diff --git a/src/main.cpp b/src/main.cpp
@@ -484,7 +484,7 @@ static bool setup_log_params(const Settings &cmd_args)
 			color_mode = color_mode_env;
 #endif
 	}
-	if (color_mode != "") {
+	if (!color_mode.empty()) {
 		if (color_mode == "auto") {
 			Logger::color_mode = LOG_COLOR_AUTO;
 		} else if (color_mode == "always") {
@@ -586,7 +586,7 @@ static void startup_message()
 static bool read_config_file(const Settings &cmd_args)
 {
 	// Path of configuration file in use
-	sanity_check(g_settings_path == "");	// Sanity check
+	sanity_check(g_settings_path.empty());	// Sanity check
 
 	if (cmd_args.exists("config")) {
 		bool r = g_settings->readConfigFile(cmd_args.get("config").c_str());
@@ -793,7 +793,7 @@ static bool auto_select_world(GameParams *game_params)
 		           << world_path << "]" << std::endl;
 	}
 
-	assert(world_path != "");	// Post-condition
+	assert(!world_path.empty());	// Post-condition
 	game_params->world_path = world_path;
 	return true;
 }
@@ -849,7 +849,7 @@ static bool determine_subgame(GameParams *game_params)
 {
 	SubgameSpec gamespec;
 
-	assert(game_params->world_path != "");	// Pre-condition
+	assert(!game_params->world_path.empty());	// Pre-condition
 
 	// If world doesn't exist
 	if (!game_params->world_path.empty()

diff --git a/src/map.cpp b/src/map.cpp
@@ -533,7 +533,7 @@ void ServerMap::transformLiquids(std::map<v3s16, MapBlock*> &modified_blocks,
 		infostream<<"transformLiquids(): initial_size="<<initial_size<<std::endl;*/
 
 	// list of nodes that due to viscosity have not reached their max level height
-	std::deque<v3s16> must_reflow;
+	std::vector<v3s16> must_reflow;
 
 	std::vector<std::pair<v3s16, MapNode> > changed_nodes;
 
@@ -835,7 +835,7 @@ void ServerMap::transformLiquids(std::map<v3s16, MapBlock*> &modified_blocks,
 	}
 	//infostream<<"Map::transformLiquids(): loopcount="<<loopcount<<std::endl;
 
-	for (auto &iter : must_reflow)
+	for (const auto &iter : must_reflow)
 		m_transforming_liquid.push_back(iter);
 
 	voxalgo::update_lighting_nodes(this, changed_nodes, modified_blocks);

diff --git a/src/mapgen/mg_schematic.cpp b/src/mapgen/mg_schematic.cpp
@@ -234,7 +234,6 @@ bool Schematic::placeOnVManip(MMVManip *vm, v3s16 p, u32 flags,
 void Schematic::placeOnMap(ServerMap *map, v3s16 p, u32 flags,
 	Rotation rot, bool force_place)
 {
-	std::map<v3s16, MapBlock *> lighting_modified_blocks;
 	std::map<v3s16, MapBlock *> modified_blocks;
 	std::map<v3s16, MapBlock *>::iterator it;
 

diff --git a/src/network/clientpackethandler.cpp b/src/network/clientpackethandler.cpp
@@ -152,7 +152,7 @@ void Client::handleCommand_AuthAccept(NetworkPacket* pkt)
 	language code (e.g. "de" for German). */
 	std::string lang = gettext("LANG_CODE");
 	if (lang == "LANG_CODE")
-		lang = "";
+		lang.clear();
 
 	NetworkPacket resp_pkt(TOSERVER_INIT2, sizeof(u16) + lang.size());
 	resp_pkt << lang;

diff --git a/src/network/connection.cpp b/src/network/connection.cpp
@@ -64,7 +64,7 @@ BufferedPacketPtr makePacket(Address &address, const SharedBuffer<u8> &data,
 {
 	u32 packet_size = data.getSize() + BASE_HEADER_SIZE;
 
-	BufferedPacketPtr p(new BufferedPacket(packet_size));
+	auto p = std::make_shared<BufferedPacket>(packet_size);
 	p->address = address;
 
 	writeU32(&p->data[0], protocol_id);
@@ -492,10 +492,10 @@ SharedBuffer<u8> IncomingSplitBuffer::insert(BufferedPacketPtr &p_ptr, bool reli
 
 void IncomingSplitBuffer::removeUnreliableTimedOuts(float dtime, float timeout)
 {
-	std::deque<u16> remove_queue;
+	std::vector<u16> remove_queue;
 	{
 		MutexAutoLock listlock(m_map_mutex);
-		for (auto &i : m_buf) {
+		for (const auto &i : m_buf) {
 			IncomingSplitPacket *p = i.second;
 			// Reliable ones are not removed by timeout
 			if (p->reliable)

diff --git a/src/nodedef.cpp b/src/nodedef.cpp
@@ -354,12 +354,12 @@ void ContentFeatures::reset()
 		NOTE: Most of this is always overridden by the default values given
 		      in builtin.lua
 	*/
-	name = "";
+	name.clear();
 	groups.clear();
 	// Unknown nodes can be dug
 	groups["dig_immediate"] = 2;
 	drawtype = NDT_NORMAL;
-	mesh = "";
+	mesh.clear();
 #ifndef SERVER
 	for (auto &i : mesh_ptr)
 		i = NULL;
@@ -387,9 +387,9 @@ void ContentFeatures::reset()
 	leveled = 0;
 	leveled_max = LEVELED_MAX;
 	liquid_type = LIQUID_NONE;
-	liquid_alternative_flowing = "";
+	liquid_alternative_flowing.clear();
 	liquid_alternative_flowing_id = CONTENT_IGNORE;
-	liquid_alternative_source = "";
+	liquid_alternative_source.clear();
 	liquid_alternative_source_id = CONTENT_IGNORE;
 	liquid_viscosity = 0;
 	liquid_renewable = true;
@@ -410,7 +410,7 @@ void ContentFeatures::reset()
 	connects_to_ids.clear();
 	connect_sides = 0;
 	color = video::SColor(0xFFFFFFFF);
-	palette_name = "";
+	palette_name.clear();
 	palette = NULL;
 	node_dig_prediction = "air";
 	move_resistance = 0;
@@ -1355,7 +1355,7 @@ void NodeDefManager::eraseIdFromGroups(content_t id)
 content_t NodeDefManager::set(const std::string &name, const ContentFeatures &def)
 {
 	// Pre-conditions
-	assert(name != "");
+	assert(!name.empty());
 	assert(name != "ignore");
 	assert(name == def.name);
 
@@ -1395,7 +1395,7 @@ content_t NodeDefManager::set(const std::string &name, const ContentFeatures &de
 
 content_t NodeDefManager::allocateDummy(const std::string &name)
 {
-	assert(name != "");	// Pre-condition
+	assert(!name.empty());	// Pre-condition
 	ContentFeatures f;
 	f.name = name;
 	return set(name, f);
@@ -1405,7 +1405,7 @@ content_t NodeDefManager::allocateDummy(const std::string &name)
 void NodeDefManager::removeNode(const std::string &name)
 {
 	// Pre-condition
-	assert(name != "");
+	assert(!name.empty());
 
 	// Erase name from name ID mapping
 	content_t id = CONTENT_IGNORE;

diff --git a/src/nodetimer.h b/src/nodetimer.h
@@ -93,15 +93,11 @@ class NodeTimerList
 		}
 	}
 	// Undefined behaviour if there already is a timer
-	void insert(NodeTimer timer) {
+	void insert(const NodeTimer &timer) {
 		v3s16 p = timer.position;
 		double trigger_time = m_time + (double)(timer.timeout - timer.elapsed);
-		std::multimap<double, NodeTimer>::iterator it =
-			m_timers.insert(std::pair<double, NodeTimer>(
-				trigger_time, timer
-			));
-		m_iterators.insert(
-			std::pair<v3s16, std::multimap<double, NodeTimer>::iterator>(p, it));
+		std::multimap<double, NodeTimer>::iterator it = m_timers.emplace(trigger_time, timer);
+		m_iterators.emplace(p, it);
 		if (m_next_trigger_time == -1. || trigger_time < m_next_trigger_time)
 			m_next_trigger_time = trigger_time;
 	}

diff --git a/src/script/common/c_content.cpp b/src/script/common/c_content.cpp
@@ -481,7 +481,7 @@ TileDef read_tiledef(lua_State *L, int index, u8 drawtype)
 	else if(lua_istable(L, index))
 	{
 		// name="default_lava.png"
-		tiledef.name = "";
+		tiledef.name.clear();
 		getstringfield(L, index, "name", tiledef.name);
 		getstringfield(L, index, "image", tiledef.name); // MaterialSpec compat.
 		tiledef.backface_culling = getboolfield_default(

diff --git a/src/script/cpp_api/s_base.cpp b/src/script/cpp_api/s_base.cpp
@@ -171,7 +171,7 @@ void ScriptApiBase::clientOpenLibs(lua_State *L)
 #endif
 	};
 
-	for (const std::pair<std::string, lua_CFunction> &lib : m_libs) {
+	for (const auto &lib : m_libs) {
 	    lua_pushcfunction(L, lib.second);
 	    lua_pushstring(L, lib.first.c_str());
 	    lua_call(L, 1, 0);

diff --git a/src/script/lua_api/l_client.cpp b/src/script/lua_api/l_client.cpp
@@ -237,7 +237,7 @@ int ModApiClient::l_get_language(lua_State *L)
 #endif
 	std::string lang = gettext("LANG_CODE");
 	if (lang == "LANG_CODE")
-		lang = "";
+		lang.clear();
 
 	lua_pushstring(L, locale);
 	lua_pushstring(L, lang.c_str());

diff --git a/src/script/lua_api/l_item.cpp b/src/script/lua_api/l_item.cpp
@@ -600,7 +600,7 @@ int ModApiItemMod::l_register_item_raw(lua_State *L)
 		if(def.type == ITEM_NODE)
 			def.node_placement_prediction = name;
 		else
-			def.node_placement_prediction = "";
+			def.node_placement_prediction.clear();
 	}
 
 	// Register item definition

diff --git a/src/server.cpp b/src/server.cpp
@@ -424,7 +424,7 @@ void Server::init()
 	m_mod_storage_database->beginSave();
 
 	m_modmgr = std::make_unique<ServerModManager>(m_path_world);
-	std::vector<ModSpec> unsatisfied_mods = m_modmgr->getUnsatisfiedMods();
+
 	// complain about mods with unsatisfied dependencies
 	if (!m_modmgr->isConsistent()) {
 		std::string error = m_modmgr->getUnsatisfiedModsError();
@@ -1359,8 +1359,6 @@ void Server::Send(session_t peer_id, NetworkPacket *pkt)
 
 void Server::SendMovement(session_t peer_id)
 {
-	std::ostringstream os(std::ios_base::binary);
-
 	NetworkPacket pkt(TOCLIENT_MOVEMENT, 12 * sizeof(float), peer_id);
 
 	pkt << g_settings->getFloat("movement_acceleration_default");

diff --git a/src/tool.cpp b/src/tool.cpp
@@ -35,7 +35,7 @@ void ToolGroupCap::toJson(Json::Value &object) const
 	Json::Value times_object;
 	for (auto time : times)
 		times_object[time.first] = time.second;
-	object["times"] = times_object;
+	object["times"] = std::move(times_object);
 }
 
 void ToolGroupCap::fromJson(const Json::Value &json)
@@ -134,14 +134,13 @@ void ToolCapabilities::serializeJson(std::ostream &os) const
 	for (const auto &groupcap : groupcaps) {
 		groupcap.second.toJson(groupcaps_object[groupcap.first]);
 	}
-	root["groupcaps"] = groupcaps_object;
+	root["groupcaps"] = std::move(groupcaps_object);
 
 	Json::Value damage_groups_object;
-	DamageGroup::const_iterator dgiter;
-	for (dgiter = damageGroups.begin(); dgiter != damageGroups.end(); ++dgiter) {
-		damage_groups_object[dgiter->first] = dgiter->second;
+	for (const auto &damagegroup : damageGroups) {
+		damage_groups_object[damagegroup.first] = damagegroup.second;
 	}
-	root["damage_groups"] = damage_groups_object;
+	root["damage_groups"] = std::move(damage_groups_object);
 
 	fastWriteJson(root, os);
 }

diff --git a/src/unittest/test_filepath.cpp b/src/unittest/test_filepath.cpp
@@ -238,7 +238,7 @@ void TestFilePath::testRemoveLastPathComponentWithTrailingDelimiter()
 
 void TestFilePath::testRemoveRelativePathComponent()
 {
-	std::string path, result, removed;
+	std::string path, result;
 
 	path = p("/home/user/minetest/bin");
 	result = fs::RemoveRelativePathComponents(path);

diff --git a/src/unittest/test_modmetadatadatabase.cpp b/src/unittest/test_modmetadatadatabase.cpp
@@ -206,7 +206,6 @@ void TestModMetadataDatabase::testRecallFail()
 void TestModMetadataDatabase::testCreate()
 {
 	ModMetadataDatabase *mod_meta_db = mod_meta_provider->getModMetadataDatabase();
-	StringMap recalled;
 	UASSERT(mod_meta_db->setModEntry("mod1", "key1", "value1"));
 }
 
@@ -222,7 +221,6 @@ void TestModMetadataDatabase::testRecall()
 void TestModMetadataDatabase::testChange()
 {
 	ModMetadataDatabase *mod_meta_db = mod_meta_provider->getModMetadataDatabase();
-	StringMap recalled;
 	UASSERT(mod_meta_db->setModEntry("mod1", "key1", "value2"));
 }
 

diff --git a/src/util/quicktune_shortcutter.h b/src/util/quicktune_shortcutter.h
@@ -36,7 +36,7 @@ class QuicktuneShortcutter
 	std::string getMessage()
 	{
 		std::string s = m_message;
-		m_message = "";
+		m_message.clear();
 		if (!s.empty())
 			return std::string("[quicktune] ") + s;
 		return "";

diff --git a/src/util/string.h b/src/util/string.h
@@ -610,7 +610,7 @@ std::vector<std::basic_string<T> > split(const std::basic_string<T> &s, T delim)
 		} else {
 			if (si == delim) {
 				tokens.push_back(current);
-				current = std::basic_string<T>();
+				current.clear();
 				last_was_escape = false;
 			} else if (si == '\\') {
 				last_was_escape = true;