Add wstring_owner, replacing std::wstring.

std::basic_string is nice, but it is not very ergonomic if everything
you really need is to automatically free C strings at end of scope.

I suppose I could have used std::unique_ptr for this, but I suspect
the ergonomics would be worse.

7 files changed, 103 insertions, 53 deletions

diff --git a/c/common.cpp b/c/common.cpp
index bc2d4af..614bfeb 100644
--- a/c/common.cpp
+++ b/c/common.cpp
@@ -2,6 +2,59 @@
 
 #include "common.h"
 
+/* wstring_owner: Simple wrapper for wide C strings. */
+
+wstring_owner::wstring_owner() {}
+
+wstring_owner::wstring_owner(wchar_t* const wsz) : p(wsz) {}
+
+wstring_owner& wstring_owner::operator=(wchar_t* const wsz)
+{
+	if (p != wsz) {
+		delete p;
+		p = wsz;
+	}
+	return *this;
+}
+
+wstring_owner::wstring_owner(wstring_owner&& wso) noexcept : p(std::exchange(wso.p, nullptr)) {}
+
+wstring_owner& wstring_owner::operator=(wstring_owner&& wso) noexcept
+{
+	std::swap(p, wso.p);
+	return *this;
+}
+
+/* Return pointer, releasing ownership. */
+wchar_t* wstring_owner::release()
+{
+	wchar_t* p2 = p;
+	p = nullptr;
+	return p2;
+}
+
+wstring_owner::operator bool() const
+{
+	return p;
+}
+
+wstring_owner::~wstring_owner()
+{
+	delete p;
+}
+
+wstring_owner WsoFromSz(const char* const sz, const int iCp)
+{
+	int cbMultiByte = strlen(sz)+1;
+	int cchWideChar = MultiByteToWideChar(iCp, 0, sz, cbMultiByte, NULL, 0);
+	wchar_t* wsz = new wchar_t[cchWideChar];
+	if (!MultiByteToWideChar(iCp, 0, sz, cbMultiByte, wsz, cchWideChar)) {
+		delete wsz;
+		throw Win32Error(GetLastError());
+	}
+	return wsz;
+}
+
 /* Win32Error: Exception for Windows API errors. */
 
 Win32Error::Win32Error() : dwErr(GetLastError()) {}
@@ -55,17 +108,6 @@ Library::~Library()
 	FreeLibrary(m_hModule);
 }
 
-/* Convert narrow unmanaged string to wide managed string. */
-std::wstring WsFromSz(const char* sz, int iCp)
-{
-	int cbMultiByte = strlen(sz)+1;
-	int cchWideChar = MultiByteToWideChar(iCp, 0, sz, cbMultiByte, NULL, 0);
-	std::wstring ws(cchWideChar, 0);
-	if (!MultiByteToWideChar(iCp, 0, sz, cbMultiByte, ws.data(), cchWideChar))
-		throw Win32Error(GetLastError());
-	return ws;
-}
-
 /* Move message box to center of main window. */
 static LRESULT CALLBACK CBTProc(const int nCode, const WPARAM wParam, const LPARAM lParam) noexcept
 {
diff --git a/c/common.h b/c/common.h
index 8b88635..7b7e996 100644
--- a/c/common.h
+++ b/c/common.h
@@ -11,7 +11,22 @@
 #define WA "A"
 #endif
 
-std::wstring WsFromSz(const char* sz, int iCp = CP_UTF8);
+struct wstring_owner
+{
+	wstring_owner();
+	wstring_owner(wchar_t* wsz);
+	wstring_owner& operator=(wchar_t* wsz);
+	wstring_owner(wstring_owner& wso) = delete;
+	wstring_owner& operator=(wstring_owner& wso) = delete;
+	wstring_owner(wstring_owner&& wso) noexcept;
+	wstring_owner& operator=(wstring_owner&& wso) noexcept;
+	wchar_t *release();
+	operator bool() const;
+	~wstring_owner();
+	wchar_t* p = nullptr;
+};
+
+wstring_owner WsoFromSz(const char* sz, int iCp = CP_UTF8);
 int EBMessageBox(const wchar_t* wszText, const wchar_t* wszCaption, unsigned uType);
 
 struct Win32Error : public std::exception
diff --git a/c/datalistview.cpp b/c/datalistview.cpp
index ea68f2d..02a399f 100644
--- a/c/datalistview.cpp
+++ b/c/datalistview.cpp
@@ -54,20 +54,20 @@ void DataListView::ShowEpisode(const int iEpisode)
 	LVITEM lviValue = {LVIF_TEXT};
 
 	for (int i = 0; q.NextSolution(std::nothrow); i++) {
-		std::wstring wsKey;
-		std::wstring wsValue;
+		wstring_owner wsoKey;
+		wstring_owner wsoValue;
 
-		if (!(PlGet(t+1, &wsKey) && PlGet(t+2, &wsValue)))
+		if (!(PlGet(t+1, &wsoKey) && PlGet(t+2, &wsoValue)))
 			continue;
 
 		lviKey.iItem = i;
 		lviKey.iSubItem = 0;
-		lviKey.pszText = wsKey.data();
+		lviKey.pszText = wsoKey.p;
 		ListView_InsertItem(hWnd, &lviKey);
 
 		lviValue.iItem = i;
 		lviValue.iSubItem = 1;
-		lviValue.pszText = wsValue.data();
+		lviValue.pszText = wsoValue.p;
 		ListView_SetItem(hWnd, &lviValue);
 	}
 
diff --git a/c/episodelistview.cpp b/c/episodelistview.cpp
index b3ee02f..132941c 100644
--- a/c/episodelistview.cpp
+++ b/c/episodelistview.cpp
@@ -272,16 +272,16 @@ int CALLBACK EpisodeListView::SortProc(const LPARAM iItem1, const LPARAM iItem2,
 	case ELVSITITLE:
 	    {
 		Mark m;
-		std::wstring ws1, ws2;
+		wstring_owner wso1, wso2;
 		int cch, cch1, cch2;
-		if (!Pl("episode_data","episode_title",lvi1.lParam,&ws1))
+		if (!Pl("episode_data","episode_title",lvi1.lParam,&wso1))
 			return 0;
-		if (!Pl("episode_data","episode_title",lvi2.lParam,&ws2))
+		if (!Pl("episode_data","episode_title",lvi2.lParam,&wso2))
 			return 0;
-		cch1 = wcslen(ws1.c_str());
-		cch2 = wcslen(ws2.c_str());
+		cch1 = wcslen(wso1.p);
+		cch2 = wcslen(wso2.p);
 		cch = cch1 > cch2? cch2: cch1;
-		return iOrder*_wcsnicmp(ws1.c_str(), ws2.c_str(), cch);
+		return iOrder*_wcsnicmp(wso1.p, wso2.p, cch);
 	    }
 	default:
 		return 0;
@@ -412,12 +412,12 @@ void EpisodeListView::Update()
 /* Update episode name and rating. */
 void EpisodeListView::UpdateItem(const LVITEM* const pLvi)
 {
-	std::wstring wsName;
-	if (!Pl("episode_data","episode_title",pLvi->lParam,&wsName)) {
+	wstring_owner wsoName;
+	if (!Pl("episode_data","episode_title",pLvi->lParam,&wsoName)) {
 		if (!Pl("episode_data","update_episode_data")) goto r;
-		if (!Pl("episode_data","episode_title",pLvi->lParam,&wsName)) goto r;
+		if (!Pl("episode_data","episode_title",pLvi->lParam,&wsoName)) goto r;
 	}
-	ListView_SetItemText(hWnd, pLvi->iItem, ELVSITITLE, wsName.data());
+	ListView_SetItemText(hWnd, pLvi->iItem, ELVSITITLE, wsoName.p);
 
 r:	int iRating;
 	if (!Pl("episode_data","episode_rating",pLvi->lParam,&iRating)) {
diff --git a/c/main.cpp b/c/main.cpp
index c9be01d..2edc6ec 100644
--- a/c/main.cpp
+++ b/c/main.cpp
@@ -48,7 +48,7 @@ void TerminateMsg(const wchar_t* wsz1, const wchar_t* wsz2) noexcept
 {
 	wchar_t wsz[256] = {0};
 	if (wsz2)
-		wszf(wsz, L"Episode Browser was terminated due to %s: %s.", wsz1, wsz2);
+		wszf(wsz, L"Episode Browser was terminated due to %s: %s", wsz1, wsz2);
 	else
 		wszf(wsz, L"Episode Browser was terminated due to %s.", wsz1);
 	MessageBox(g_hWnd, wsz, L"Fatal Error", MB_ICONERROR);
@@ -59,15 +59,14 @@ void OnTerminate() noexcept
 	try {
 		std::rethrow_exception(std::current_exception());
         } catch (const term_t& t) {
-		std::wstring ws;
-		if (PlString(t, &ws))
-			TerminateMsg(L"a Prolog exception", ws.c_str());
+		if (auto wso = PlString(t))
+			TerminateMsg(L"a Prolog exception", wso.p);
 		else
 			TerminateMsg(L"a Prolog exception", NULL);
 	} catch (const Win32Error& e) {
 		TerminateMsg(L"a Windows error", e.WhatW());
 	} catch (const std::exception& e) {
-		TerminateMsg(L"an exception", WsFromSz(e.what()).c_str());
+		TerminateMsg(L"an exception", WsoFromSz(e.what()).p);
 	} catch (...) {
 		TerminateMsg(L"an exception", NULL);
 	}
@@ -466,13 +465,13 @@ void WaitFor(const char* szMod, const char* szPred)
 	static atom_t aThread;
 	static int bActive;
 	static int iTimer;
-	static std::wstring wsPred;
+	static wstring_owner wsoPred;
 
 	if (bActive) {
-		wchar_t wsz[128] = {0};
+		wchar_t wsz[256] = {0};
 		wszf(wsz, L"Another task (%s) is active. "
 		    L"Do you want to cancel the existing task and start a new one?",
-		    wsPred.c_str());
+		    wsoPred.p);
 		if (EBMessageBox(wsz, L"Error", MB_YESNO|MB_ICONWARNING) != IDYES)
 			return;
 		KillTimer(NULL, iTimer);
@@ -483,7 +482,8 @@ void WaitFor(const char* szMod, const char* szPred)
 	/* The timer procedure animates an ellipsis in the status bar
 	 * while the thread is running. */
 
-	static auto proc = [](HWND, UINT, UINT_PTR, DWORD) -> void {
+	static auto proc = [](HWND, UINT, UINT_PTR, DWORD) -> void
+	{
 		static int i = 0;
 
 		if (Pl("episode_data","thread_running",aThread)) {
@@ -501,7 +501,7 @@ void WaitFor(const char* szMod, const char* szPred)
 	Plx(szMod,"thread_create",szPred,&aThread);
 	SendMessage(g_hWndStatus, SB_SETTEXT, MAKEWPARAM(1,0), (LPARAM)L".");
 	if (prefer(iTimer = SetTimer(NULL, -1, 500, proc))) {
-		wsPred = WsFromSz(szPred);
+		wsoPred = WsoFromSz(szPred);
 		bActive = 1;
 	}
 }
diff --git a/c/pl.cpp b/c/pl.cpp
index 665fe3a..1255609 100644
--- a/c/pl.cpp
+++ b/c/pl.cpp
@@ -90,10 +90,11 @@ int Query::NextSolution()
 }
 
 /* Convert Prolog term to wide characters. */
-int PlString(const term_t t, std::wstring* const pWs, const int iFlags)
+wstring_owner PlString(const term_t t, const int iFlags)
 {
 	char* sz;
-	int r = PL_get_chars(t, &sz, iFlags);
-	if (r) *pWs = WsFromSz(sz);
-	return r;
+	if (PL_get_chars(t, &sz, iFlags))
+		return {WsoFromSz(sz)};
+	else
+		return {};
 }
diff --git a/c/pl.h b/c/pl.h
index c0af4bc..c7fcfc8 100644
--- a/c/pl.h
+++ b/c/pl.h
@@ -7,7 +7,7 @@
 
 #include "common.h"
 
-int PlString(term_t t, std::wstring* pWs, int iFlags = CVT_WRITE);
+wstring_owner PlString(const term_t t, const int iFlags = CVT_WRITE);
 
 struct Frame
 {
@@ -54,8 +54,7 @@ inline int PlPut(term_t, long*) { return -1; }
 inline int PlPut(term_t, long long*) { return -1; }
 inline int PlPut(term_t, atom_t*) { return -1; }
 inline int PlPut(term_t, char**) { return -1; }
-inline int PlPut(term_t, std::string*) { return -1; }
-inline int PlPut(term_t, std::wstring*) { return -1; }
+inline int PlPut(term_t, wstring_owner*) { return -1; }
 
 inline int PlGet(term_t, int) { return -1; }
 inline int PlGet(term_t, long) { return -1; }
@@ -68,18 +67,11 @@ inline int PlGet(term_t t, long* x) { return PL_get_long(t, x); }
 inline int PlGet(term_t t, long long* x) { return PL_get_int64(t, x); }
 inline int PlGet(term_t t, atom_t* x) { return PL_get_atom(t, x); }
 inline int PlGet(term_t t, char** x) { return PL_get_atom_chars(t, x); }
-inline int PlGet(term_t t, std::string* x) { 
+inline int PlGet(term_t t, wstring_owner* x) {
 	Mark m;
 	char* sz;
 	if (!PlGet(t, &sz)) return 0;
-	*x = sz;
-	return 1;
-}
-inline int PlGet(term_t t, std::wstring* x) { 
-	Mark m;
-	char* sz;
-	if (!PlGet(t, &sz)) return 0;
-	*x = WsFromSz(sz);
+	*x = WsoFromSz(sz);
 	return 1; /* or catch potential exception from BstrFromSz? */
 }