diff --git a/src/ARCodeFile.cpp b/src/ARCodeFile.cpp
index 53a2386b..45583ca8 100644
--- a/src/ARCodeFile.cpp
+++ b/src/ARCodeFile.cpp
@@ -28,7 +28,7 @@ using Platform::LogLevel;
 // TODO: more user-friendly error reporting
 
 
-ARCodeFile::ARCodeFile(std::string filename)
+ARCodeFile::ARCodeFile(const std::string& filename)
 {
     Filename = filename;
 
diff --git a/src/ARCodeFile.h b/src/ARCodeFile.h
index f9a1c131..9678926d 100644
--- a/src/ARCodeFile.h
+++ b/src/ARCodeFile.h
@@ -46,7 +46,7 @@ typedef std::list<ARCodeCat> ARCodeCatList;
 class ARCodeFile
 {
 public:
-    ARCodeFile(std::string filename);
+    ARCodeFile(const std::string& filename);
     ~ARCodeFile();
 
     bool Error;
diff --git a/src/DSi_SD.cpp b/src/DSi_SD.cpp
index f3294379..59262cbd 100644
--- a/src/DSi_SD.cpp
+++ b/src/DSi_SD.cpp
@@ -769,7 +769,7 @@ void DSi_SDHost::CheckSwapFIFO()
 
 #define MMC_DESC  (Internal?"NAND":"SDcard")
 
-DSi_MMCStorage::DSi_MMCStorage(DSi_SDHost* host, bool internal, std::string filename)
+DSi_MMCStorage::DSi_MMCStorage(DSi_SDHost* host, bool internal, const std::string& filename)
     : DSi_SDDevice(host)
 {
     Internal = internal;
@@ -780,7 +780,7 @@ DSi_MMCStorage::DSi_MMCStorage(DSi_SDHost* host, bool internal, std::string file
     ReadOnly = false;
 }
 
-DSi_MMCStorage::DSi_MMCStorage(DSi_SDHost* host, bool internal, std::string filename, u64 size, bool readonly, std::string sourcedir)
+DSi_MMCStorage::DSi_MMCStorage(DSi_SDHost* host, bool internal, const std::string& filename, u64 size, bool readonly, const std::string& sourcedir)
     : DSi_SDDevice(host)
 {
     Internal = internal;
diff --git a/src/DSi_SD.h b/src/DSi_SD.h
index 5f6dbcd3..75101edc 100644
--- a/src/DSi_SD.h
+++ b/src/DSi_SD.h
@@ -125,8 +125,8 @@ protected:
 class DSi_MMCStorage : public DSi_SDDevice
 {
 public:
-    DSi_MMCStorage(DSi_SDHost* host, bool internal, std::string filename);
-    DSi_MMCStorage(DSi_SDHost* host, bool internal, std::string filename, u64 size, bool readonly, std::string sourcedir);
+    DSi_MMCStorage(DSi_SDHost* host, bool internal, const std::string& filename);
+    DSi_MMCStorage(DSi_SDHost* host, bool internal, const std::string& filename, u64 size, bool readonly, const std::string& sourcedir);
     ~DSi_MMCStorage();
 
     void Reset();
diff --git a/src/FATStorage.cpp b/src/FATStorage.cpp
index 57645246..07cf4917 100644
--- a/src/FATStorage.cpp
+++ b/src/FATStorage.cpp
@@ -37,7 +37,7 @@ namespace fs = std::filesystem;
 #endif // __WIN32__
 
 
-FATStorage::FATStorage(std::string filename, u64 size, bool readonly, std::string sourcedir)
+FATStorage::FATStorage(const std::string& filename, u64 size, bool readonly, const std::string& sourcedir)
 {
     ReadOnly = readonly;
     Load(filename, size, sourcedir);
@@ -69,7 +69,7 @@ void FATStorage::Close()
 }
 
 
-bool FATStorage::InjectFile(std::string path, u8* data, u32 len)
+bool FATStorage::InjectFile(const std::string& path, u8* data, u32 len)
 {
     if (!File) return false;
     if (FF_File) return false;
@@ -89,9 +89,10 @@ bool FATStorage::InjectFile(std::string path, u8* data, u32 len)
         return false;
     }
 
-    path = "0:/" + path;
+    std::string prefixedPath("0:/");
+    prefixedPath += path;
     FF_FIL file;
-    res = f_open(&file, path.c_str(), FA_CREATE_ALWAYS | FA_WRITE);
+    res = f_open(&file, prefixedPath.c_str(), FA_CREATE_ALWAYS | FA_WRITE);
     if (res != FR_OK)
     {
         f_unmount("0:");
@@ -345,7 +346,7 @@ void FATStorage::SaveIndex()
 }
 
 
-bool FATStorage::ExportFile(std::string path, fs::path out)
+bool FATStorage::ExportFile(const std::string& path, fs::path out)
 {
     FF_FIL file;
     FILE* fout;
@@ -393,7 +394,7 @@ bool FATStorage::ExportFile(std::string path, fs::path out)
     return true;
 }
 
-void FATStorage::ExportDirectory(std::string path, std::string outbase, int level)
+void FATStorage::ExportDirectory(const std::string& path, const std::string& outbase, int level)
 {
     if (level >= 32) return;
 
@@ -492,7 +493,7 @@ void FATStorage::ExportDirectory(std::string path, std::string outbase, int leve
     }
 }
 
-bool FATStorage::DeleteHostDirectory(std::string path, std::string outbase, int level)
+bool FATStorage::DeleteHostDirectory(const std::string& path, const std::string& outbase, int level)
 {
     if (level >= 32) return false;
 
@@ -565,7 +566,7 @@ bool FATStorage::DeleteHostDirectory(std::string path, std::string outbase, int
     return true;
 }
 
-void FATStorage::ExportChanges(std::string outbase)
+void FATStorage::ExportChanges(const std::string& outbase)
 {
     // reflect changes in the FAT volume to the host filesystem
     // * delete directories and files that exist in the index but not in the volume
@@ -652,7 +653,7 @@ bool FATStorage::CanFitFile(u32 len)
     return (freeclusters >= len);
 }
 
-bool FATStorage::DeleteDirectory(std::string path, int level)
+bool FATStorage::DeleteDirectory(const std::string& path, int level)
 {
     if (level >= 32) return false;
     if (path.length() < 1) return false;
@@ -710,7 +711,7 @@ bool FATStorage::DeleteDirectory(std::string path, int level)
     return true;
 }
 
-void FATStorage::CleanupDirectory(std::string sourcedir, std::string path, int level)
+void FATStorage::CleanupDirectory(const std::string& sourcedir, const std::string& path, int level)
 {
     if (level >= 32) return;
 
@@ -778,7 +779,7 @@ void FATStorage::CleanupDirectory(std::string sourcedir, std::string path, int l
     }
 }
 
-bool FATStorage::ImportFile(std::string path, fs::path in)
+bool FATStorage::ImportFile(const std::string& path, fs::path in)
 {
     FF_FIL file;
     FILE* fin;
@@ -825,7 +826,7 @@ bool FATStorage::ImportFile(std::string path, fs::path in)
     return true;
 }
 
-bool FATStorage::ImportDirectory(std::string sourcedir)
+bool FATStorage::ImportDirectory(const std::string& sourcedir)
 {
     // remove whatever isn't in the index
     CleanupDirectory(sourcedir, "", 0);
@@ -938,7 +939,7 @@ u64 FATStorage::GetDirectorySize(fs::path sourcedir)
     return ret;
 }
 
-bool FATStorage::Load(std::string filename, u64 size, std::string sourcedir)
+bool FATStorage::Load(const std::string& filename, u64 size, const std::string& sourcedir)
 {
     FilePath = filename;
     FileSize = size;
diff --git a/src/FATStorage.h b/src/FATStorage.h
index 29bcbc47..250f0239 100644
--- a/src/FATStorage.h
+++ b/src/FATStorage.h
@@ -31,13 +31,13 @@
 class FATStorage
 {
 public:
-    FATStorage(std::string filename, u64 size, bool readonly, std::string sourcedir);
+    FATStorage(const std::string& filename, u64 size, bool readonly, const std::string& sourcedir);
     ~FATStorage();
 
     bool Open();
     void Close();
 
-    bool InjectFile(std::string path, u8* data, u32 len);
+    bool InjectFile(const std::string& path, u8* data, u32 len);
 
     u32 ReadSectors(u32 start, u32 num, u8* data);
     u32 WriteSectors(u32 start, u32 num, u8* data);
@@ -62,19 +62,19 @@ private:
     void LoadIndex();
     void SaveIndex();
 
-    bool ExportFile(std::string path, std::filesystem::path out);
-    void ExportDirectory(std::string path, std::string outbase, int level);
-    bool DeleteHostDirectory(std::string path, std::string outbase, int level);
-    void ExportChanges(std::string outbase);
+    bool ExportFile(const std::string& path, std::filesystem::path out);
+    void ExportDirectory(const std::string& path, const std::string& outbase, int level);
+    bool DeleteHostDirectory(const std::string& path, const std::string& outbase, int level);
+    void ExportChanges(const std::string& outbase);
 
     bool CanFitFile(u32 len);
-    bool DeleteDirectory(std::string path, int level);
-    void CleanupDirectory(std::string sourcedir, std::string path, int level);
-    bool ImportFile(std::string path, std::filesystem::path in);
-    bool ImportDirectory(std::string sourcedir);
+    bool DeleteDirectory(const std::string& path, int level);
+    void CleanupDirectory(const std::string& sourcedir, const std::string& path, int level);
+    bool ImportFile(const std::string& path, std::filesystem::path in);
+    bool ImportDirectory(const std::string& sourcedir);
     u64 GetDirectorySize(std::filesystem::path sourcedir);
 
-    bool Load(std::string filename, u64 size, std::string sourcedir);
+    bool Load(const std::string& filename, u64 size, const std::string& sourcedir);
     bool Save();
 
     typedef struct
diff --git a/src/NDS.cpp b/src/NDS.cpp
index 215750f7..b5c00db1 100644
--- a/src/NDS.cpp
+++ b/src/NDS.cpp
@@ -377,7 +377,7 @@ bool NeedsDirectBoot()
     }
 }
 
-void SetupDirectBoot(std::string romname)
+void SetupDirectBoot(const std::string& romname)
 {
     if (ConsoleType == 1)
     {
diff --git a/src/NDS.h b/src/NDS.h
index dc7809e6..404e07c2 100644
--- a/src/NDS.h
+++ b/src/NDS.h
@@ -244,7 +244,7 @@ void EjectCart();
 bool CartInserted();
 
 bool NeedsDirectBoot();
-void SetupDirectBoot(std::string romname);
+void SetupDirectBoot(const std::string& romname);
 
 bool LoadGBACart(const u8* romdata, u32 romlen, const u8* savedata, u32 savelen);
 void LoadGBAAddon(int type);
diff --git a/src/NDSCart.cpp b/src/NDSCart.cpp
index 1e5a45b9..83d3bb01 100644
--- a/src/NDSCart.cpp
+++ b/src/NDSCart.cpp
@@ -232,7 +232,7 @@ void CartCommon::Reset()
     DSiMode = false;
 }
 
-void CartCommon::SetupDirectBoot(std::string romname)
+void CartCommon::SetupDirectBoot(const std::string& romname)
 {
     CmdEncMode = 2;
     DataEncMode = 2;
@@ -1217,7 +1217,7 @@ void CartHomebrew::Reset()
         SD = nullptr;
 }
 
-void CartHomebrew::SetupDirectBoot(std::string romname)
+void CartHomebrew::SetupDirectBoot(const std::string& romname)
 {
     CartCommon::SetupDirectBoot(romname);
 
@@ -1746,7 +1746,7 @@ void LoadSave(const u8* savedata, u32 savelen)
         Cart->LoadSave(savedata, savelen);
 }
 
-void SetupDirectBoot(std::string romname)
+void SetupDirectBoot(const std::string& romname)
 {
     if (Cart)
         Cart->SetupDirectBoot(romname);
diff --git a/src/NDSCart.h b/src/NDSCart.h
index b9561f0f..27182976 100644
--- a/src/NDSCart.h
+++ b/src/NDSCart.h
@@ -40,7 +40,7 @@ public:
     virtual u32 Checksum();
 
     virtual void Reset();
-    virtual void SetupDirectBoot(std::string romname);
+    virtual void SetupDirectBoot(const std::string& romname);
 
     virtual void DoSavestate(Savestate* file);
 
@@ -161,7 +161,7 @@ private:
     u8 IRCmd;
 };
 
-// CartRetailBT - Pokémon Typing Adventure (SPI BT controller)
+// CartRetailBT - Pok�mon Typing Adventure (SPI BT controller)
 class CartRetailBT : public CartRetail
 {
 public:
@@ -187,7 +187,7 @@ public:
     virtual u32 Type() override { return 0x201; }
 
     void Reset() override;
-    void SetupDirectBoot(std::string romname) override;
+    void SetupDirectBoot(const std::string& romname) override;
 
     void DoSavestate(Savestate* file) override;
 
@@ -227,7 +227,7 @@ void DecryptSecureArea(u8* out);
 
 bool LoadROM(const u8* romdata, u32 romlen);
 void LoadSave(const u8* savedata, u32 savelen);
-void SetupDirectBoot(std::string romname);
+void SetupDirectBoot(const std::string& romname);
 
 /// This function is intended to allow frontends to save and load SRAM
 /// without using melonDS APIs.
diff --git a/src/Platform.h b/src/Platform.h
index 2227ffc6..e996dea8 100644
--- a/src/Platform.h
+++ b/src/Platform.h
@@ -108,11 +108,11 @@ bool GetConfigArray(ConfigEntry entry, void* data);
 //     Looks in the user's data directory first, then the system's.
 //     If on Windows or a portable UNIX build, this simply calls OpenLocalFile().
 
-FILE* OpenFile(std::string path, std::string mode, bool mustexist=false);
-FILE* OpenLocalFile(std::string path, std::string mode);
-FILE* OpenDataFile(std::string path);
+FILE* OpenFile(const std::string& path, const std::string& mode, bool mustexist=false);
+FILE* OpenLocalFile(const std::string& path, const std::string& mode);
+FILE* OpenDataFile(const std::string& path);
 
-inline bool FileExists(std::string name)
+inline bool FileExists(const std::string& name)
 {
     FILE* f = OpenFile(name, "rb");
     if (!f) return false;
@@ -120,7 +120,7 @@ inline bool FileExists(std::string name)
     return true;
 }
 
-inline bool LocalFileExists(std::string name)
+inline bool LocalFileExists(const std::string& name)
 {
     FILE* f = OpenLocalFile(name, "rb");
     if (!f) return false;
diff --git a/src/Savestate.cpp b/src/Savestate.cpp
index 7a096176..0aa0ba37 100644
--- a/src/Savestate.cpp
+++ b/src/Savestate.cpp
@@ -49,7 +49,7 @@ using Platform::LogLevel;
 // TODO: buffering system! or something of that sort
 // repeated fread/fwrite is slow on Switch
 
-Savestate::Savestate(std::string filename, bool save)
+Savestate::Savestate(const std::string& filename, bool save)
 {
     const char* magic = "MELN";
 
diff --git a/src/Savestate.h b/src/Savestate.h
index 51f071a9..a2216ce2 100644
--- a/src/Savestate.h
+++ b/src/Savestate.h
@@ -29,7 +29,7 @@
 class Savestate
 {
 public:
-    Savestate(std::string filename, bool save);
+    Savestate(const std::string& filename, bool save);
     ~Savestate();
 
     bool Error;
diff --git a/src/frontend/qt_sdl/Platform.cpp b/src/frontend/qt_sdl/Platform.cpp
index 6b483359..f626c88d 100644
--- a/src/frontend/qt_sdl/Platform.cpp
+++ b/src/frontend/qt_sdl/Platform.cpp
@@ -288,7 +288,7 @@ bool GetConfigArray(ConfigEntry entry, void* data)
 }
 
 
-FILE* OpenFile(std::string path, std::string mode, bool mustexist)
+FILE* OpenFile(const std::string& path, const std::string& mode, bool mustexist)
 {
     QFile f(QString::fromStdString(path));
 
@@ -322,7 +322,7 @@ FILE* OpenFile(std::string path, std::string mode, bool mustexist)
     return file;
 }
 
-FILE* OpenLocalFile(std::string path, std::string mode)
+FILE* OpenLocalFile(const std::string& path, const std::string& mode)
 {
     QString qpath = QString::fromStdString(path);
 	QDir dir(qpath);
diff --git a/src/frontend/qt_sdl/ROMManager.cpp b/src/frontend/qt_sdl/ROMManager.cpp
index ac525b74..cb671e2c 100644
--- a/src/frontend/qt_sdl/ROMManager.cpp
+++ b/src/frontend/qt_sdl/ROMManager.cpp
@@ -58,7 +58,7 @@ ARCodeFile* CheatFile = nullptr;
 bool CheatsOn = false;
 
 
-int LastSep(std::string path)
+int LastSep(const std::string& path)
 {
     int i = path.length() - 1;
     while (i >= 0)
@@ -72,32 +72,45 @@ int LastSep(std::string path)
     return -1;
 }
 
-std::string GetAssetPath(bool gba, std::string configpath, std::string ext, std::string file="")
+std::string GetAssetPath(bool gba, const std::string& configpath, const std::string& ext, const std::string& file = "")
 {
+    std::string result;
+
     if (configpath.empty())
-        configpath = gba ? BaseGBAROMDir : BaseROMDir;
-
-    if (file.empty())
-    {
-        file = gba ? BaseGBAAssetName : BaseAssetName;
-        if (file.empty())
-            file = "firmware";
-    }
+        result = gba ? BaseGBAROMDir : BaseROMDir;
+    else
+        result = configpath;
 
+    // cut off trailing slashes
     for (;;)
     {
-        int i = configpath.length() - 1;
+        int i = result.length() - 1;
         if (i < 0) break;
-        if (configpath[i] == '/' || configpath[i] == '\\')
-            configpath = configpath.substr(0, i);
+        if (result[i] == '/' || result[i] == '\\')
+            result.resize(i);
         else
             break;
     }
 
-    if (!configpath.empty())
-        configpath += "/";
+    if (!result.empty())
+        result += '/';
 
-    return configpath + file + ext;
+    if (file.empty())
+    {
+        std::string& baseName = gba ? BaseGBAAssetName : BaseAssetName;
+        if (baseName.empty())
+            result += "firmware";
+        else
+            result += baseName;
+    }
+    else
+    {
+        result += file;
+    }
+
+    result += ext;
+
+    return result;
 }
 
 
@@ -288,7 +301,7 @@ bool SavestateExists(int slot)
     return Platform::FileExists(ssfile);
 }
 
-bool LoadState(std::string filename)
+bool LoadState(const std::string& filename)
 {
     // backup
     Savestate* backup = new Savestate("timewarp.mln", true);
@@ -335,7 +348,7 @@ bool LoadState(std::string filename)
     return true;
 }
 
-bool SaveState(std::string filename)
+bool SaveState(const std::string& filename)
 {
     Savestate* state = new Savestate(filename, true);
     if (state->Error)
diff --git a/src/frontend/qt_sdl/ROMManager.h b/src/frontend/qt_sdl/ROMManager.h
index 9e82a5b1..efaed36b 100644
--- a/src/frontend/qt_sdl/ROMManager.h
+++ b/src/frontend/qt_sdl/ROMManager.h
@@ -49,8 +49,8 @@ QString GBACartLabel();
 
 std::string GetSavestateName(int slot);
 bool SavestateExists(int slot);
-bool LoadState(std::string filename);
-bool SaveState(std::string filename);
+bool LoadState(const std::string& filename);
+bool SaveState(const std::string& filename);
 void UndoStateLoad();
 
 void EnableCheats(bool enable);
diff --git a/src/frontend/qt_sdl/SaveManager.cpp b/src/frontend/qt_sdl/SaveManager.cpp
index 31d2a68f..005219b8 100644
--- a/src/frontend/qt_sdl/SaveManager.cpp
+++ b/src/frontend/qt_sdl/SaveManager.cpp
@@ -25,7 +25,7 @@
 using Platform::Log;
 using Platform::LogLevel;
 
-SaveManager::SaveManager(std::string path) : QThread()
+SaveManager::SaveManager(const std::string& path) : QThread()
 {
     SecondaryBuffer = nullptr;
     SecondaryBufferLength = 0;
@@ -71,7 +71,7 @@ std::string SaveManager::GetPath()
     return Path;
 }
 
-void SaveManager::SetPath(std::string path, bool reload)
+void SaveManager::SetPath(const std::string& path, bool reload)
 {
     Path = path;
 
diff --git a/src/frontend/qt_sdl/SaveManager.h b/src/frontend/qt_sdl/SaveManager.h
index 0d38f4ba..33035ed9 100644
--- a/src/frontend/qt_sdl/SaveManager.h
+++ b/src/frontend/qt_sdl/SaveManager.h
@@ -34,11 +34,11 @@ class SaveManager : public QThread
     void run() override;
 
 public:
-    SaveManager(std::string path);
+    SaveManager(const std::string& path);
     ~SaveManager();
 
     std::string GetPath();
-    void SetPath(std::string path, bool reload);
+    void SetPath(const std::string& path, bool reload);
 
     void RequestFlush(const u8* savedata, u32 savelen, u32 writeoffset, u32 writelen);
     void CheckFlush();
diff --git a/src/frontend/qt_sdl/main.cpp b/src/frontend/qt_sdl/main.cpp
index 7015c6da..518d5f5b 100644
--- a/src/frontend/qt_sdl/main.cpp
+++ b/src/frontend/qt_sdl/main.cpp
@@ -279,7 +279,7 @@ void micClose()
     micDevice = 0;
 }
 
-void micLoadWav(std::string name)
+void micLoadWav(const std::string& name)
 {
     SDL_AudioSpec format;
     memset(&format, 0, sizeof(SDL_AudioSpec));