::string, 9> strings9;

src/serialization/string_utils.hpp

@@ -281,7 +281,7 @@ inline std::string signed_percent(int val) {return signed_value(val) + "%";}
  *
  * There are no default values because they would not be translatable.
  */
-std::string si_string(double input, bool base2, std::string unit);
+std::string si_string(double input, bool base2, const std::string& unit);
 
 /**
  * Try to complete the last word of 'text' with the 'wordlist'.

src/synced_user_choice.cpp

@@ -222,7 +222,7 @@ config mp_sync::get_user_choice(const std::string &name, const mp_sync::user_cho
 	return retv[side];
 }
 
-user_choice_manager::user_choice_manager(const std::string &name, const mp_sync::user_choice &uch, std::set<int> sides)
+user_choice_manager::user_choice_manager(const std::string &name, const mp_sync::user_choice &uch, const std::set<int>& sides)
 	: required_(sides)
 	, res_()
 	, local_choice_(0)

src/synced_user_choice.hpp

@@ -89,7 +89,7 @@ class user_choice_manager : events::pump_monitor
 	const std::string& tagname_;
 	const int current_side_;
 	// private constructor, this object is only constructed by user_choice_manager::get_user_choice_internal
-	user_choice_manager(const std::string &name, const mp_sync::user_choice &uch, std::set<int> sides);
+	user_choice_manager(const std::string &name, const mp_sync::user_choice &uch, const std::set<int>& sides);
 	~user_choice_manager() {}
 	void search_in_replay();
 public:

src/theme.cpp

@@ -781,7 +781,7 @@ void theme::add_object(const config& cfg)
 	}
 }
 
-void theme::remove_object(std::string id){
+void theme::remove_object(const std::string& id){
 	for(std::vector<theme::panel>::iterator p = panels_.begin(); p != panels_.end(); ++p) {
 		if (p->get_id() == id){
 			panels_.erase(p);
@@ -873,7 +873,7 @@ void theme::modify(const config &cfg)
 	}
 }
 
-theme::object& theme::find_element(std::string id){
+theme::object& theme::find_element(const std::string& id){
 	static theme::object empty_object;
 	theme::object* res = &empty_object;
 	for (std::vector<theme::panel>::iterator p = panels_.begin(); p != panels_.end(); ++p){

src/theme.hpp

@@ -294,9 +294,9 @@ public:
 	events::generic_event& theme_reset_event() { return theme_reset_event_; }
 
 private:
-	theme::object& find_element(std::string id);
+	theme::object& find_element(const std::string& id);
 	void add_object(const config& cfg);
-	void remove_object(std::string id);
+	void remove_object(const std::string& id);
 	void set_object_location(theme::object& element, std::string rect_str, std::string ref_id);
 
 	//notify observers that the theme has been rebuilt completely

src/units/udisplay.cpp

@@ -572,7 +572,7 @@ void unit_die(const map_location& loc, unit& loser,
 void unit_attack(display * disp, game_board & board,
                  const map_location& a, const map_location& b, int damage,
                  const attack_type& attack, const attack_type* secondary_attack,
-                 int swing,std::string hit_text,int drain_amount,std::string att_text, const std::vector<std::string>* extra_hit_sounds)
+                 int swing,const std::string& hit_text,int drain_amount,const std::string& att_text, const std::vector<std::string>* extra_hit_sounds)
 {
 	if(!disp ||disp->video().update_locked() || disp->video().faked() ||
 			(disp->fogged(a) && disp->fogged(b)) || preferences::show_combat() == false) {

src/units/udisplay.hpp

@@ -120,7 +120,7 @@ void unit_sheath_weapon( const map_location& loc, unit* u=nullptr, const attack_
 void unit_attack(display * disp, game_board & board, //TODO: Would be nice if this could be purely a display function and defer damage dealing to its caller
 	const map_location& a, const map_location& b, int damage,
 	const attack_type& attack, const attack_type* secondary_attack,
-	int swing, std::string hit_text, int drain_amount, std::string att_text, const std::vector<std::string>* extra_hit_sounds=nullptr);
+	int swing, const std::string& hit_text, int drain_amount, const std::string& att_text, const std::vector<std::string>* extra_hit_sounds=nullptr);
 
 
 void unit_recruited(const map_location& loc,