53 files changed, 305 insertions, 385 deletions

diff --git a/src/Bindings/CMakeLists.txt b/src/Bindings/CMakeLists.txt
index 004d8be30..7aaa5f3a6 100644
--- a/src/Bindings/CMakeLists.txt
+++ b/src/Bindings/CMakeLists.txt
@@ -176,5 +176,5 @@ endif()
 
 if(NOT MSVC)
 	add_library(Bindings ${SRCS} ${HDRS})
-	target_link_libraries(Bindings lua sqlite tolualib mbedtls HTTPServer)
+	target_link_libraries(Bindings fmt::fmt lua sqlite tolualib mbedtls HTTPServer)
 endif()
diff --git a/src/Bindings/LuaState.cpp b/src/Bindings/LuaState.cpp
index 095322bdd..f16b77dc8 100644
--- a/src/Bindings/LuaState.cpp
+++ b/src/Bindings/LuaState.cpp
@@ -2004,7 +2004,7 @@ void cLuaState::LogStackTrace(lua_State * a_LuaState, int a_StartingDepth)
 
 
 
-int cLuaState::ApiParamError(const char * a_MsgFormat, ...)
+int cLuaState::ApiParamError(const char * a_MsgFormat, fmt::ArgList argp)
 {
 	// Retrieve current function name
 	lua_Debug entry;
@@ -2012,23 +2012,8 @@ int cLuaState::ApiParamError(const char * a_MsgFormat, ...)
 	VERIFY(lua_getinfo(m_LuaState, "n", &entry));
 
 	// Compose the error message:
-	va_list argp;
-	va_start(argp, a_MsgFormat);
-	AString msg;
-
-	#ifdef __clang__
-		#pragma clang diagnostic push
-		#pragma clang diagnostic ignored "-Wformat-nonliteral"
-	#endif
-
-	AppendVPrintf(msg, a_MsgFormat, argp);
-
-	#ifdef __clang__
-		#pragma clang diagnostic pop
-	#endif
-
-	va_end(argp);
-	AString errorMsg = Printf("%s: %s", (entry.name != nullptr) ? entry.name : "<unknown function>", msg.c_str());
+	AString msg = Printf(a_MsgFormat, argp);
+	AString errorMsg = fmt::format("{0}: {1}", (entry.name != nullptr) ? entry.name : "<unknown function>", msg);
 
 	// Log everything into the console:
 	LOGWARNING("%s", errorMsg.c_str());
diff --git a/src/Bindings/LuaState.h b/src/Bindings/LuaState.h
index 60af36228..2510c6f0b 100644
--- a/src/Bindings/LuaState.h
+++ b/src/Bindings/LuaState.h
@@ -823,7 +823,8 @@ public:
 	/** Formats and prints the message, prefixed with the current function name, then logs the stack contents and raises a Lua error.
 	To be used for bindings when they detect bad parameters.
 	Doesn't return, but a dummy return type is provided so that Lua API functions may do "return ApiParamError(...)". */
-	int ApiParamError(const char * a_MsgFormat, ...);
+	int ApiParamError(const char * a_MsgFormat, fmt::ArgList);
+	FMT_VARIADIC(int, ApiParamError, const char *)
 
 	/** Returns the type of the item on the specified position in the stack */
 	AString GetTypeText(int a_StackPos);
diff --git a/src/Bindings/ManualBindings.cpp b/src/Bindings/ManualBindings.cpp
index 7dd724d44..4e7d7c8ef 100644
--- a/src/Bindings/ManualBindings.cpp
+++ b/src/Bindings/ManualBindings.cpp
@@ -116,7 +116,7 @@ int cManualBindings::tolua_do_error(lua_State * L, const char * a_pMsg, tolua_Er
 
 
 
-int cManualBindings::lua_do_error(lua_State * L, const char * a_pFormat, ...)
+int cManualBindings::lua_do_error(lua_State * L, const char * a_pFormat, fmt::ArgList a_ArgList)
 {
 	// Retrieve current function name
 	lua_Debug entry;
@@ -128,11 +128,9 @@ int cManualBindings::lua_do_error(lua_State * L, const char * a_pFormat, ...)
 	ReplaceString(msg, "#funcname#", (entry.name != nullptr) ? entry.name : "?");
 
 	// Copied from luaL_error and modified
-	va_list argp;
-	va_start(argp, a_pFormat);
 	luaL_where(L, 1);
-	lua_pushvfstring(L, msg.c_str(), argp);
-	va_end(argp);
+	AString FmtMsg = Printf(msg.c_str(), a_ArgList);
+	lua_pushlstring(L, FmtMsg.data(), FmtMsg.size());
 	lua_concat(L, 2);
 	return lua_error(L);
 }
diff --git a/src/Bindings/ManualBindings.h b/src/Bindings/ManualBindings.h
index cfdca7597..fb19d5a61 100644
--- a/src/Bindings/ManualBindings.h
+++ b/src/Bindings/ManualBindings.h
@@ -50,7 +50,8 @@ public:
 	// Helper functions:
 	static cPluginLua * GetLuaPlugin(lua_State * L);
 	static int tolua_do_error(lua_State * L, const char * a_pMsg, tolua_Error * a_pToLuaError);
-	static int lua_do_error(lua_State * L, const char * a_pFormat, ...);
+	static int lua_do_error(lua_State * L, const char * a_pFormat, fmt::ArgList a_ArgList);
+	FMT_VARIADIC(static int, lua_do_error, lua_State *, const char *)
 
 
 	/** Binds the DoWith(ItemName) functions of regular classes. */
diff --git a/src/BlockEntities/CMakeLists.txt b/src/BlockEntities/CMakeLists.txt
index d512a776c..f3d0beb55 100644
--- a/src/BlockEntities/CMakeLists.txt
+++ b/src/BlockEntities/CMakeLists.txt
@@ -48,4 +48,5 @@ SET (HDRS
 
 if(NOT MSVC)
 	add_library(BlockEntities ${SRCS} ${HDRS})
+	target_link_libraries(BlockEntities fmt::fmt)
 endif()
diff --git a/src/Blocks/CMakeLists.txt b/src/Blocks/CMakeLists.txt
index 496ec69e4..07ab87eea 100644
--- a/src/Blocks/CMakeLists.txt
+++ b/src/Blocks/CMakeLists.txt
@@ -104,4 +104,5 @@ SET (HDRS
 
 if(NOT MSVC)
 	add_library(Blocks ${SRCS} ${HDRS})
+	target_link_libraries(Blocks fmt::fmt)
 endif()
diff --git a/src/BrewingRecipes.cpp b/src/BrewingRecipes.cpp
index 15e9826de..292fc7005 100644
--- a/src/BrewingRecipes.cpp
+++ b/src/BrewingRecipes.cpp
@@ -55,7 +55,7 @@ void cBrewingRecipes::ReloadRecipes(void)
 		AddRecipeFromLine(ParsingLine, LineNum);
 	}  // while (getline(ParsingLine))
 
-	LOG("Loaded " SIZE_T_FMT " brewing recipes", m_Recipes.size());
+	LOG("Loaded %zu brewing recipes", m_Recipes.size());
 }
 
 
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index c023889bc..b5daedfaa 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -124,6 +124,7 @@ SET (HDRS
 	LinearUpscale.h
 	Logger.h
 	LoggerListeners.h
+	LoggerSimple.h
 	Map.h
 	MapManager.h
 	Matrix4.h
@@ -359,7 +360,7 @@ if (${CMAKE_SYSTEM_NAME} STREQUAL "FreeBSD")
 	add_flags_lnk(-L/usr/ports/devel)
 endif()
 
-target_link_libraries(${CMAKE_PROJECT_NAME} luaexpat jsoncpp_lib_static mbedtls zlib sqlite lua SQLiteCpp event_core event_extra)
+target_link_libraries(${CMAKE_PROJECT_NAME} luaexpat jsoncpp_lib_static mbedtls zlib sqlite lua SQLiteCpp event_core event_extra fmt::fmt)
 
 # Create a folder for Bindings' documentation:
 FILE(MAKE_DIRECTORY "Bindings/docs")
diff --git a/src/ClientHandle.cpp b/src/ClientHandle.cpp
index 7fb4ca1a9..8470e7de6 100644
--- a/src/ClientHandle.cpp
+++ b/src/ClientHandle.cpp
@@ -699,7 +699,7 @@ void cClientHandle::HandlePing(void)
 	AString Reply;
 	const cServer & Server = *cRoot::Get()->GetServer();
 
-	Printf(Reply, "%s%s" SIZE_T_FMT "%s" SIZE_T_FMT,
+	Printf(Reply, "%s%s%zu%s%zu",
 		Server.GetDescription().c_str(),
 		cChatColor::Delimiter,
 		Server.GetNumPlayers(),
diff --git a/src/CommandOutput.cpp b/src/CommandOutput.cpp
index 663838fac..a558facdb 100644
--- a/src/CommandOutput.cpp
+++ b/src/CommandOutput.cpp
@@ -13,13 +13,9 @@
 ////////////////////////////////////////////////////////////////////////////////
 // cCommandOutputCallback:
 
-void cCommandOutputCallback::Out(const char * a_Fmt, ...)
+void cCommandOutputCallback::Out(const char * a_Fmt, fmt::ArgList args)
 {
-	AString Output;
-	va_list args;
-	va_start(args, a_Fmt);
-	AppendVPrintf(Output, a_Fmt, args);
-	va_end(args);
+	AString Output = Printf(a_Fmt, args);
 	Output.append("\n");
 	Out(Output);
 }
diff --git a/src/CommandOutput.h b/src/CommandOutput.h
index c9aa053c0..8ae50d221 100644
--- a/src/CommandOutput.h
+++ b/src/CommandOutput.h
@@ -16,7 +16,8 @@ public:
 	virtual ~cCommandOutputCallback() {}  // Force a virtual destructor in subclasses
 
 	/** Syntax sugar function, calls Out() with Printf()-ed parameters; appends a newline" */
-	void Out(const char * a_Fmt, ...) FORMATSTRING(2, 3);
+	void Out(const char * a_Fmt, fmt::ArgList);
+	FMT_VARIADIC(void, Out, const char *)
 
 	/** Called when the command wants to output anything; may be called multiple times */
 	virtual void Out(const AString & a_Text) = 0;
diff --git a/src/CraftingRecipes.cpp b/src/CraftingRecipes.cpp
index 3aa9074e2..f59f49c11 100644
--- a/src/CraftingRecipes.cpp
+++ b/src/CraftingRecipes.cpp
@@ -352,7 +352,7 @@ void cCraftingRecipes::LoadRecipes(void)
 		}
 		AddRecipeLine(LineNum, Recipe);
 	}  // for itr - Split[]
-	LOG("Loaded " SIZE_T_FMT " crafting recipes", m_Recipes.size());
+	LOG("Loaded %zu crafting recipes", m_Recipes.size());
 }
 
 
@@ -380,7 +380,7 @@ void cCraftingRecipes::AddRecipeLine(int a_LineNum, const AString & a_RecipeLine
 	AStringVector Sides = StringSplit(RecipeLine, "=");
 	if (Sides.size() != 2)
 	{
-		LOGWARNING("crafting.txt: line %d: A single '=' was expected, got " SIZE_T_FMT, a_LineNum, Sides.size() - 1);
+		LOGWARNING("crafting.txt: line %d: A single '=' was expected, got %zu", a_LineNum, Sides.size() - 1);
 		LOGINFO("Offending line: \"%s\"", a_RecipeLine.c_str());
 		return;
 	}
diff --git a/src/Entities/CMakeLists.txt b/src/Entities/CMakeLists.txt
index 780243d8c..9bf49ebca 100644
--- a/src/Entities/CMakeLists.txt
+++ b/src/Entities/CMakeLists.txt
@@ -62,5 +62,5 @@ SET (HDRS
 
 if(NOT MSVC)
 	add_library(Entities ${SRCS} ${HDRS})
-	target_link_libraries(Entities WorldStorage)
+	target_link_libraries(Entities fmt::fmt WorldStorage)
 endif()
diff --git a/src/FurnaceRecipe.cpp b/src/FurnaceRecipe.cpp
index 4e7f13e6a..a2199cd33 100644
--- a/src/FurnaceRecipe.cpp
+++ b/src/FurnaceRecipe.cpp
@@ -106,7 +106,7 @@ void cFurnaceRecipe::ReloadRecipes(void)
 		}  // switch (ParsingLine[0])
 	}  // while (getline(ParsingLine))
 
-	LOG("Loaded " SIZE_T_FMT " furnace recipes and " SIZE_T_FMT " fuels", m_pState->Recipes.size(), m_pState->Fuel.size());
+	LOG("Loaded %zu furnace recipes and %zu fuels", m_pState->Recipes.size(), m_pState->Fuel.size());
 }
 
 
@@ -125,7 +125,7 @@ void cFurnaceRecipe::AddFuelFromLine(const AString & a_Line, unsigned int a_Line
 	const AStringVector & Sides = StringSplit(Line, "=");
 	if (Sides.size() != 2)
 	{
-		LOGWARNING("furnace.txt: line %d: A single '=' was expected, got " SIZE_T_FMT, a_LineNum, Sides.size() - 1);
+		LOGWARNING("furnace.txt: line %d: A single '=' was expected, got %zu", a_LineNum, Sides.size() - 1);
 		LOGINFO("Offending line: \"%s\"", a_Line.c_str());
 		return;
 	}
@@ -167,7 +167,7 @@ void cFurnaceRecipe::AddRecipeFromLine(const AString & a_Line, unsigned int a_Li
 	const AStringVector & Sides = StringSplit(Line, "=");
 	if (Sides.size() != 2)
 	{
-		LOGWARNING("furnace.txt: line %d: A single '=' was expected, got " SIZE_T_FMT, a_LineNum, Sides.size() - 1);
+		LOGWARNING("furnace.txt: line %d: A single '=' was expected, got %zu", a_LineNum, Sides.size() - 1);
 		LOGINFO("Offending line: \"%s\"", a_Line.c_str());
 		return;
 	}
diff --git a/src/Generating/CMakeLists.txt b/src/Generating/CMakeLists.txt
index 02f94729f..c7980a096 100644
--- a/src/Generating/CMakeLists.txt
+++ b/src/Generating/CMakeLists.txt
@@ -76,5 +76,5 @@ endif()
 
 if(NOT MSVC)
 	add_library(Generating ${SRCS} ${HDRS})
-	target_link_libraries(Generating OSSupport Blocks Bindings)
+	target_link_libraries(Generating fmt::fmt OSSupport Blocks Bindings)
 endif()
diff --git a/src/Generating/ChunkGenerator.cpp b/src/Generating/ChunkGenerator.cpp
index d66838f9e..e0fee5bd0 100644
--- a/src/Generating/ChunkGenerator.cpp
+++ b/src/Generating/ChunkGenerator.cpp
@@ -118,7 +118,7 @@ void cChunkGenerator::QueueGenerateChunk(int a_ChunkX, int a_ChunkZ, bool a_Forc
 		// Add to queue, issue a warning if too many:
 		if (m_Queue.size() >= QUEUE_WARNING_LIMIT)
 		{
-			LOGWARN("WARNING: Adding chunk [%i, %i] to generation queue; Queue is too big! (" SIZE_T_FMT ")", a_ChunkX, a_ChunkZ, m_Queue.size());
+			LOGWARN("WARNING: Adding chunk [%i, %i] to generation queue; Queue is too big! (%zu)", a_ChunkX, a_ChunkZ, m_Queue.size());
 		}
 		m_Queue.push_back(cQueueItem{a_ChunkX, a_ChunkZ, a_ForceGenerate, a_Callback});
 	}
diff --git a/src/Generating/PieceGeneratorBFSTree.cpp b/src/Generating/PieceGeneratorBFSTree.cpp
index 0078d53c9..1d0be3482 100644
--- a/src/Generating/PieceGeneratorBFSTree.cpp
+++ b/src/Generating/PieceGeneratorBFSTree.cpp
@@ -294,14 +294,14 @@ void cPieceGeneratorBFSTree::PlacePieces(int a_BlockX, int a_BlockZ, int a_MaxDe
 // DEBUG:
 void cPieceGeneratorBFSTree::DebugConnectorPool(const cPieceGeneratorBFSTree::cFreeConnectors & a_ConnectorPool, size_t a_NumProcessed)
 {
-	printf("  Connector pool: " SIZE_T_FMT " items\n", a_ConnectorPool.size() - a_NumProcessed);
+	fmt::print("  Connector pool: {0} items\n", a_ConnectorPool.size() - a_NumProcessed);
 	size_t idx = 0;
 
 	typedef cPieceGeneratorBFSTree::cFreeConnectors::difference_type difType;
 
 	for (auto itr = a_ConnectorPool.cbegin() + static_cast<difType>(a_NumProcessed), end = a_ConnectorPool.cend(); itr != end; ++itr, ++idx)
 	{
-		printf("    " SIZE_T_FMT ": {%d, %d, %d}, type %d, direction %s, depth %d\n",
+		fmt::print("    {0}: {{{1}, {2}, {3}}}, type {4}, direction {5}, depth {6}\n",
 			idx,
 			itr->m_Connector.m_Pos.x, itr->m_Connector.m_Pos.y, itr->m_Connector.m_Pos.z,
 			itr->m_Connector.m_Type,
diff --git a/src/Generating/PieceStructuresGen.cpp b/src/Generating/PieceStructuresGen.cpp
index c8630fa13..2dae8c295 100644
--- a/src/Generating/PieceStructuresGen.cpp
+++ b/src/Generating/PieceStructuresGen.cpp
@@ -138,7 +138,7 @@ bool cPieceStructuresGen::Initialize(const AString & a_Prefabs, int a_SeaLevel,
 	auto structures = StringSplitAndTrim(a_Prefabs, "|");
 	for (const auto & s: structures)
 	{
-		auto fileName = Printf("Prefabs%cPieceStructures%c%s.cubeset", cFile::PathSeparator, cFile::PathSeparator, s.c_str());
+		auto fileName = Printf("Prefabs%cPieceStructures%c%s.cubeset", cFile::PathSeparator(), cFile::PathSeparator(), s.c_str());
 		if (!cFile::IsFile(fileName))
 		{
 			fileName.append(".gz");
diff --git a/src/Globals.h b/src/Globals.h
index 78c0539fb..e48c6dbfe 100644
--- a/src/Globals.h
+++ b/src/Globals.h
@@ -38,13 +38,6 @@
 
 	#define OBSOLETE __declspec(deprecated)
 
-	#define FORMATSTRING(formatIndex, va_argsIndex)
-
-	// MSVC has its own custom version of zu format
-	#define SIZE_T_FMT "%Iu"
-	#define SIZE_T_FMT_PRECISION(x) "%" #x "Iu"
-	#define SIZE_T_FMT_HEX "%Ix"
-
 	#define NORETURN __declspec(noreturn)
 	#if (_MSC_VER < 1900)  // noexcept support was added in VS 2015
 		#define NOEXCEPT  throw()
@@ -87,27 +80,6 @@
 
 	#define OBSOLETE __attribute__((deprecated))
 
-	#define FORMATSTRING(formatIndex, va_argsIndex) __attribute__((format (printf, formatIndex, va_argsIndex)))
-
-	#if defined(_WIN32)
-		// We're compiling on MinGW, which uses an old MSVCRT library that has no support for size_t printfing.
-		// We need direct size formats:
-		#if defined(_WIN64)
-			#define SIZE_T_FMT "%I64u"
-			#define SIZE_T_FMT_PRECISION(x) "%" #x "I64u"
-			#define SIZE_T_FMT_HEX "%I64x"
-		#else
-			#define SIZE_T_FMT "%u"
-			#define SIZE_T_FMT_PRECISION(x) "%" #x "u"
-			#define SIZE_T_FMT_HEX "%x"
-		#endif
-	#else
-		// We're compiling on Linux, so we can use libc's size_t printf format:
-		#define SIZE_T_FMT "%zu"
-		#define SIZE_T_FMT_PRECISION(x) "%" #x "zu"
-		#define SIZE_T_FMT_HEX "%zx"
-	#endif
-
 	#define NORETURN __attribute((__noreturn__))
 	#define NOEXCEPT  noexcept
 	#define CAN_THROW noexcept(false)
@@ -263,6 +235,7 @@ template class SizeChecker<UInt8,  1>;
 
 
 // Common headers (part 1, without macros):
+#include "fmt/format.h"
 #include "StringUtils.h"
 #include "OSSupport/CriticalSection.h"
 #include "OSSupport/Event.h"
@@ -271,73 +244,39 @@ template class SizeChecker<UInt8,  1>;
 
 #ifndef TEST_GLOBALS
 
-	// These functions are defined in Logger.cpp, but are declared here to avoid including all of logger.h
-	extern void LOG       (const char * a_Format, ...) FORMATSTRING(1, 2);
-	extern void LOGINFO   (const char * a_Format, ...) FORMATSTRING(1, 2);
-	extern void LOGWARNING(const char * a_Format, ...) FORMATSTRING(1, 2);
-	extern void LOGERROR  (const char * a_Format, ...) FORMATSTRING(1, 2);
-
-	// In debug builds, translate LOGD to LOG, otherwise leave it out altogether:
-	#ifdef _DEBUG
-		#define LOGD LOG
-	#else
-		#define LOGD(...)
-	#endif  // _DEBUG
-
-	#define LOGWARN LOGWARNING
+	#include "LoggerSimple.h"
 
 #else
-	// Logging functions
-	void inline LOGERROR(const char * a_Format, ...) FORMATSTRING(1, 2);
+	#include "fmt/printf.h"
 
-	void inline LOGERROR(const char * a_Format, ...)
-	{
-		va_list argList;
-		va_start(argList, a_Format);
-		vprintf(a_Format, argList);
-		putchar('\n');
-		fflush(stdout);
-		va_end(argList);
-	}
-
-	void inline LOGWARNING(const char * a_Format, ...) FORMATSTRING(1, 2);
-
-	void inline LOGWARNING(const char * a_Format, ...)
-	{
-		va_list argList;
-		va_start(argList, a_Format);
-		vprintf(a_Format, argList);
-		putchar('\n');
-		fflush(stdout);
-		va_end(argList);
-	}
-
-	void inline LOGD(const char * a_Format, ...) FORMATSTRING(1, 2);
-
-	void inline LOGD(const char * a_Format, ...)
+	// Logging functions
+	template <typename ... Args>
+	void LOG(const char * a_Format, const Args & ... a_Args)
 	{
-		va_list argList;
-		va_start(argList, a_Format);
-		vprintf(a_Format, argList);
+		fmt::printf(a_Format, a_Args...);
 		putchar('\n');
 		fflush(stdout);
-		va_end(argList);
 	}
 
-	void inline LOG(const char * a_Format, ...) FORMATSTRING(1, 2);
+	#define LOGERROR   LOG
+	#define LOGWARNING LOG
+	#define LOGD       LOG
+	#define LOGINFO    LOG
+	#define LOGWARN    LOG
 
-	void inline LOG(const char * a_Format, ...)
+	template <typename ... Args>
+	void FLOG(const char * a_Format, const Args & ... a_Args)
 	{
-		va_list argList;
-		va_start(argList, a_Format);
-		vprintf(a_Format, argList);
+		fmt::print(a_Format, a_Args...);
 		putchar('\n');
 		fflush(stdout);
-		va_end(argList);
 	}
 
-	#define LOGINFO LOG
-	#define LOGWARN LOGWARNING
+	#define FLOGERROR   FLOG
+	#define FLOGWARNING FLOG
+	#define FLOGD       FLOG
+	#define FLOGINFO    FLOG
+	#define FLOGWARN    FLOG
 
 #endif
 
diff --git a/src/HTTP/CMakeLists.txt b/src/HTTP/CMakeLists.txt
index f15c35764..0f12e4e7c 100644
--- a/src/HTTP/CMakeLists.txt
+++ b/src/HTTP/CMakeLists.txt
@@ -34,4 +34,5 @@ SET (HDRS
 
 if(NOT MSVC)
 	add_library(HTTPServer ${SRCS} ${HDRS})
+	target_link_libraries(HTTPServer fmt::fmt)
 endif()
diff --git a/src/HTTP/HTTPServerConnection.cpp b/src/HTTP/HTTPServerConnection.cpp
index d949fcf4d..494aa42c6 100644
--- a/src/HTTP/HTTPServerConnection.cpp
+++ b/src/HTTP/HTTPServerConnection.cpp
@@ -74,7 +74,7 @@ void cHTTPServerConnection::Send(const void * a_Data, size_t a_Size)
 {
 	ASSERT(m_CurrentRequest != nullptr);
 	// We're sending in Chunked transfer encoding
-	SendData(Printf(SIZE_T_FMT_HEX "\r\n", a_Size));
+	SendData(fmt::format("{0:x}\r\n", a_Size));
 	SendData(a_Data, a_Size);
 	SendData("\r\n");
 }
diff --git a/src/Item.cpp b/src/Item.cpp
index 9b17f1c37..b3c906037 100644
--- a/src/Item.cpp
+++ b/src/Item.cpp
@@ -628,7 +628,7 @@ cItem * cItems::Get(int a_Idx)
 {
 	if ((a_Idx < 0) || (a_Idx >= static_cast<int>(size())))
 	{
-		LOGWARNING("cItems: Attempt to get an out-of-bounds item at index %d; there are currently " SIZE_T_FMT " items. Returning a nil.", a_Idx, size());
+		LOGWARNING("cItems: Attempt to get an out-of-bounds item at index %d; there are currently %zu items. Returning a nil.", a_Idx, size());
 		return nullptr;
 	}
 	return &at(static_cast<size_t>(a_Idx));
@@ -642,7 +642,7 @@ void cItems::Set(int a_Idx, const cItem & a_Item)
 {
 	if ((a_Idx < 0) || (a_Idx >= static_cast<int>(size())))
 	{
-		LOGWARNING("cItems: Attempt to set an item at an out-of-bounds index %d; there are currently " SIZE_T_FMT " items. Not setting.", a_Idx, size());
+		LOGWARNING("cItems: Attempt to set an item at an out-of-bounds index %d; there are currently %zu items. Not setting.", a_Idx, size());
 		return;
 	}
 	at(static_cast<size_t>(a_Idx)) = a_Item;
@@ -656,7 +656,7 @@ void cItems::Delete(int a_Idx)
 {
 	if ((a_Idx < 0) || (a_Idx >= static_cast<int>(size())))
 	{
-		LOGWARNING("cItems: Attempt to delete an item at an out-of-bounds index %d; there are currently " SIZE_T_FMT " items. Ignoring.", a_Idx, size());
+		LOGWARNING("cItems: Attempt to delete an item at an out-of-bounds index %d; there are currently %zu items. Ignoring.", a_Idx, size());
 		return;
 	}
 	erase(begin() + a_Idx);
@@ -670,7 +670,7 @@ void cItems::Set(int a_Idx, short a_ItemType, char a_ItemCount, short a_ItemDama
 {
 	if ((a_Idx < 0) || (a_Idx >= static_cast<int>(size())))
 	{
-		LOGWARNING("cItems: Attempt to set an item at an out-of-bounds index %d; there are currently " SIZE_T_FMT " items. Not setting.", a_Idx, size());
+		LOGWARNING("cItems: Attempt to set an item at an out-of-bounds index %d; there are currently %zu items. Not setting.", a_Idx, size());
 		return;
 	}
 	at(static_cast<size_t>(a_Idx)) = cItem(a_ItemType, a_ItemCount, a_ItemDamage);
diff --git a/src/Items/CMakeLists.txt b/src/Items/CMakeLists.txt
index ba0e4ca9f..af09b32ae 100644
--- a/src/Items/CMakeLists.txt
+++ b/src/Items/CMakeLists.txt
@@ -60,4 +60,5 @@ SET (HDRS
 
 if(NOT MSVC)
 	add_library(Items ${SRCS} ${HDRS})
+	target_link_libraries(Items fmt::fmt)
 endif()
diff --git a/src/Logger.cpp b/src/Logger.cpp
index 60f5a88d2..f0080e73c 100644
--- a/src/Logger.cpp
+++ b/src/Logger.cpp
@@ -63,11 +63,18 @@ void cLogger::LogSimple(AString a_Message, eLogLevel a_LogLevel)
 
 
 
-void cLogger::Log(const char * a_Format, eLogLevel a_LogLevel, va_list a_ArgList)
+void cLogger::LogPrintf(const char * a_Format, eLogLevel a_LogLevel, fmt::ArgList a_ArgList)
 {
-	AString Message;
-	AppendVPrintf(Message, a_Format, a_ArgList);
-	LogSimple(Message, a_LogLevel);
+	LogSimple(Printf(a_Format, a_ArgList), a_LogLevel);
+}
+
+
+
+
+
+void cLogger::LogFormat(const char * a_Format, eLogLevel a_LogLevel, fmt::ArgList a_ArgList)
+{
+	LogSimple(fmt::format(a_Format, a_ArgList), a_LogLevel);
 }
 
 
@@ -110,48 +117,72 @@ void cLogger::DetachListener(cListener * a_Listener)
 ////////////////////////////////////////////////////////////////////////////////
 // Global functions
 
-void LOG(const char * a_Format, ...)
+void FLOG(const char * a_Format, fmt::ArgList a_ArgList)
+{
+	cLogger::GetInstance().LogFormat(a_Format, cLogger::llRegular, a_ArgList);
+}
+
+
+
+
+
+void FLOGINFO(const char * a_Format, fmt::ArgList a_ArgList)
+{
+	cLogger::GetInstance().LogFormat( a_Format, cLogger::llInfo, a_ArgList);
+}
+
+
+
+
+
+void FLOGWARNING(const char * a_Format, fmt::ArgList a_ArgList)
+{
+	cLogger::GetInstance().LogFormat( a_Format, cLogger::llWarning, a_ArgList);
+}
+
+
+
+
+
+void FLOGERROR(const char * a_Format, fmt::ArgList a_ArgList)
+{
+	cLogger::GetInstance().LogFormat( a_Format, cLogger::llError, a_ArgList);
+}
+
+
+
+
+
+void LOG(const char * a_Format, fmt::ArgList a_ArgList)
 {
-	va_list argList;
-	va_start(argList, a_Format);
-	cLogger::GetInstance().Log(a_Format, cLogger::llRegular, argList);
-	va_end(argList);
+	cLogger::GetInstance().LogPrintf(a_Format, cLogger::llRegular, a_ArgList);
 }
 
 
 
 
 
-void LOGINFO(const char * a_Format, ...)
+void LOGINFO(const char * a_Format, fmt::ArgList a_ArgList)
 {
-	va_list argList;
-	va_start(argList, a_Format);
-	cLogger::GetInstance().Log( a_Format, cLogger::llInfo, argList);
-	va_end(argList);
+	cLogger::GetInstance().LogPrintf( a_Format, cLogger::llInfo, a_ArgList);
 }
 
 
 
 
 
-void LOGWARNING(const char * a_Format, ...)
+void LOGWARNING(const char * a_Format, fmt::ArgList a_ArgList)
 {
-	va_list argList;
-	va_start(argList, a_Format);
-	cLogger::GetInstance().Log( a_Format, cLogger::llWarning, argList);
-	va_end(argList);
+	cLogger::GetInstance().LogPrintf( a_Format, cLogger::llWarning, a_ArgList);
 }
 
 
 
 
 
-void LOGERROR(const char * a_Format, ...)
+void LOGERROR(const char * a_Format, fmt::ArgList a_ArgList)
 {
-	va_list argList;
-	va_start(argList, a_Format);
-	cLogger::GetInstance().Log( a_Format, cLogger::llError, argList);
-	va_end(argList);
+	cLogger::GetInstance().LogPrintf( a_Format, cLogger::llError, a_ArgList);
 }
 
 
diff --git a/src/Logger.h b/src/Logger.h
index b4bf97cd6..14c02d825 100644
--- a/src/Logger.h
+++ b/src/Logger.h
@@ -58,7 +58,13 @@ public:
 		cAttachment(cListener * a_listener) : m_listener(a_listener) {}
 	};
 
-	void Log  (const char * a_Format, eLogLevel a_LogLevel, va_list a_ArgList) FORMATSTRING(2, 0);
+	/** Log a message formatted with a printf style formatting string. */
+	void LogPrintf(const char * a_Format, eLogLevel a_LogLevel, fmt::ArgList a_ArgList);
+	FMT_VARIADIC(void, LogPrintf, const char *, eLogLevel)
+
+	/** Log a message formatted with a python style formatting string. */
+	void LogFormat(const char * a_Format, eLogLevel a_LogLevel, fmt::ArgList a_ArgList);
+	FMT_VARIADIC(void, LogFormat, const char *, eLogLevel)
 
 	/** Logs the simple text message at the specified log level. */
 	void LogSimple(AString a_Message, eLogLevel a_LogLevel = llRegular);
@@ -79,12 +85,3 @@ private:
 
 
 
-
-// These declarations are duplicated in globals.h
-extern void LOG       (const char * a_Format, ...) FORMATSTRING(1, 2);
-extern void LOGINFO   (const char * a_Format, ...) FORMATSTRING(1, 2);
-extern void LOGWARNING(const char * a_Format, ...) FORMATSTRING(1, 2);
-extern void LOGERROR  (const char * a_Format, ...) FORMATSTRING(1, 2);
-
-
-
diff --git a/src/LoggerSimple.h b/src/LoggerSimple.h
new file mode 100644
index 000000000..5c0487607
--- /dev/null
+++ b/src/LoggerSimple.h
@@ -0,0 +1,51 @@
+
+// Logging free functions defined in Logger.cpp
+#pragma once
+
+// python style format specified logging
+
+extern void FLOG(const char * a_Format, fmt::ArgList a_ArgList);
+FMT_VARIADIC(void, FLOG, const char *)
+
+extern void FLOGINFO(const char * a_Format, fmt::ArgList a_ArgList);
+FMT_VARIADIC(void, FLOGINFO, const char *)
+
+extern void FLOGWARNING(const char * a_Format, fmt::ArgList a_ArgList);
+FMT_VARIADIC(void, FLOGWARNING, const char *)
+
+extern void FLOGERROR(const char * a_Format, fmt::ArgList a_ArgList);
+FMT_VARIADIC(void, FLOGERROR, const char *)
+
+// printf style format specified logging (DEPRECATED)
+
+extern void LOG(const char * a_Format, fmt::ArgList a_ArgList);
+FMT_VARIADIC(void, LOG, const char *)
+
+extern void LOGINFO(const char * a_Format, fmt::ArgList a_ArgList);
+FMT_VARIADIC(void, LOGINFO, const char *)
+
+extern void LOGWARNING(const char * a_Format, fmt::ArgList a_ArgList);
+FMT_VARIADIC(void, LOGWARNING, const char *)
+
+extern void LOGERROR(const char * a_Format, fmt::ArgList a_ArgList);
+FMT_VARIADIC(void, LOGERROR, const char *)
+
+
+// Macro variants
+
+// In debug builds, translate LOGD to LOG, otherwise leave it out altogether:
+#ifdef _DEBUG
+	#define LOGD LOG
+#else
+	#define LOGD(...)
+#endif  // _DEBUG
+
+#define LOGWARN LOGWARNING
+
+#ifdef _DEBUG
+	#define FLOGD FLOG
+#else
+	#define FLOGD(...)
+#endif  // _DEBUG
+
+#define FLOGWARN FLOGWARNING
diff --git a/src/Mobs/CMakeLists.txt b/src/Mobs/CMakeLists.txt
index 08df07d71..fedff213b 100644
--- a/src/Mobs/CMakeLists.txt
+++ b/src/Mobs/CMakeLists.txt
@@ -83,4 +83,5 @@ SET (HDRS
 
 if(NOT MSVC)
 	add_library(Mobs ${SRCS} ${HDRS})
+	target_link_libraries(Mobs fmt::fmt)
 endif()
diff --git a/src/Noise/CMakeLists.txt b/src/Noise/CMakeLists.txt
index 167ae7588..3e3462900 100644
--- a/src/Noise/CMakeLists.txt
+++ b/src/Noise/CMakeLists.txt
@@ -15,5 +15,5 @@ SET (HDRS
 
 if(NOT MSVC)
 	add_library(Noise ${SRCS} ${HDRS})
-	target_link_libraries(Noise OSSupport)
+	target_link_libraries(Noise fmt::fmt OSSupport)
 endif()
diff --git a/src/Noise/Noise.cpp b/src/Noise/Noise.cpp
index cc63a34a9..7249adda5 100644
--- a/src/Noise/Noise.cpp
+++ b/src/Noise/Noise.cpp
@@ -119,7 +119,7 @@ void Debug3DNoise(const NOISE_DATATYPE * a_Noise, size_t a_SizeX, size_t a_SizeY
 
 	// Save in XY cuts:
 	cFile f1;
-	if (f1.Open(Printf("%s_XY (" SIZE_T_FMT ").grab", a_FileNameBase.c_str(), a_SizeX), cFile::fmWrite))
+	if (f1.Open(Printf("%s_XY (%zu).grab", a_FileNameBase.c_str(), a_SizeX), cFile::fmWrite))
 	{
 		for (size_t z = 0; z < a_SizeZ; z++)
 		{
@@ -140,7 +140,7 @@ void Debug3DNoise(const NOISE_DATATYPE * a_Noise, size_t a_SizeX, size_t a_SizeY
 	}  // if (XY file open)
 
 	cFile f2;
-	if (f2.Open(Printf("%s_XZ (" SIZE_T_FMT ").grab", a_FileNameBase.c_str(), a_SizeX), cFile::fmWrite))
+	if (f2.Open(Printf("%s_XZ (%zu).grab", a_FileNameBase.c_str(), a_SizeX), cFile::fmWrite))
 	{
 		for (size_t y = 0; y < a_SizeY; y++)
 		{
@@ -171,7 +171,7 @@ void Debug2DNoise(const NOISE_DATATYPE * a_Noise, size_t a_SizeX, size_t a_SizeY
 	ASSERT(a_SizeX <= BUF_SIZE);  // Just stretch it, if needed
 
 	cFile f1;
-	if (f1.Open(Printf("%s (" SIZE_T_FMT ").grab", a_FileNameBase.c_str(), a_SizeX), cFile::fmWrite))
+	if (f1.Open(Printf("%s (%zu).grab", a_FileNameBase.c_str(), a_SizeX), cFile::fmWrite))
 	{
 		for (size_t y = 0; y < a_SizeY; y++)
 		{
diff --git a/src/OSSupport/CMakeLists.txt b/src/OSSupport/CMakeLists.txt
index e6fb37987..55d2dd87a 100644
--- a/src/OSSupport/CMakeLists.txt
+++ b/src/OSSupport/CMakeLists.txt
@@ -48,4 +48,5 @@ endif()
 
 if(NOT MSVC)
 	add_library(OSSupport ${SRCS} ${HDRS})
+	target_link_libraries(OSSupport fmt::fmt)
 endif()
diff --git a/src/OSSupport/File.cpp b/src/OSSupport/File.cpp
index 166de8f46..8b91cc2a4 100644
--- a/src/OSSupport/File.cpp
+++ b/src/OSSupport/File.cpp
@@ -690,13 +690,9 @@ AString cFile::GetExecutableExt(void)
 
 
 
-int cFile::Printf(const char * a_Fmt, ...)
+int cFile::Printf(const char * a_Fmt, fmt::ArgList a_ArgList)
 {
-	AString buf;
-	va_list args;
-	va_start(args, a_Fmt);
-	AppendVPrintf(buf, a_Fmt, args);
-	va_end(args);
+	AString buf = ::Printf(a_Fmt, a_ArgList);
 	return Write(buf.c_str(), buf.length());
 }
 
diff --git a/src/OSSupport/File.h b/src/OSSupport/File.h
index 28485d9f8..59bb61974 100644
--- a/src/OSSupport/File.h
+++ b/src/OSSupport/File.h
@@ -39,12 +39,14 @@ class cFile
 public:
 
 	// tolua_end
-
-	#ifdef _WIN32
-	static const char PathSeparator = '\\';
-	#else
-	static const char PathSeparator = '/';
-	#endif
+	inline static char PathSeparator()
+	{
+		#ifdef _WIN32
+			return '\\';
+		#else
+			return '/';
+		#endif
+	}
 
 	/** The mode in which to open the file */
 	enum eMode
@@ -161,7 +163,8 @@ public:
 	/** Returns the list of all items in the specified folder (files, folders, nix pipes, whatever's there). */
 	static AStringVector GetFolderContents(const AString & a_Folder);  // Exported in ManualBindings.cpp
 
-	int Printf(const char * a_Fmt, ...) FORMATSTRING(2, 3);
+	int Printf(const char * a_Fmt, fmt::ArgList);
+	FMT_VARIADIC(int, Printf, const char *)
 
 	/** Flushes all the bufferef output into the file (only when writing) */
 	void Flush(void);
diff --git a/src/Protocol/CMakeLists.txt b/src/Protocol/CMakeLists.txt
index ff1a98e6b..5cc7654ba 100644
--- a/src/Protocol/CMakeLists.txt
+++ b/src/Protocol/CMakeLists.txt
@@ -34,4 +34,5 @@ SET (HDRS
 
 if (NOT MSVC)
 	add_library(Protocol ${SRCS} ${HDRS})
+	target_link_libraries(Protocol fmt::fmt)
 endif()
diff --git a/src/Protocol/ForgeHandshake.cpp b/src/Protocol/ForgeHandshake.cpp
index 48b89baf4..b6f7a7c94 100644
--- a/src/Protocol/ForgeHandshake.cpp
+++ b/src/Protocol/ForgeHandshake.cpp
@@ -146,7 +146,7 @@ AStringMap cForgeHandshake::ParseModList(const char * a_Data, size_t a_Size)
 
 	if (a_Size < 4)
 	{
-		SetError(Printf("ParseModList invalid packet, missing length (size = " SIZE_T_FMT ")", a_Size));
+		SetError(Printf("ParseModList invalid packet, missing length (size = %zu)", a_Size));
 		return Mods;
 	}
 
@@ -194,7 +194,7 @@ void cForgeHandshake::HandleClientHello(cClientHandle * a_Client, const char * a
 	}
 	else
 	{
-		SetError(Printf("Received unexpected length of ClientHello: " SIZE_T_FMT, a_Size));
+		SetError(Printf("Received unexpected length of ClientHello: %zu", a_Size));
 	}
 }
 
@@ -212,7 +212,7 @@ void cForgeHandshake::HandleModList(cClientHandle * a_Client, const char * a_Dat
 		AppendPrintf(ClientModsString, "%s@%s, ", item.first.c_str(), item.second.c_str());
 	}
 
-	LOG("Client connected with " SIZE_T_FMT " mods: %s", ClientMods.size(), ClientModsString.c_str());
+	LOG("Client connected with %zu mods: %s", ClientMods.size(), ClientModsString.c_str());
 
 	m_Client->m_ForgeMods = ClientMods;
 
@@ -252,7 +252,7 @@ void cForgeHandshake::HandleHandshakeAck(cClientHandle * a_Client, const char *
 {
 	if (a_Size != 2)
 	{
-		SetError(Printf("Unexpected HandshakeAck packet length: " SIZE_T_FMT "", a_Size));
+		SetError(Printf("Unexpected HandshakeAck packet length: %zu", a_Size));
 		return;
 	}
 
@@ -331,7 +331,7 @@ void cForgeHandshake::DataReceived(cClientHandle * a_Client, const char * a_Data
 {
 	if (!m_IsForgeClient)
 	{
-		SetError(Printf("Received unexpected Forge data from non-Forge client (" SIZE_T_FMT " bytes)", a_Size));
+		SetError(Printf("Received unexpected Forge data from non-Forge client (%zu bytes)", a_Size));
 		return;
 	}
 	if (m_Errored)
@@ -342,7 +342,7 @@ void cForgeHandshake::DataReceived(cClientHandle * a_Client, const char * a_Data
 
 	if (a_Size <= 1)
 	{
-		SetError(Printf("Received unexpectedly short Forge data (" SIZE_T_FMT " bytes)", a_Size));
+		SetError(Printf("Received unexpectedly short Forge data (%zu bytes)", a_Size));
 		return;
 	}
 
diff --git a/src/Protocol/Protocol_1_8.cpp b/src/Protocol/Protocol_1_8.cpp
index ec5a9440b..4568ad8cb 100644
--- a/src/Protocol/Protocol_1_8.cpp
+++ b/src/Protocol/Protocol_1_8.cpp
@@ -1867,7 +1867,7 @@ void cProtocol_1_8_0::AddReceivedData(const char * a_Data, size_t a_Size)
 			ASSERT(m_ReceivedData.GetReadableSpace() == OldReadableSpace);
 			AString Hex;
 			CreateHexDump(Hex, AllData.data(), AllData.size(), 16);
-			m_CommLogFile.Printf("Incoming data, " SIZE_T_FMT " (0x" SIZE_T_FMT_HEX ") unparsed bytes already present in buffer:\n%s\n",
+			m_CommLogFile.Printf("Incoming data, %zu (0x%zx) unparsed bytes already present in buffer:\n%s\n",
 				AllData.size(), AllData.size(), Hex.c_str()
 			);
 		}
@@ -2008,14 +2008,14 @@ void cProtocol_1_8_0::AddReceivedData(const char * a_Data, size_t a_Size)
 		if (bb.GetReadableSpace() != 1)
 		{
 			// Read more or less than packet length, report as error
-			LOGWARNING("Protocol 1.8: Wrong number of bytes read for packet 0x%x, state %d. Read " SIZE_T_FMT " bytes, packet contained %u bytes",
+			LOGWARNING("Protocol 1.8: Wrong number of bytes read for packet 0x%x, state %d. Read %zu bytes, packet contained %u bytes",
 				PacketType, m_State, bb.GetUsedSpace() - bb.GetReadableSpace(), PacketLen
 			);
 
 			// Put a message in the comm log:
 			if (g_ShouldLogCommIn && m_CommLogFile.IsOpen())
 			{
-				m_CommLogFile.Printf("^^^^^^ Wrong number of bytes read for this packet (exp %d left, got " SIZE_T_FMT " left) ^^^^^^\n\n\n",
+				m_CommLogFile.Printf("^^^^^^ Wrong number of bytes read for this packet (exp %d left, got %zu left) ^^^^^^\n\n\n",
 					1, bb.GetReadableSpace()
 				);
 				m_CommLogFile.Flush();
@@ -2037,7 +2037,7 @@ void cProtocol_1_8_0::AddReceivedData(const char * a_Data, size_t a_Size)
 		ASSERT(m_ReceivedData.GetReadableSpace() == OldReadableSpace);
 		AString Hex;
 		CreateHexDump(Hex, AllData.data(), AllData.size(), 16);
-		m_CommLogFile.Printf("There are " SIZE_T_FMT " (0x" SIZE_T_FMT_HEX ") bytes of non-parse-able data left in the buffer:\n%s",
+		m_CommLogFile.Printf("There are %zu (0x%zx) bytes of non-parse-able data left in the buffer:\n%s",
 			m_ReceivedData.GetReadableSpace(), m_ReceivedData.GetReadableSpace(), Hex.c_str()
 		);
 		m_CommLogFile.Flush();
@@ -2893,7 +2893,7 @@ void cProtocol_1_8_0::ParseItemMetadata(cItem & a_Item, const AString & a_Metada
 	{
 		AString HexDump;
 		CreateHexDump(HexDump, a_Metadata.data(), std::max<size_t>(a_Metadata.size(), 1024), 16);
-		LOGWARNING("Cannot parse NBT item metadata: %s at (" SIZE_T_FMT " / " SIZE_T_FMT " bytes)\n%s",
+		LOGWARNING("Cannot parse NBT item metadata: %s at (%zu / %zu bytes)\n%s",
 			NBT.GetErrorCode().message().c_str(), NBT.GetErrorPos(), a_Metadata.size(), HexDump.c_str()
 		);
 		return;
diff --git a/src/Protocol/Protocol_1_9.cpp b/src/Protocol/Protocol_1_9.cpp
index 7b61100d0..2b66cc7fa 100644
--- a/src/Protocol/Protocol_1_9.cpp
+++ b/src/Protocol/Protocol_1_9.cpp
@@ -162,7 +162,7 @@ cProtocol_1_9_0::cProtocol_1_9_0(cClientHandle * a_Client, const AString & a_Ser
 		}
 		else
 		{
-			LOG("Unknown additional data sent in server address (BungeeCord/FML?): " SIZE_T_FMT " parameters", Params.size());
+			LOG("Unknown additional data sent in server address (BungeeCord/FML?): %zu parameters", Params.size());
 			// TODO: support FML + BungeeCord? (what parameters does it send in that case?) https://github.com/SpigotMC/BungeeCord/issues/899
 		}
 	}
@@ -1912,7 +1912,7 @@ void cProtocol_1_9_0::AddReceivedData(const char * a_Data, size_t a_Size)
 			ASSERT(m_ReceivedData.GetReadableSpace() == OldReadableSpace);
 			AString Hex;
 			CreateHexDump(Hex, AllData.data(), AllData.size(), 16);
-			m_CommLogFile.Printf("Incoming data, " SIZE_T_FMT " (0x" SIZE_T_FMT_HEX ") unparsed bytes already present in buffer:\n%s\n",
+			m_CommLogFile.Printf("Incoming data, %zu (0x%zx) unparsed bytes already present in buffer:\n%s\n",
 				AllData.size(), AllData.size(), Hex.c_str()
 			);
 		}
@@ -2053,14 +2053,14 @@ void cProtocol_1_9_0::AddReceivedData(const char * a_Data, size_t a_Size)
 		if (bb.GetReadableSpace() != 1)
 		{
 			// Read more or less than packet length, report as error
-			LOGWARNING("Protocol 1.9: Wrong number of bytes read for packet 0x%x, state %d. Read " SIZE_T_FMT " bytes, packet contained %u bytes",
+			LOGWARNING("Protocol 1.9: Wrong number of bytes read for packet 0x%x, state %d. Read %zu bytes, packet contained %u bytes",
 				PacketType, m_State, bb.GetUsedSpace() - bb.GetReadableSpace(), PacketLen
 			);
 
 			// Put a message in the comm log:
 			if (g_ShouldLogCommIn && m_CommLogFile.IsOpen())
 			{
-				m_CommLogFile.Printf("^^^^^^ Wrong number of bytes read for this packet (exp %d left, got " SIZE_T_FMT " left) ^^^^^^\n\n\n",
+				m_CommLogFile.Printf("^^^^^^ Wrong number of bytes read for this packet (exp %d left, got %zu left) ^^^^^^\n\n\n",
 					1, bb.GetReadableSpace()
 				);
 				m_CommLogFile.Flush();
@@ -2082,7 +2082,7 @@ void cProtocol_1_9_0::AddReceivedData(const char * a_Data, size_t a_Size)
 		ASSERT(m_ReceivedData.GetReadableSpace() == OldReadableSpace);
 		AString Hex;
 		CreateHexDump(Hex, AllData.data(), AllData.size(), 16);
-		m_CommLogFile.Printf("Protocol 1.9: There are " SIZE_T_FMT " (0x" SIZE_T_FMT_HEX ") bytes of non-parse-able data left in the buffer:\n%s",
+		m_CommLogFile.Printf("Protocol 1.9: There are %zu (0x%zx) bytes of non-parse-able data left in the buffer:\n%s",
 			m_ReceivedData.GetReadableSpace(), m_ReceivedData.GetReadableSpace(), Hex.c_str()
 		);
 		m_CommLogFile.Flush();
@@ -3029,7 +3029,7 @@ void cProtocol_1_9_0::ParseItemMetadata(cItem & a_Item, const AString & a_Metada
 	{
 		AString HexDump;
 		CreateHexDump(HexDump, a_Metadata.data(), std::max<size_t>(a_Metadata.size(), 1024), 16);
-		LOGWARNING("Cannot parse NBT item metadata: %s at (" SIZE_T_FMT " / " SIZE_T_FMT " bytes)\n%s",
+		LOGWARNING("Cannot parse NBT item metadata: %s at (%zu / %zu bytes)\n%s",
 			NBT.GetErrorCode().message().c_str(), NBT.GetErrorPos(), a_Metadata.size(), HexDump.c_str()
 		);
 		return;
diff --git a/src/Root.cpp b/src/Root.cpp
index 64ac44514..42ee00604 100644
--- a/src/Root.cpp
+++ b/src/Root.cpp
@@ -1029,11 +1029,11 @@ void cRoot::LogChunkStats(cCommandOutputCallback & a_Output)
 		int Mem = NumValid * static_cast<int>(sizeof(cChunk));
 		a_Output.Out("  Memory used by chunks: %d KiB (%d MiB)", (Mem + 1023) / 1024, (Mem + 1024 * 1024 - 1) / (1024 * 1024));
 		a_Output.Out("  Per-chunk memory size breakdown:");
-		a_Output.Out("    block types:    " SIZE_T_FMT_PRECISION(6)  " bytes (" SIZE_T_FMT_PRECISION(3)  " KiB)", sizeof(cChunkDef::BlockTypes), (sizeof(cChunkDef::BlockTypes) + 1023) / 1024);
-		a_Output.Out("    block metadata: " SIZE_T_FMT_PRECISION(6)  " bytes (" SIZE_T_FMT_PRECISION(3)  " KiB)", sizeof(cChunkDef::BlockNibbles), (sizeof(cChunkDef::BlockNibbles) + 1023) / 1024);
-		a_Output.Out("    block lighting: " SIZE_T_FMT_PRECISION(6)  " bytes (" SIZE_T_FMT_PRECISION(3)  " KiB)", 2 * sizeof(cChunkDef::BlockNibbles), (2 * sizeof(cChunkDef::BlockNibbles) + 1023) / 1024);
-		a_Output.Out("    heightmap:      " SIZE_T_FMT_PRECISION(6)  " bytes (" SIZE_T_FMT_PRECISION(3)  " KiB)", sizeof(cChunkDef::HeightMap), (sizeof(cChunkDef::HeightMap) + 1023) / 1024);
-		a_Output.Out("    biomemap:       " SIZE_T_FMT_PRECISION(6)  " bytes (" SIZE_T_FMT_PRECISION(3)  " KiB)", sizeof(cChunkDef::BiomeMap), (sizeof(cChunkDef::BiomeMap) + 1023) / 1024);
+		a_Output.Out("    block types:    %6zu bytes (%3zu KiB)", sizeof(cChunkDef::BlockTypes), (sizeof(cChunkDef::BlockTypes) + 1023) / 1024);
+		a_Output.Out("    block metadata: %6zu bytes (%3zu KiB)", sizeof(cChunkDef::BlockNibbles), (sizeof(cChunkDef::BlockNibbles) + 1023) / 1024);
+		a_Output.Out("    block lighting: %6zu bytes (%3zu KiB)", 2 * sizeof(cChunkDef::BlockNibbles), (2 * sizeof(cChunkDef::BlockNibbles) + 1023) / 1024);
+		a_Output.Out("    heightmap:      %6zu bytes (%3zu KiB)", sizeof(cChunkDef::HeightMap), (sizeof(cChunkDef::HeightMap) + 1023) / 1024);
+		a_Output.Out("    biomemap:       %6zu bytes (%3zu KiB)", sizeof(cChunkDef::BiomeMap), (sizeof(cChunkDef::BiomeMap) + 1023) / 1024);
 		SumNumValid += NumValid;
 		SumNumDirty += NumDirty;
 		SumNumInLighting += NumInLighting;
diff --git a/src/Simulator/CMakeLists.txt b/src/Simulator/CMakeLists.txt
index 5a67dd026..ab17eebe3 100644
--- a/src/Simulator/CMakeLists.txt
+++ b/src/Simulator/CMakeLists.txt
@@ -31,4 +31,5 @@ SET (HDRS
 
 if(NOT MSVC)
 	add_library(Simulator ${SRCS} ${HDRS})
+	target_link_libraries(Simulator fmt::fmt)
 endif()
diff --git a/src/Simulator/FireSimulator.cpp b/src/Simulator/FireSimulator.cpp
index ac7456b0a..927a7ae22 100644
--- a/src/Simulator/FireSimulator.cpp
+++ b/src/Simulator/FireSimulator.cpp
@@ -14,9 +14,9 @@
 
 // Easy switch for turning on debugging logging:
 #if 0
-	#define FLOG LOGD
+	#define FIRE_LOG LOGD
 #else
-	#define FLOG(...)
+	#define FIRE_LOG(...)
 #endif
 
 
@@ -111,7 +111,7 @@ void cFireSimulator::SimulateChunk(std::chrono::milliseconds a_Dt, int a_ChunkX,
 		if (!IsAllowedBlock(BlockType))
 		{
 			// The block is no longer eligible (not a fire block anymore; a player probably placed a block over the fire)
-			FLOG("FS: Removing block {%d, %d, %d}",
+			FIRE_LOG("FS: Removing block {%d, %d, %d}",
 				AbsPos.x, AbsPos.y, AbsPos.z
 			);
 			itr = Data.erase(itr);
@@ -148,14 +148,15 @@ void cFireSimulator::SimulateChunk(std::chrono::milliseconds a_Dt, int a_ChunkX,
 		}
 
 		/*
-		FLOG("FS: Fire at {%d, %d, %d} is stepping",
+		FIRE_LOG("FS: Fire at {%d, %d, %d} is stepping",
 			itr->x + a_ChunkX * cChunkDef::Width, itr->y, itr->z + a_ChunkZ * cChunkDef::Width
 		);
 		*/
 		// Has the fire burnt out?
 		if (BlockMeta == 0x0f)
 		{
-			FLOG("FS: Fire at {%d, %d, %d} burnt out, removing the fire block",
+			// The fire burnt out completely
+			FIRE_LOG("FS: Fire at {%d, %d, %d} burnt out, removing the fire block",
 				itr->x + a_ChunkX * cChunkDef::Width, itr->y, itr->z + a_ChunkZ * cChunkDef::Width
 			);
 			a_Chunk->SetBlock(x, y, z, E_BLOCK_AIR, 0);
@@ -271,7 +272,7 @@ void cFireSimulator::AddBlock(Vector3i a_Block, cChunk * a_Chunk)
 		}
 	}  // for itr - ChunkData[]
 
-	FLOG("FS: Adding block {%d, %d, %d}", a_Block.x, a_Block.y, a_Block.z);
+	FIRE_LOG("FS: Adding block {%d, %d, %d}", a_Block.x, a_Block.y, a_Block.z);
 	ChunkData.push_back(cCoordWithInt(RelX, a_Block.y, RelZ, 100));
 }
 
@@ -351,7 +352,7 @@ void cFireSimulator::TrySpreadFire(cChunk * a_Chunk, int a_RelX, int a_RelY, int
 
 				// Start the fire in the neighbor {x, y, z}
 				/*
-				FLOG("FS: Trying to start fire at {%d, %d, %d}.",
+				FIRE_LOG("FS: Trying to start fire at {%d, %d, %d}.",
 					x + a_Chunk->GetPosX() * cChunkDef::Width, y, z + a_Chunk->GetPosZ() * cChunkDef::Width
 				);
 				*/
@@ -365,7 +366,7 @@ void cFireSimulator::TrySpreadFire(cChunk * a_Chunk, int a_RelX, int a_RelY, int
 						return;
 					}
 
-					FLOG("FS: Starting new fire at {%d, %d, %d}.", a_PosX, y, a_PosZ);
+					FIRE_LOG("FS: Starting new fire at {%d, %d, %d}.", a_PosX, y, a_PosZ);
 					a_Chunk->UnboundedRelSetBlock(x, y, z, E_BLOCK_FIRE, 0);
 				}
 			}  // for y
diff --git a/src/Simulator/FloodyFluidSimulator.cpp b/src/Simulator/FloodyFluidSimulator.cpp
index 05b00c639..b5ded0c3e 100644
--- a/src/Simulator/FloodyFluidSimulator.cpp
+++ b/src/Simulator/FloodyFluidSimulator.cpp
@@ -20,9 +20,9 @@
 
 // Enable or disable detailed logging
 #if 0
-	#define FLOG LOGD
+	#define FLUID_LOG LOGD
 #else
-	#define FLOG(...)
+	#define FLUID_LOG(...)
 #endif
 
 
@@ -49,7 +49,7 @@ cFloodyFluidSimulator::cFloodyFluidSimulator(
 
 void cFloodyFluidSimulator::SimulateBlock(cChunk * a_Chunk, int a_RelX, int a_RelY, int a_RelZ)
 {
-	FLOG("Simulating block {%d, %d, %d}: block %d, meta %d",
+	FLUID_LOG("Simulating block {%d, %d, %d}: block %d, meta %d",
 		a_Chunk->GetPosX() * cChunkDef::Width + a_RelX, a_RelY, a_Chunk->GetPosZ() * cChunkDef::Width + a_RelZ,
 		a_Chunk->GetBlock(a_RelX, a_RelY, a_RelZ),
 		a_Chunk->GetMeta(a_RelX, a_RelY, a_RelZ)
@@ -61,7 +61,7 @@ void cFloodyFluidSimulator::SimulateBlock(cChunk * a_Chunk, int a_RelX, int a_Re
 	if (!IsAnyFluidBlock(MyBlock))
 	{
 		// Can happen - if a block is scheduled for simulating and gets replaced in the meantime.
-		FLOG("  BadBlockType exit");
+		FLUID_LOG("  BadBlockType exit");
 		return;
 	}
 
@@ -79,7 +79,7 @@ void cFloodyFluidSimulator::SimulateBlock(cChunk * a_Chunk, int a_RelX, int a_Re
 		{
 			// Has no tributary, has been decreased (in CheckTributaries()),
 			// no more processing needed (neighbors have been scheduled by the decrease)
-			FLOG("  CheckTributaries exit");
+			FLUID_LOG("  CheckTributaries exit");
 			return;
 		}
 	}
@@ -153,7 +153,7 @@ bool cFloodyFluidSimulator::CheckTributaries(cChunk * a_Chunk, int a_RelX, int a
 		if (IsAnyFluidBlock(a_Chunk->GetBlock(a_RelX, a_RelY + 1, a_RelZ)))
 		{
 			// This block is fed from above, no more processing needed
-			FLOG("  Fed from above");
+			FLUID_LOG("  Fed from above");
 			return false;
 		}
 	}
@@ -179,7 +179,7 @@ bool cFloodyFluidSimulator::CheckTributaries(cChunk * a_Chunk, int a_RelX, int a
 			if (IsAllowedBlock(BlockType) && IsHigherMeta(BlockMeta, a_MyMeta))
 			{
 				// This block is fed, no more processing needed
-				FLOG("  Fed from {%d, %d, %d}, type %d, meta %d",
+				FLUID_LOG("  Fed from {%d, %d, %d}, type %d, meta %d",
 					a_Chunk->GetPosX() * cChunkDef::Width + a_RelX + Coords[i].x,
 					a_RelY,
 					a_Chunk->GetPosZ() * cChunkDef::Width + a_RelZ + Coords[i].z,
@@ -193,7 +193,7 @@ bool cFloodyFluidSimulator::CheckTributaries(cChunk * a_Chunk, int a_RelX, int a
 	// Block is not fed, decrease by m_Falloff levels:
 	if (a_MyMeta >= 8)
 	{
-		FLOG("  Not fed and downwards, turning into non-downwards meta %d", m_Falloff);
+		FLUID_LOG("  Not fed and downwards, turning into non-downwards meta %d", m_Falloff);
 		a_Chunk->SetBlock(a_RelX, a_RelY, a_RelZ, m_StationaryFluidBlock, m_Falloff);
 	}
 	else
@@ -201,12 +201,12 @@ bool cFloodyFluidSimulator::CheckTributaries(cChunk * a_Chunk, int a_RelX, int a
 		a_MyMeta += m_Falloff;
 		if (a_MyMeta < 8)
 		{
-			FLOG("  Not fed, decreasing from %d to %d", a_MyMeta - m_Falloff, a_MyMeta);
+			FLUID_LOG("  Not fed, decreasing from %d to %d", a_MyMeta - m_Falloff, a_MyMeta);
 			a_Chunk->SetBlock(a_RelX, a_RelY, a_RelZ, m_StationaryFluidBlock, a_MyMeta);
 		}
 		else
 		{
-			FLOG("  Not fed, meta %d, erasing altogether", a_MyMeta);
+			FLUID_LOG("  Not fed, meta %d, erasing altogether", a_MyMeta);
 			a_Chunk->SetBlock(a_RelX, a_RelY, a_RelZ, E_BLOCK_AIR, 0);
 		}
 	}
@@ -252,7 +252,7 @@ void cFloodyFluidSimulator::SpreadToNeighbor(cChunk * a_NearChunk, int a_RelX, i
 		{
 			// Lava flowing into water, change to stone / cobblestone based on direction:
 			BLOCKTYPE NewBlock = (a_NewMeta == 8) ? E_BLOCK_STONE : E_BLOCK_COBBLESTONE;
-			FLOG("  Lava flowing into water, turning water at rel {%d, %d, %d} into stone",
+			FLUID_LOG("  Lava flowing into water, turning water at rel {%d, %d, %d} into stone",
 				a_RelX, a_RelY, a_RelZ,
 				ItemTypeToString(NewBlock).c_str()
 			);
@@ -273,7 +273,7 @@ void cFloodyFluidSimulator::SpreadToNeighbor(cChunk * a_NearChunk, int a_RelX, i
 		{
 			// Water flowing into lava, change to cobblestone / obsidian based on dest block:
 			BLOCKTYPE NewBlock = (BlockMeta == 0) ? E_BLOCK_OBSIDIAN : E_BLOCK_COBBLESTONE;
-			FLOG("  Water flowing into lava, turning lava at rel {%d, %d, %d} into %s",
+			FLUID_LOG("  Water flowing into lava, turning lava at rel {%d, %d, %d} into %s",
 				a_RelX, a_RelY, a_RelZ, ItemTypeToString(NewBlock).c_str()
 			);
 			a_NearChunk->SetBlock(a_RelX, a_RelY, a_RelZ, NewBlock, 0);
@@ -319,7 +319,7 @@ void cFloodyFluidSimulator::SpreadToNeighbor(cChunk * a_NearChunk, int a_RelX, i
 	}  // if (CanWashAway)
 
 	// Spread:
-	FLOG("  Spreading to {%d, %d, %d} with meta %d", BlockX, a_RelY, BlockZ, a_NewMeta);
+	FLUID_LOG("  Spreading to {%d, %d, %d} with meta %d", BlockX, a_RelY, BlockZ, a_NewMeta);
 	a_NearChunk->SetBlock(a_RelX, a_RelY, a_RelZ, m_FluidBlock, a_NewMeta);
 	m_World.GetSimulatorManager()->WakeUp({BlockX, a_RelY, BlockZ}, a_NearChunk);
 
@@ -332,7 +332,7 @@ void cFloodyFluidSimulator::SpreadToNeighbor(cChunk * a_NearChunk, int a_RelX, i
 
 bool cFloodyFluidSimulator::CheckNeighborsForSource(cChunk * a_Chunk, int a_RelX, int a_RelY, int a_RelZ)
 {
-	FLOG("  Checking neighbors for source creation");
+	FLUID_LOG("  Checking neighbors for source creation");
 
 	static const Vector3i NeighborCoords[] =
 	{
@@ -355,21 +355,21 @@ bool cFloodyFluidSimulator::CheckNeighborsForSource(cChunk * a_Chunk, int a_RelX
 			// Neighbor not available, skip it
 			continue;
 		}
-		// FLOG("   Neighbor at {%d, %d, %d}: %s", x, y, z, ItemToFullString(cItem(BlockType, 1, BlockMeta)).c_str());
+		// FLUID_LOG("   Neighbor at {%d, %d, %d}: %s", x, y, z, ItemToFullString(cItem(BlockType, 1, BlockMeta)).c_str());
 		if ((BlockMeta == 0) && IsAnyFluidBlock(BlockType))
 		{
 			NumNeeded--;
-			// FLOG("    Found a neighbor source at {%d, %d, %d}, NumNeeded := %d", x, y, z, NumNeeded);
+			// FLUID_LOG("    Found a neighbor source at {%d, %d, %d}, NumNeeded := %d", x, y, z, NumNeeded);
 			if (NumNeeded == 0)
 			{
 				// Found enough, turn into a source and bail out
-				// FLOG("    Found enough neighbor sources, turning into a source");
+				// FLUID_LOG("    Found enough neighbor sources, turning into a source");
 				a_Chunk->SetBlock(a_RelX, a_RelY, a_RelZ, m_FluidBlock, 0);
 				return true;
 			}
 		}
 	}
-	// FLOG("    Not enough neighbors for turning into a source, NumNeeded = %d", NumNeeded);
+	// FLUID_LOG("    Not enough neighbors for turning into a source, NumNeeded = %d", NumNeeded);
 	return false;
 }
 
diff --git a/src/Simulator/IncrementalRedstoneSimulator/CMakeLists.txt b/src/Simulator/IncrementalRedstoneSimulator/CMakeLists.txt
index 99d87ce88..15da35db0 100644
--- a/src/Simulator/IncrementalRedstoneSimulator/CMakeLists.txt
+++ b/src/Simulator/IncrementalRedstoneSimulator/CMakeLists.txt
@@ -33,5 +33,6 @@ set (HDRS
 
 if(NOT MSVC)
 	add_library(IncrementalRedstoneSimulator ${SRCS} ${HDRS})
+	target_link_libraries(IncrementalRedstoneSimulator fmt::fmt)
 endif()
 
diff --git a/src/StringUtils.cpp b/src/StringUtils.cpp
index b7e446d53..b1f58f23c 100644
--- a/src/StringUtils.cpp
+++ b/src/StringUtils.cpp
@@ -5,6 +5,8 @@
 
 #include "Globals.h"
 
+#include "fmt/printf.h"
+
 #ifdef _MSC_VER
 	// Under MSVC, link to WinSock2 (needed by RawBEToUTF8's byteswapping)
 	#pragma comment(lib, "ws2_32.lib")
@@ -50,60 +52,10 @@ static unsigned char HexToDec(char a_HexChar)
 
 
 
-AString & AppendVPrintf(AString & str, const char * format, va_list args)
+AString & Printf(AString & str, const char * format, fmt::ArgList args)
 {
 	ASSERT(format != nullptr);
-
-	char buffer[2048];
-	int len;
-	#ifdef va_copy
-	va_list argsCopy;
-	va_copy(argsCopy, args);
-	#else
-	#define argsCopy args
-	#endif
-	#ifdef _MSC_VER
-	// MS CRT provides secure printf that doesn't behave like in the C99 standard
-	if ((len = _vsnprintf_s(buffer, ARRAYCOUNT(buffer), _TRUNCATE, format, argsCopy)) != -1)
-	#else  // _MSC_VER
-	if ((len = vsnprintf(buffer, ARRAYCOUNT(buffer), format, argsCopy)) < static_cast<int>(ARRAYCOUNT(buffer)))
-	#endif  // else _MSC_VER
-	{
-		// The result did fit into the static buffer
-		#ifdef va_copy
-		va_end(argsCopy);
-		#endif
-		str.append(buffer, static_cast<size_t>(len));
-		return str;
-	}
-	#ifdef va_copy
-	va_end(argsCopy);
-	#endif
-
-	// The result did not fit into the static buffer, use a dynamic buffer:
-	#ifdef _MSC_VER
-	// for MS CRT, we need to calculate the result length
-	len = _vscprintf(format, args);
-	if (len == -1)
-	{
-		return str;
-	}
-	#endif  // _MSC_VER
-
-	// Allocate a buffer and printf into it:
-	#ifdef va_copy
-	va_copy(argsCopy, args);
-	#endif
-	std::vector<char> Buffer(static_cast<size_t>(len) + 1);
-	#ifdef _MSC_VER
-	vsprintf_s(&(Buffer.front()), Buffer.size(), format, argsCopy);
-	#else  // _MSC_VER
-	vsnprintf(&(Buffer.front()), Buffer.size(), format, argsCopy);
-	#endif  // else _MSC_VER
-	str.append(&(Buffer.front()), Buffer.size() - 1);
-	#ifdef va_copy
-	va_end(argsCopy);
-	#endif
+	str = fmt::sprintf(format, args);
 	return str;
 }
 
@@ -111,41 +63,10 @@ AString & AppendVPrintf(AString & str, const char * format, va_list args)
 
 
 
-AString & Printf(AString & str, const char * format, ...)
-{
-	str.clear();
-	va_list args;
-	va_start(args, format);
-	std::string & retval = AppendVPrintf(str, format, args);
-	va_end(args);
-	return retval;
-}
-
-
-
-
-
-AString Printf(const char * format, ...)
+AString Printf(const char * format, fmt::ArgList args)
 {
-	AString res;
-	va_list args;
-	va_start(args, format);
-	AppendVPrintf(res, format, args);
-	va_end(args);
-	return res;
-}
-
-
-
-
-
-AString & AppendPrintf(AString & dst, const char * format, ...)
-{
-	va_list args;
-	va_start(args, format);
-	std::string & retval = AppendVPrintf(dst, format, args);
-	va_end(args);
-	return retval;
+	ASSERT(format != nullptr);
+	return fmt::sprintf(format, args);
 }
 
 
@@ -690,7 +611,7 @@ are equivalent to the following loop:
 
 
 
-#define HEX(x) ((x) > 9 ? (x) + 'A' - 10 : (x) + '0')
+#define HEX(x) static_cast<char>((x) > 9 ? (x) + 'A' - 10 : (x) + '0')
 
 /**
 format binary data this way:
@@ -698,50 +619,36 @@ format binary data this way:
 */
 AString & CreateHexDump(AString & a_Out, const void * a_Data, size_t a_Size, size_t a_BytesPerLine)
 {
-	ASSERT(a_BytesPerLine <= 120);  // Due to using a fixed size line buffer; increase line[]'s size to lift this max
-	char line[512];
-	char * p;
-	char * q;
+	fmt::MemoryWriter Output;
+	/* If formatting the data from the comment above:
+		Hex holds:   "31 32 33 34 35 36 37 38 39 30 61 62 63 64 65 66 "
+		Chars holds: "1234567890abcdef" */
+	fmt::MemoryWriter Hex, Chars;
+
+	if (a_Size > 0)
+	{
+		// Same as std::ceil(static_cast<float>(a_Size) / a_BytesPerLine);
+		const size_t NumLines = a_Size / a_BytesPerLine + (a_Size % a_BytesPerLine != 0);
+		const size_t CharsPerLine = 14 + 4 * a_BytesPerLine;
+		Output.buffer().reserve(NumLines * CharsPerLine);
+	}
 
-	a_Out.reserve(a_Size / a_BytesPerLine * (18 + 6 * a_BytesPerLine));
 	for (size_t i = 0; i < a_Size; i += a_BytesPerLine)
 	{
-		size_t k = a_Size - i;
-		if (k > a_BytesPerLine)
-		{
-			k = a_BytesPerLine;
-		}
-		#ifdef _MSC_VER
-		// MSVC provides a "secure" version of sprintf()
-		int Count = sprintf_s(line, sizeof(line), "%08x:", static_cast<unsigned>(i));
-		#else
-		int Count = sprintf(line, "%08x:", static_cast<unsigned>(i));
-		#endif
-		// Remove the terminating nullptr / leftover garbage in line, after the sprintf-ed value
-		memset(line + Count, 32, sizeof(line) - static_cast<size_t>(Count));
-		p = line + 10;
-		q = p + 2 + a_BytesPerLine * 3 + 1;
+		size_t k = std::min(a_Size - i, a_BytesPerLine);
 		for (size_t j = 0; j < k; j++)
 		{
 			Byte c = (reinterpret_cast<const Byte *>(a_Data))[i + j];
-			p[0] = HEX(c >> 4);
-			p[1] = HEX(c & 0xf);
-			p[2] = ' ';
-			if (c >= ' ')
-			{
-				q[0] = static_cast<char>(c);
-			}
-			else
-			{
-				q[0] = '.';
-			}
-			p += 3;
-			q ++;
+			Hex << HEX(c >> 4) << HEX(c & 0xf) << ' ';
+			Chars << ((c >= ' ') ? static_cast<char>(c) : '.');
 		}  // for j
-		q[0] = '\n';
-		q[1] = 0;
-		a_Out.append(line);
+
+		// Write Hex with a dynamic fixed width
+		Output.write("{0:08x}: {1:{2}}   {3}\n", i, Hex.c_str(), a_BytesPerLine * 3, Chars.c_str());
+		Hex.clear();
+		Chars.clear();
 	}  // for i
+	a_Out.append(Output.data(), Output.size());
 	return a_Out;
 }
 
diff --git a/src/StringUtils.h b/src/StringUtils.h
index 12227014d..a74239ec8 100644
--- a/src/StringUtils.h
+++ b/src/StringUtils.h
@@ -22,21 +22,24 @@ typedef std::map<AString, AString> AStringMap;
 
 
 
-/** Add the formated string to the existing data in the string.
-Returns a_Dst. */
-extern AString & AppendVPrintf(AString & a_Dst, const char * format, va_list args) FORMATSTRING(2, 0);
-
 /** Output the formatted text into the string.
 Returns a_Dst. */
-extern AString & Printf       (AString & a_Dst, const char * format, ...) FORMATSTRING(2, 3);
+extern AString & Printf(AString & a_Dst, const char * format, fmt::ArgList args);
+FMT_VARIADIC(AString &, Printf, AString &, const char *)
 
 /** Output the formatted text into string
 Returns the formatted string by value. */
-extern AString Printf(const char * format, ...) FORMATSTRING(1, 2);
+extern AString Printf(const char * format, fmt::ArgList args);
+FMT_VARIADIC(AString, Printf, const char *)
 
-/** Add the formatted string to the existing data in the string.
-Returns a_Dst */
-extern AString & AppendPrintf (AString & a_Dst, const char * format, ...) FORMATSTRING(2, 3);
+/** Add the formated string to the existing data in the string.
+Returns a_Dst. */
+template <typename... Args>
+extern AString & AppendPrintf(AString & a_Dst, const char * format, const Args & ... args)
+{
+	a_Dst += Printf(format, args...);
+	return a_Dst;
+}
 
 /** Split the string at any of the listed delimiters.
 Return the splitted strings as a stringvector. */
@@ -91,8 +94,7 @@ extern AString UnicodeCharToUtf8(unsigned a_UnicodeChar);
 /** Converts a UTF-8 string into a UTF-16 BE string. */
 extern std::u16string UTF8ToRawBEUTF16(const AString & a_String);
 
-/** Creates a nicely formatted HEX dump of the given memory block.
-Max a_BytesPerLine is 120. */
+/** Creates a nicely formatted HEX dump of the given memory block. */
 extern AString & CreateHexDump(AString & a_Out, const void * a_Data, size_t a_Size, size_t a_BytesPerLine);
 
 /** Returns a copy of a_Message with all quotes and backslashes escaped by a backslash. */
diff --git a/src/UI/CMakeLists.txt b/src/UI/CMakeLists.txt
index 6477882b3..32a5af4a5 100644
--- a/src/UI/CMakeLists.txt
+++ b/src/UI/CMakeLists.txt
@@ -38,4 +38,5 @@ SET (HDRS
 
 if(NOT MSVC)
 	add_library(UI ${SRCS} ${HDRS})
+	target_link_libraries(UI fmt::fmt)
 endif()
diff --git a/src/UI/Window.cpp b/src/UI/Window.cpp
index cf02c0f00..55df04798 100644
--- a/src/UI/Window.cpp
+++ b/src/UI/Window.cpp
@@ -674,7 +674,7 @@ int cWindow::DistributeItemToSlots(cPlayer & a_Player, const cItem & a_Item, int
 {
 	if (a_LimitItems && (static_cast<size_t>(a_Item.m_ItemCount) < a_SlotNums.size()))
 	{
-		LOGWARNING("%s: Distributing less items (%d) than slots (" SIZE_T_FMT  ")", __FUNCTION__, static_cast<int>(a_Item.m_ItemCount), a_SlotNums.size());
+		LOGWARNING("%s: Distributing less items (%d) than slots (%zu)", __FUNCTION__, static_cast<int>(a_Item.m_ItemCount), a_SlotNums.size());
 		// This doesn't seem to happen with the 1.5.1 client, so we don't worry about it for now
 		return 0;
 	}
diff --git a/src/WorldStorage/CMakeLists.txt b/src/WorldStorage/CMakeLists.txt
index d9e066b32..afb3ef179 100644
--- a/src/WorldStorage/CMakeLists.txt
+++ b/src/WorldStorage/CMakeLists.txt
@@ -30,6 +30,5 @@ SET (HDRS
 
 if(NOT MSVC)
 	add_library(WorldStorage ${SRCS} ${HDRS})
-
-	target_link_libraries(WorldStorage OSSupport)
+	target_link_libraries(WorldStorage fmt::fmt OSSupport)
 endif()
diff --git a/src/WorldStorage/MapSerializer.cpp b/src/WorldStorage/MapSerializer.cpp
index c34efe507..381ef19fa 100644
--- a/src/WorldStorage/MapSerializer.cpp
+++ b/src/WorldStorage/MapSerializer.cpp
@@ -19,9 +19,9 @@ cMapSerializer::cMapSerializer(const AString & a_WorldName, cMap * a_Map):
 	m_Map(a_Map)
 {
 	AString DataPath;
-	Printf(DataPath, "%s%cdata", a_WorldName.c_str(), cFile::PathSeparator);
+	Printf(DataPath, "%s%cdata", a_WorldName.c_str(), cFile::PathSeparator());
 
-	Printf(m_Path, "%s%cmap_%i.dat", DataPath.c_str(), cFile::PathSeparator, a_Map->GetID());
+	Printf(m_Path, "%s%cmap_%i.dat", DataPath.c_str(), cFile::PathSeparator(), a_Map->GetID());
 
 	cFile::CreateFolder(FILE_IO_PREFIX + DataPath);
 }
@@ -203,9 +203,9 @@ bool cMapSerializer::LoadMapFromNBT(const cParsedNBT & a_NBT)
 cIDCountSerializer::cIDCountSerializer(const AString & a_WorldName) : m_MapCount(0)
 {
 	AString DataPath;
-	Printf(DataPath, "%s%cdata", a_WorldName.c_str(), cFile::PathSeparator);
+	Printf(DataPath, "%s%cdata", a_WorldName.c_str(), cFile::PathSeparator());
 
-	Printf(m_Path, "%s%cidcounts.dat", DataPath.c_str(), cFile::PathSeparator);
+	Printf(m_Path, "%s%cidcounts.dat", DataPath.c_str(), cFile::PathSeparator());
 
 	cFile::CreateFolder(FILE_IO_PREFIX + DataPath);
 }
diff --git a/src/WorldStorage/ScoreboardSerializer.cpp b/src/WorldStorage/ScoreboardSerializer.cpp
index 27ce36455..367b88c0d 100644
--- a/src/WorldStorage/ScoreboardSerializer.cpp
+++ b/src/WorldStorage/ScoreboardSerializer.cpp
@@ -18,9 +18,9 @@ cScoreboardSerializer::cScoreboardSerializer(const AString & a_WorldName, cScore
 	m_ScoreBoard(a_ScoreBoard)
 {
 	AString DataPath;
-	Printf(DataPath, "%s%cdata", a_WorldName.c_str(), cFile::PathSeparator);
+	Printf(DataPath, "%s%cdata", a_WorldName.c_str(), cFile::PathSeparator());
 
-	m_Path = DataPath + cFile::PathSeparator + "scoreboard.dat";
+	m_Path = DataPath + cFile::PathSeparator() + "scoreboard.dat";
 
 	cFile::CreateFolder(FILE_IO_PREFIX + DataPath);
 }
diff --git a/src/WorldStorage/StatSerializer.cpp b/src/WorldStorage/StatSerializer.cpp
index c8a4c0951..ecedd87ce 100644
--- a/src/WorldStorage/StatSerializer.cpp
+++ b/src/WorldStorage/StatSerializer.cpp
@@ -18,7 +18,7 @@ cStatSerializer::cStatSerializer(const AString & a_WorldName, const AString & a_
 	// inside the folder of the default world.
 
 	AString StatsPath;
-	Printf(StatsPath, "%s%cstats", a_WorldName.c_str(), cFile::PathSeparator);
+	Printf(StatsPath, "%s%cstats", a_WorldName.c_str(), cFile::PathSeparator());
 
 	m_LegacyPath = StatsPath + "/" + a_PlayerName + ".json";
 	m_Path = StatsPath + "/" + a_FileName + ".json";
diff --git a/src/WorldStorage/WSSAnvil.cpp b/src/WorldStorage/WSSAnvil.cpp
index 35fdaa8d8..048220a31 100755
--- a/src/WorldStorage/WSSAnvil.cpp
+++ b/src/WorldStorage/WSSAnvil.cpp
@@ -85,7 +85,7 @@ cWSSAnvil::cWSSAnvil(cWorld * a_World, int a_CompressionFactor) :
 {
 	// Create a level.dat file for mapping tools, if it doesn't already exist:
 	AString fnam;
-	Printf(fnam, "%s%clevel.dat", a_World->GetDataPath().c_str(), cFile::PathSeparator);
+	Printf(fnam, "%s%clevel.dat", a_World->GetDataPath().c_str(), cFile::PathSeparator());
 	if (!cFile::Exists(fnam))
 	{
 		cFastNBTWriter Writer;
@@ -180,7 +180,7 @@ void cWSSAnvil::ChunkLoadFailed(int a_ChunkX, int a_ChunkZ, const AString & a_Re
 {
 	// Construct the filename for offloading:
 	AString OffloadFileName;
-	Printf(OffloadFileName, "%s%cregion%cbadchunks", m_World->GetDataPath().c_str(), cFile::PathSeparator, cFile::PathSeparator);
+	Printf(OffloadFileName, "%s%cregion%cbadchunks", m_World->GetDataPath().c_str(), cFile::PathSeparator(), cFile::PathSeparator());
 	cFile::CreateFolder(FILE_IO_PREFIX + OffloadFileName);
 	auto t = time(nullptr);
 	struct tm stm;
@@ -190,7 +190,7 @@ void cWSSAnvil::ChunkLoadFailed(int a_ChunkX, int a_ChunkZ, const AString & a_Re
 		localtime_r(&t, &stm);
 	#endif
 	AppendPrintf(OffloadFileName, "%cch.%d.%d.%d-%02d-%02d-%02d-%02d-%02d.dat",
-		cFile::PathSeparator, a_ChunkX, a_ChunkZ,
+		cFile::PathSeparator(), a_ChunkX, a_ChunkZ,
 		stm.tm_year + 1900, stm.tm_mon + 1, stm.tm_mday, stm.tm_hour, stm.tm_min, stm.tm_sec
 	);
 
@@ -286,7 +286,7 @@ cWSSAnvil::cMCAFile * cWSSAnvil::LoadMCAFile(const cChunkCoords & a_Chunk)
 
 	// Load it anew:
 	AString FileName;
-	Printf(FileName, "%s%cregion", m_World->GetDataPath().c_str(), cFile::PathSeparator);
+	Printf(FileName, "%s%cregion", m_World->GetDataPath().c_str(), cFile::PathSeparator());
 	cFile::CreateFolder(FILE_IO_PREFIX + FileName);
 	AppendPrintf(FileName, "/r.%d.%d.mca", RegionX, RegionZ);
 	cMCAFile * f = new cMCAFile(*this, FileName, RegionX, RegionZ);
diff --git a/src/main.cpp b/src/main.cpp
index e1ed078e0..d75d7dc9a 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -235,6 +235,10 @@ static void UniversalMain(std::unique_ptr<cSettingsRepositoryInterface> a_Overri
 		cRoot Root;
 		Root.Start(std::move(a_OverridesRepo));
 	}
+	catch (fmt::FormatError & f)
+	{
+		FLOGERROR("Formatting exception: {0}", f.what());
+	}
 	catch (std::exception & e)
 	{
 		LOGERROR("Standard exception: %s", e.what());
@@ -447,7 +451,7 @@ static std::unique_ptr<cMemorySettingsRepository> ParseArguments(int argc, char
 	}
 	catch (const TCLAP::ArgException & exc)
 	{
-		printf("Error reading command line %s for arg %s", exc.error().c_str(), exc.argId().c_str());
+		fmt::print("Error reading command line {0} for arg {1}", exc.error(), exc.argId());
 		return cpp14::make_unique<cMemorySettingsRepository>();
 	}
 }
diff --git a/src/mbedTLS++/CMakeLists.txt b/src/mbedTLS++/CMakeLists.txt
index 18ef22312..2b7e43dce 100644
--- a/src/mbedTLS++/CMakeLists.txt
+++ b/src/mbedTLS++/CMakeLists.txt
@@ -37,8 +37,5 @@ set(HDRS
 
 if(NOT MSVC)
 	add_library(mbedTLS++ ${SRCS} ${HDRS})
-
-	if (UNIX)
-		target_link_libraries(mbedTLS++ mbedtls)
-	endif()
+	target_link_libraries(mbedTLS++ fmt::fmt mbedtls)
 endif()