Improve error handling.

13 files changed, 204 insertions, 99 deletions

diff --git a/c/CMakeLists.txt b/c/CMakeLists.txt
index 0c8bb83..ccf8812 100644
--- a/c/CMakeLists.txt
+++ b/c/CMakeLists.txt
@@ -9,7 +9,7 @@ set(CMAKE_CXX_STANDARD_REQUIRED True)
 add_compile_definitions(UNICODE _UNICODE)
 
 if(NOT CMAKE_CONFIGURATION_TYPES MATCHES "Release")
-  add_compile_definitions(_DEBUG)
+  add_compile_definitions(_DEBUG NDEBUG)
 endif()
 
 add_executable(EpisodeBrowser WIN32)
@@ -24,6 +24,8 @@ target_sources(EpisodeBrowser PRIVATE
   drag.h
   episodelistview.cpp
   episodelistview.h
+  err.cpp
+  err.h
   ext.cpp
   ext.h
   listview.cpp
diff --git a/c/data.cpp b/c/data.cpp
index f862a5e..a75111a 100644
--- a/c/data.cpp
+++ b/c/data.cpp
@@ -7,28 +7,31 @@
 
 #include "data.h"
 #include "episodelistview.h"
+#include "err.h"
 #include "res.h"
 #include "util.h"
 #include "win32.h"
 #include "window.h"
 
+using namespace std::string_literals;
+
 UniqueOk<htmlParserCtxtPtr, xmlFreeParserCtxt> RemoteParserCtxt(const wchar_t* wszUrl, const char* szUrl)
 {
 	static Unique<HINTERNET, InternetCloseHandle> hi =
 		InternetOpenW(L"Episode Browser", INTERNET_OPEN_TYPE_DIRECT, nullptr, nullptr, 0);
 	if (hi.Bad(0))
-	    throw Win32Error();
+		throw Err(WINDOWS, L"Internet handle could not be opened: %s");
 
 	Unique<HINTERNET, InternetCloseHandle> hiUrl = InternetOpenUrlW(
 	    hi.v, wszUrl, nullptr, 0, INTERNET_FLAG_NO_UI, 0);
 	if (hiUrl.Bad(0))
-		throw InternetError();
+		throw Err(WININET, L"Could not open "s + wszUrl + L": %s");
 
 	char bufX[1024];
 	Unique<htmlParserCtxtPtr, xmlFreeParserCtxt> ctx = htmlCreatePushParserCtxt(
 	    nullptr, nullptr, bufX, sizeof(bufX), szUrl, XML_CHAR_ENCODING_UTF8);
 	if (ctx.Bad(0))
-		throw XmlError();
+		throw Err(LIBXML2, L"HTML parser context could not be created: %s");
 
 	htmlCtxtUseOptions(ctx.v, HTML_PARSE_RECOVER|HTML_PARSE_NOERROR|HTML_PARSE_NOWARNING);
 
@@ -37,9 +40,9 @@ UniqueOk<htmlParserCtxtPtr, xmlFreeParserCtxt> RemoteParserCtxt(const wchar_t* w
 	char bufI[1024];
 	while (r = InternetReadFile(hiUrl.v, bufI, sizeof(bufI), &cbRead), cbRead) {
 		if (!r)
-			throw InternetError();
+			throw Err(WININET, L"HTML could not be retrieved: %s");
 		if (!htmlParseChunk(ctx.v, bufI, cbRead, 0))
-			throw XmlError();
+			throw Err(LIBXML2, L"HTML could not be parsed: %s");
 	}
 	htmlParseChunk(ctx.v, bufI, 0, 1); /* Stop parsing. */
 
@@ -52,7 +55,7 @@ template <size_t N>
 bool WcharsFromXmlchars(wchar_t (&dst)[N], Unique<xmlChar*, XmlFree> utf8)
 {
 	if (utf8.Bad(0))
-		throw XmlError();
+		throw Err(LIBXML2, L"Node content could not be retrieved: %s");
 
 	/* Truncate if source is larger than destination. */
 	int lenUtf8 = xmlStrlen(utf8.v);
@@ -125,8 +128,7 @@ void WaitFor(Window& window, void (*f)(unsigned char*))
 			sig |= DONE;
 		} catch (...) {
 			sig |= DONE;
-			ShowException(L"Remote data could not be fetched due to an error while %s: %s",
-			    L"Error", MB_ICONWARNING);
+			EBMessageBox(What(), L"Remote Data Retrieval Error");
 		}
 	};
 
@@ -155,8 +157,6 @@ void WaitFor(Window& window, void (*f)(unsigned char*))
 
 void FetchData(unsigned char* sig)
 {
-	Act(L"fetching and parsing general episode data");
-
 	/* The remote data is retrieved using WinINet from the
 	 * Detective Conan World wiki. Using libxml2's "push parser",
 	 * the HTML is parsed piece by piece as it is retrieved. The
@@ -164,26 +164,26 @@ void FetchData(unsigned char* sig)
 	 * specific XPath query. This is fragile theoretically, but
 	 * unlikely to break practically. */
 
+	wchar_t url[_countof(s_window->cfg.prefixUrl)+46+1];
+	Swprintf(url, L"%shttps://www.detectiveconanworld.com/wiki/Anime", s_window->cfg.prefixUrl);
+
 	UniqueOk<htmlParserCtxtPtr, xmlFreeParserCtxt> ctx =
-		RemoteParserCtxt(L"https://www.detectiveconanworld.com/wiki/Anime",
-		    "https://www.detectiveconanworld.com/wiki/Anime");
+		RemoteParserCtxt(url, "https://www.detectiveconanworld.com/wiki/Anime");
 
 	Unique<xmlXPathContextPtr, xmlXPathFreeContext> xpathCtx = xmlXPathNewContext(ctx.v->myDoc);
 	if (xpathCtx.Bad(0))
-		throw XmlError();
+		throw Err(LIBXML2, L"XPath context could not be created: %s");
 
 	Unique<xmlXPathObjectPtr, xmlXPathFreeObject> xpathObj = xmlXPathEvalExpression(
 	    reinterpret_cast<const xmlChar*>("//tr[./td[1] != '' and ./td[3][@style='background:#f2fde9;']]"),
 	    xpathCtx.v);
 	if (xpathObj.Bad(0))
-		throw XmlError();
+		throw Err(LIBXML2, L"XPath object could not be created: %s");
 
 	xmlNodeSetPtr nodes = xpathObj.v->nodesetval;
 
 	if (!nodes || !nodes->nodeNr)
-		throw std::runtime_error("could not find remote episode information");
-
-	Act(L"inserting remote data");
+		throw Err(GENERIC, L"Data retrieval failed: No matching HTML nodes found.");
 
 	for (int i = 0; i < nodes->nodeNr; i++) {
 		if (*sig & ABORT)
@@ -191,7 +191,7 @@ void FetchData(unsigned char* sig)
 
 		const xmlNodePtr node = nodes->nodeTab[i];
 		if (xmlChildElementCount(node) != 8)
-			throw std::runtime_error("unexpected remote data format");
+			throw Err(GENERIC, L"Data retrieval failed: Unexcepted number of columns in table.");
 
 		ElvDataA& e = s_window->fvElv.At(i);
 		DlvDataA& d = s_window->fvDlv.At(i);
@@ -226,8 +226,6 @@ void FetchData(unsigned char* sig)
 
 void FetchScreenwriters(unsigned char* sig)
 {
-	Act(L"fetching and parsing screenwriter data");
-
 	/* Screenwriters are expensive to fetch, so we try to avoid
 	 * fetching screenwriters for episodes that already have a
 	 * screenwriter. Additionally, in the same session, we don't
@@ -271,13 +269,13 @@ void FetchScreenwriters(unsigned char* sig)
 		UniqueOk<htmlParserCtxtPtr, xmlFreeParserCtxt> ctx = RemoteParserCtxt(url, nullptr);
 		xpathCtx = xmlXPathNewContext(ctx.v->myDoc);
 		if (xpathCtx.Bad(0))
-			throw XmlError();
+			throw Err(LIBXML2, L"XPath context could not be created: %s");
 
 		xpathObj = xmlXPathEvalExpression(reinterpret_cast<const xmlChar*>(
 			    "//th[contains(text(), 'Screenplay:')]/following-sibling::td"),
 			    xpathCtx.v);
 		if (xpathObj.Bad(0))
-			throw XmlError();
+			throw Err(LIBXML2, L"XPath object could not be created: %s");
 
 		xmlNodeSetPtr nodes = xpathObj.v->nodesetval;
 		if (nodes && nodes->nodeNr)
diff --git a/c/data.h b/c/data.h
index 2c287a2..bbc01d2 100644
--- a/c/data.h
+++ b/c/data.h
@@ -5,9 +5,12 @@
 #include <windows.h>
 #include <libxml/xmlerror.h>
 
+#include "err.h"
 #include "util.h"
 #include "win32.h"
 
+using namespace std::string_literals;
+
 struct XmlError : public std::exception
 {
 	const char* msg;
@@ -102,6 +105,7 @@ struct FileView
 	Unique<HANDLE, CloseHandle> hf;
 	Unique<HANDLE, CloseHandle> hm;
 	Unique<T*, FreeView> view;
+	const wchar_t* filename;
 	size_t c;
 
 	static FileView Initialized(const wchar_t* filename, size_t c, size_t cInit = 0)
@@ -118,7 +122,7 @@ struct FileView
 			return {filename, c};
 	}
 
-	FileView(const wchar_t* filename, size_t c) : c(c)
+	FileView(const wchar_t* filename, size_t c) : filename(filename), c(c)
 	{
 		hf = CreateFile(filename, GENERIC_READ|GENERIC_WRITE,
 		    0, nullptr, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, nullptr);
@@ -127,9 +131,9 @@ struct FileView
 				hf = CreateFile(filename, GENERIC_READ|GENERIC_WRITE,
 				    0, nullptr, CREATE_NEW, FILE_ATTRIBUTE_NORMAL, nullptr);
 				if (hf.Bad(INVALID_HANDLE_VALUE))
-					throw Win32Error();
+					throw Err(WINDOWS, L"File "s + filename + L" could not be created: %s");
 			} else
-				throw Win32Error();
+				throw Err(WINDOWS, L"File "s + filename + L" could not be opened: %s");
 		}
 
 		LARGE_INTEGER cbMap;
@@ -137,11 +141,11 @@ struct FileView
 		hm = CreateFileMapping(hf.v, nullptr, PAGE_READWRITE,
 		    cbMap.HighPart, cbMap.LowPart, nullptr);
 		if (hm.Bad(0))
-			throw Win32Error();
+			throw Err(WINDOWS, L"File mapping for "s + filename + L" could not be created: %s");
 
 		view = reinterpret_cast<T*>(MapViewOfFile(hm.v, FILE_MAP_ALL_ACCESS, 0, 0, 0));
 		if (view.Bad(0))
-			throw Win32Error();
+			throw Err(WINDOWS, L"View for "s + filename + L"could not be mapped: %s");
 	}
 
 	/* Access element by index, performing bounds check and, if
@@ -150,7 +154,8 @@ struct FileView
 	T& At(size_t i)
 	{
 		if (i >= c)
-			throw std::out_of_range("index larger than buffer");
+			throw Err(GENERIC, L"Element in "s + filename +
+			    L" could not be accessed: Index larger than buffer.");
 
 		T& t = view.v[i];
 
@@ -159,7 +164,8 @@ struct FileView
 				T t_;
 				memcpy(&t, &t_, sizeof(T));
 			} else if (t.version != Version<T>)
-				throw std::runtime_error("invalid struct version");
+				throw Err(GENERIC, L"Element in "s + filename +
+				    L" could not be accessed: Invalid format version.");
 		}
 
 		/* TODO: Use a custom exception type that informs the
diff --git a/c/debug.cpp b/c/debug.cpp
index 3e20d73..39dfb5d 100644
--- a/c/debug.cpp
+++ b/c/debug.cpp
@@ -3,6 +3,7 @@
 #include <windows.h>
 
 #include "debug.h"
+#include "err.h"
 #include "win32.h"
 
 struct Avg {
@@ -19,17 +20,17 @@ Benchmark::Benchmark(const char* const name, const int id, const int avgmax)
 {
 	if (!freq) {
 		if (!QueryPerformanceFrequency(&liFreq))
-			throw Win32Error();
+			throw Err(WINDOWS, L"Tick frequency could not be queried: %s");
 		freq = liFreq.QuadPart;
 	}
 
 	LARGE_INTEGER liTicks;
 	if (!QueryPerformanceCounter(&liTicks))
-		throw Win32Error();
+		throw Err(WINDOWS, L"Ticks could not be retrieved: %s");
 	ticks = liTicks.QuadPart;
 }
 
-void Benchmark::Disable()
+void Benchmark::Disable() noexcept
 {
 	disabled = true;
 }
@@ -66,7 +67,7 @@ Benchmark::~Benchmark()
 	}
 }
 
-const char* WmName(const UINT uMsg)
+const char* WmName(const UINT uMsg) noexcept
 {
 	static const UINT vKey[] = {
 		0, 1, 2, 3, 5, 6, 7, 8, 10, 11, 12, 13, 14, 15, 16, 17, 18,
diff --git a/c/debug.h b/c/debug.h
index e9cefa3..9a201a7 100644
--- a/c/debug.h
+++ b/c/debug.h
@@ -13,7 +13,7 @@ struct Benchmark
 	~Benchmark();
 
 	/* Don't print time on destruction. */
-	void Disable();
+	void Disable() noexcept;
 
 	long long ticks;
 	bool disabled = false;
@@ -23,6 +23,6 @@ struct Benchmark
 };
 
 /* Return name of given window message (WM_*). */
-const char* WmName(UINT uMsg);
+const char* WmName(UINT uMsg) noexcept;
 
 #endif
diff --git a/c/err.cpp b/c/err.cpp
new file mode 100644
index 0000000..fd35ddd
--- /dev/null
+++ b/c/err.cpp
@@ -0,0 +1,87 @@
+#include <exception>
+#include <windows.h>
+#include <wininet.h>
+#include <libxml/xmlerror.h>
+
+#include "err.h"
+#include "util.h"
+#include "win32.h"
+
+Err::Err(ErrType t, const wchar_t* fmt)
+{
+	switch (t) {
+	case GENERIC:
+		what = fmt;
+		break;
+	case WINDOWS:
+	    {
+		wchar_t* msg;
+		DWORD lenMsg = FormatMessageW(
+		    FORMAT_MESSAGE_ALLOCATE_BUFFER
+		    |FORMAT_MESSAGE_FROM_SYSTEM
+		    |FORMAT_MESSAGE_IGNORE_INSERTS,
+		    nullptr,
+		    GetLastError(),
+		    MAKELANGID(LANG_ENGLISH, SUBLANG_ENGLISH_US),
+		    (wchar_t*)&msg,
+		    0, nullptr);
+		what = std::wstring(lenMsg+wcslen(fmt), 0);
+		Swprintf(what, fmt, msg);
+		HeapFree(GetProcessHeap(), 0, msg);
+		break;
+	    }
+	case WININET:
+	    {
+		DWORD code = GetLastError();
+		if (code == ERROR_INTERNET_EXTENDED_ERROR) {
+			DWORD lenMsg;
+			InternetGetLastResponseInfo(&code, nullptr, &lenMsg);
+			std::wstring msg(lenMsg, 0);
+			if (InternetGetLastResponseInfoW(&code, msg.data(), &lenMsg)) {
+				what = std::wstring(lenMsg+wcslen(fmt), 0);
+				Swprintf(what, fmt, msg.c_str());
+				EBMessageBox(msg, L"Test");
+			} else
+				what = Err(WINDOWS, fmt).what;
+		} else {
+			wchar_t* wszMsg;
+			DWORD lenMsg = FormatMessageW(
+			    FORMAT_MESSAGE_ALLOCATE_BUFFER
+			    |FORMAT_MESSAGE_FROM_SYSTEM
+			    |FORMAT_MESSAGE_FROM_HMODULE
+			    |FORMAT_MESSAGE_IGNORE_INSERTS,
+			    GetModuleHandle(L"wininet.dll"),
+			    code,
+			    MAKELANGID(LANG_ENGLISH, SUBLANG_ENGLISH_US),
+			    (wchar_t*)&wszMsg,
+			    0, nullptr);
+			what = std::wstring(lenMsg+wcslen(fmt), 0);
+			Swprintf(what, fmt, wszMsg);
+			HeapFree(GetProcessHeap(), 0, wszMsg);
+		}
+		break;
+	    }
+	case LIBXML2:
+	    {
+		std::wstring msg = WideFromNarrow(xmlGetLastError()->message);
+		what = std::wstring(msg.size()+wcslen(fmt), 0);
+		Swprintf(what, fmt, msg.c_str());
+		break;
+	    }
+	}
+}
+
+std::wstring What(std::exception_ptr ex)
+{
+	try {
+		std::rethrow_exception(ex);
+	} catch (const Err& e) {
+		return e.what;
+	} catch (const WideException& e) {
+		return e.What();
+	} catch (const std::exception& e) {
+		return WideFromNarrow(e.what());
+	} catch (...) {
+		return L"Unknown exception";
+	}
+}
diff --git a/c/err.h b/c/err.h
new file mode 100644
index 0000000..d4a9976
--- /dev/null
+++ b/c/err.h
@@ -0,0 +1,25 @@
+#ifndef ERR_H
+#define ERR_H
+
+#include <exception>
+#include <string>
+
+enum ErrType : unsigned char
+{
+	GENERIC,
+	WINDOWS,
+	WININET,
+	LIBXML2
+};
+
+struct Err
+{
+	std::wstring what;
+	Err(ErrType t, const wchar_t* fmt = L"%s");
+	inline Err(ErrType t, std::wstring fmt) : Err(t, fmt.c_str()) {}
+};
+
+/* Return a wide string describing exception. */
+std::wstring What(std::exception_ptr e = std::current_exception());
+
+#endif
diff --git a/c/ext.cpp b/c/ext.cpp
index ea6718a..ab47ab4 100644
--- a/c/ext.cpp
+++ b/c/ext.cpp
@@ -12,7 +12,7 @@ bool OpenOnline(const CfgA& cfg, int iEp)
 	INT_PTR r = reinterpret_cast<INT_PTR>(
 	    ShellExecuteW(nullptr, L"open", url, nullptr, nullptr, SW_SHOWNORMAL));
 	if (r <= 32)
-		throw Win32Error();
+		throw Err(WINDOWS, L"Address "s + url + L" could not be opened: %s");
 	return true;
 }
 
@@ -23,7 +23,7 @@ bool OpenWiki(const DlvDataA& d)
 	INT_PTR r = reinterpret_cast<INT_PTR>(
 	    ShellExecuteW(nullptr, L"open", url, nullptr, nullptr, SW_SHOWNORMAL));
 	if (r <= 32)
-		throw Win32Error();
+		throw Err(WINDOWS, L"Address "s + url + L" could not be opened: %s");
 	return true;
 }
 
@@ -84,7 +84,7 @@ static bool FindMatchingFile(wchar_t (&file)[MAX_PATH], const wchar_t* const roo
 	WIN32_FIND_DATA fdata;
 	Unique<HANDLE, FindClose> h = FindFirstFileW(pat, &fdata);
 	if (h.Bad(INVALID_HANDLE_VALUE))
-		throw Win32Error();
+		throw Err(WINDOWS, L"Directory "s + root + L" could not be traversed: %s");
 
 	do
 		if (fdata.cFileName[0] == L'.')
@@ -102,7 +102,7 @@ static bool FindMatchingFile(wchar_t (&file)[MAX_PATH], const wchar_t* const roo
 	while (FindNextFileW(h.v, &fdata));
 
 	if (GetLastError() != ERROR_NO_MORE_FILES)
-		throw Win32Error();
+		throw Err(WINDOWS, L"Next file in "s + root + L" could not be accessed: %s");
 
 	return false;
 }
@@ -114,7 +114,7 @@ bool OpenLocally(CfgA& cfg, const ElvDataA& e)
 		INT_PTR r = reinterpret_cast<INT_PTR>(
 		    ShellExecuteW(nullptr, L"open", file, nullptr, nullptr, SW_SHOWNORMAL));
 		if (r <= 32)
-			throw Win32Error();
+			throw Err(WINDOWS, L"File "s + file + L" could not be opened: %s");
 		return true;
 	} else
 		return false;
diff --git a/c/main.cpp b/c/main.cpp
index 9e8cee3..f9d4a42 100644
--- a/c/main.cpp
+++ b/c/main.cpp
@@ -126,13 +126,11 @@ static void InitializeMainWindow_(const HWND hWnd)
 	 * initializes global variables that are used by WndProc. */
 
 	/* Look up DPI. */
-	Act(L"looking up DPI");
 	if (auto lib = Library::Maybe(L"User32.dll");
 	    auto GetDpiForWindow = lib? lib->GetProcAddress<UINT(HWND)>("GetDpiForWindow"): nullptr)
 		g_dpi = GetDpiForWindow(hWnd);
 
 	/* Load normal font. */
-	Act(L"loading fonts");
 	if (auto lib = Library::Maybe(L"User32.dll");
 	    lib && lib->GetProcAddress<void>("SystemParametersInfoW")) {
 		NONCLIENTMETRICSW m = {sizeof(NONCLIENTMETRICSW)};
@@ -160,7 +158,6 @@ static void InitializeMainWindow_(const HWND hWnd)
 		SetWindowTheme = (decltype(SetWindowTheme))(void*)GetProcAddress(hModule, "SetWindowTheme");
 	}
 
-	Act(L"setting up main window");
 	g_window = new Window(hWnd);
 }
 
@@ -169,18 +166,17 @@ void InitializeMainWindow(const HWND hWnd) noexcept
 	try {
 		InitializeMainWindow_(hWnd);
 	} catch (...) {
-		ShowException(L"Initialization failed due to an error while %s: %s");
+		EBMessageBox(What(), L"Initialization Error", MB_ICONERROR);
 		exit(1);
 	}
 }
 
 LRESULT CALLBACK WndProc(const HWND hWnd, const UINT uMsg, const WPARAM wParam, const LPARAM lParam)
 {
-	Act(nullptr);
 	try {
 		return g_window->WndProc(hWnd, uMsg, wParam, lParam);
 	} catch (...) {
-		ShowException(L"The action was cancelled due to an error while %s: %s");
+		EBMessageBox(What(), L"Error");
 	}
 	return DefWindowProc(hWnd, uMsg, wParam, lParam);
 }
@@ -223,7 +219,6 @@ LRESULT CALLBACK Window::WndProc(const HWND hWnd, const UINT uMsg, const WPARAM
 {
 	switch (uMsg) {
 	case WM_CREATE:
-		Act(L"creating main window");
 		UpdateTheme();
 		SetWindowPos(hWnd, nullptr, -1, -1, Dpi(510), Dpi(412), SWP_NOZORDER|SWP_NOMOVE|SWP_NOACTIVATE);
 		SetFocus(elv.hWnd);
diff --git a/c/test.cpp b/c/test.cpp
index 21f52f4..e7c23e5 100644
--- a/c/test.cpp
+++ b/c/test.cpp
@@ -112,6 +112,31 @@ TESTS
 // #undef CPY
 // #undef SCPY
 // 	}
+
+	TEST(NewCfg)
+	{
+		FileView<CfgA> fv2 = FileView<CfgA>::Initialized(L"cfg2.dat", 1);
+		CfgA* a = &s_window->cfg;
+		CfgA* b = fv2+0;
+
+#define CPY(member) b->member = a->member;
+#define SCPY(member) Wcscpy(b->member, a->member);
+
+		CPY(bViewWatched);
+		CPY(bViewTVOriginal);
+		CPY(iSortCol);
+		CPY(cEp);
+		CPY(iFocus);
+		CPY(heightDlv);
+		SCPY(limitToScreenwriter);
+		SCPY(root);
+		SCPY(glob);
+		SCPY(url);
+		Swprintf(b->prefixUrl, L"http://localhost:8000/?u=");
+
+#undef CPY
+#undef SCPY
+	}
 };
 
 int RunTests(Window& window)
@@ -121,7 +146,7 @@ int RunTests(Window& window)
 	const Test tests[] = {
 		StrcpyWithSmallerDestination(),
 		//IO(),
-		// MigrateCfg(),
+		//NewCfg(),
 	};
 
 	printf("Results (%llu tests):\n", sizeof(tests)/sizeof(*tests));
diff --git a/c/util.h b/c/util.h
index da77ff9..668d040 100644
--- a/c/util.h
+++ b/c/util.h
@@ -1,10 +1,12 @@
 #ifndef UTIL_H
 #define UTIL_H
 
+#include <cassert>
 #include <cstring>
 #include <memory>
 #include <stdexcept>
 #include <string>
+#include <type_traits>
 #include <windows.h>
 
 #define CONCAT_IMPL(a, b) a##b
@@ -14,9 +16,7 @@
 #define SET_TERMINATE							\
 	std::set_terminate([]() noexcept				\
 	{								\
-		ShowException(						\
-		    L"Episode Browser was terminated due to an error while %s: %s", \
-		    L"Fatal Error", MB_ICONERROR);			\
+		EBMessageBox(What(), L"Fatal Error", MB_ICONERROR);	\
 		_Exit(1);						\
 	})
 
@@ -98,14 +98,12 @@ struct UniqueOk
 	T v;
 	UniqueOk(Unique<T, F>&& u) : v(std::move(u.v))
 	{
-		if (!u.ok)
-			throw std::runtime_error("cannot construct UniqueOk from non-ok Unique");
+		assert(u.ok, "UniqueOk may not be constructed from non-ok Unique");
 		u.ok = false;
 	}
 	UniqueOk& operator =(Unique<T, F>&& u)
 	{
-		if (!u.ok)
-			throw std::runtime_error("cannot construct UniqueOk from non-ok Unique");
+		assert(u.ok, "UniqueOk may not be constructed from non-ok Unique");
 		F(v);
 		v = std::move(u.v);
 		u.ok = false;
@@ -153,14 +151,16 @@ inline size_t Len(T (&)[N])
 
 /* Format wide string. */
 template<typename... T>
-inline int Swprintf(Buf<wchar_t> buf, const wchar_t* const fmt, T... xs)
+inline std::enable_if_t<!std::disjunction_v<std::is_class<T>...>, int>
+Swprintf(Buf<wchar_t> buf, const wchar_t* const fmt, T... xs)
 {
 	return _snwprintf_s(buf, buf.c, _TRUNCATE, fmt, xs...);
 }
 
 /* Format static narrow string. */
 template<typename... T>
-inline int Sprintf(Buf<char> buf, const char* const fmt, T... xs)
+inline std::enable_if_t<!std::disjunction_v<std::is_class<T>...>, int>
+Sprintf(Buf<char> buf, const char* const fmt, T... xs)
 {
 	return _snprintf_s(buf, buf.c, _TRUNCATE, fmt, xs...);
 }
diff --git a/c/win32.cpp b/c/win32.cpp
index 2686f2e..2ecea50 100644
--- a/c/win32.cpp
+++ b/c/win32.cpp
@@ -4,6 +4,7 @@
 #include <windows.h>
 #include <wininet.h>
 
+#include "err.h"
 #include "util.h"
 #include "win32.h"
 #include "window.h"
@@ -16,7 +17,7 @@ std::wstring WideFromNarrow(const std::string_view src, const int cp)
 	int cchWide = MultiByteToWideChar(cp, 0, src.data(), cchNarrow, nullptr, 0);
 	std::wstring dst(cchWide, 0);
 	if (!MultiByteToWideChar(cp, 0, src.data(), cchNarrow, dst.data(), cchWide))
-		throw Win32Error();
+		throw Err(WINDOWS, L"Narrow string could not be converted to wide string: %s");
 	return dst;
 }
 
@@ -95,34 +96,6 @@ int EBMessageBox(const std::wstring_view text, const std::wstring_view caption,
 	return MessageBox(hWnd, text.data(), caption.data(), uType);
 }
 
-void Act(const wchar_t* action)
-{
-	s_action = action;
-}
-
-void ShowException(const wchar_t* const fmt, const wchar_t* const title, const UINT uType) noexcept
-{
-	if (!s_action)
-		s_action = L"performing an unknown action";
-	try {
-		std::rethrow_exception(std::current_exception());
-	} catch (const WideException& e) {
-		std::wstring msg(wcslen(fmt)+wcslen(s_action)+wcslen(e.What()), 0);
-		Swprintf(msg, fmt, s_action, e.What());
-		EBMessageBox(msg, title, uType);
-	} catch (const std::exception& e) {
-		std::wstring what = WideFromNarrow(e.what());
-		std::wstring msg(wcslen(fmt)+wcslen(s_action)+what.length(), 0);
-		Swprintf(msg, fmt, s_action, what.c_str());
-		EBMessageBox(msg, title, uType);
-	} catch (...) {
-		const wchar_t* what = L"an unknown error occurred";
-		std::wstring msg(wcslen(fmt)+wcslen(s_action)+wcslen(what), 0);
-		Swprintf(msg, fmt, s_action, what);
-		EBMessageBox(msg, title, uType);
-	}
-}
-
 int GetRelativeCursorPos(const HWND hWnd, POINT* const pt) noexcept
 {
 	RECT rc;
@@ -229,7 +202,7 @@ Library::Library(const wchar_t* const lib)
 {
 	m_hModule = LoadLibraryW(lib);
 	if (!m_hModule)
-		throw Win32Error();
+		throw Err(WINDOWS, L"Library "s + lib + L" could not be loaded: %s");
 }
 
 Library::~Library()
diff --git a/c/win32.h b/c/win32.h
index a88e97c..c18e70f 100644
--- a/c/win32.h
+++ b/c/win32.h
@@ -6,6 +6,8 @@
 #include <windows.h>
 #include <commctrl.h>
 
+#include "err.h"
+
 /* Convert narrow to wide string. */
 std::wstring WideFromNarrow(const std::string_view src, const int cp = CP_UTF8);
 
@@ -13,16 +15,7 @@ std::wstring WideFromNarrow(const std::string_view src, const int cp = CP_UTF8);
 void WithNextWindow(void (*proc)(HWND));
 
 /* Display message box centered in main window. */
-int EBMessageBox(std::wstring_view text, std::wstring_view data, UINT uType);
-
-/* Specify current action (used by ShowException). */
-void Act(const wchar_t* action);
-
-/* Show message box for current exception. */
-void ShowException(
-    const wchar_t* fmt = L"An error occurred: %s",
-    const wchar_t* title = L"Error",
-    UINT uType = MB_ICONWARNING) noexcept;
+int EBMessageBox(std::wstring_view text, std::wstring_view data, UINT uType = MB_ICONWARNING);
 
 /* Retrieve mouse position relative to given window's client area. */
 int GetRelativeCursorPos(HWND hWnd, POINT* pt) noexcept;
@@ -89,7 +82,7 @@ T* Library::GetProcAddress(const char* const szProc) noexcept
 template <typename T>
 inline T Require(const T x)
 {
-	if (!x) throw Win32Error();
+	if (!x) Err(WINDOWS, L"System error: %s");
 	return x;
 }