From 0d5736538a98b2c4001c45d073affc6bc0d772e5 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?John=20Ankarstr=C3=B6m?= <john@ankarstrom.se>
Date: Wed, 20 Jul 2022 20:15:22 +0200
Subject: Use GetLastError() as default for Win32Error.

---
 README       |  4 ++++
 c/common.cpp |  3 ++-
 c/common.h   | 15 ++++++++-------
 3 files changed, 14 insertions(+), 8 deletions(-)

diff --git a/README b/README
index 77e46d6..ebe22ef 100644
--- a/README
+++ b/README
@@ -76,6 +76,10 @@ Following is a summary of some coding conventions used in the project.
  - wstr	= ... (std::wstring)
  - tstr	= ... (std::basic_string<TCHAR>)
 
+The list above is non-exhaustive. Variables whose type is unknown (in
+templates) do not need prefixes. Some very common self-explanatory
+variables also do not need prefixes, e.g. len (usually size_t).
+
 			    ... TYPES ...
 
 Here are some general guidelines for choosing what types to use:
diff --git a/c/common.cpp b/c/common.cpp
index ba52f2c..25ff899 100644
--- a/c/common.cpp
+++ b/c/common.cpp
@@ -4,6 +4,7 @@
 
 /* Win32Error: Exception for Windows API errors. */
 
+Win32Error::Win32Error() : m_dwErr(GetLastError()) {}
 Win32Error::Win32Error(const DWORD dwErr) : m_dwErr(dwErr) {}
 
 Win32Error::~Win32Error()
@@ -48,7 +49,7 @@ Library::Library(const TCHAR* const tszLibrary)
 {
 	m_hModule = LoadLibrary(tszLibrary);
 	if (!m_hModule)
-		throw Win32Error(GetLastError());
+		throw Win32Error();
 }
 
 Library::~Library()
diff --git a/c/common.h b/c/common.h
index d84590d..24c98c8 100644
--- a/c/common.h
+++ b/c/common.h
@@ -15,6 +15,7 @@ int EBMessageBox(const TCHAR* tszText, const TCHAR* tszCaption, unsigned uType);
 
 struct Win32Error : public std::exception
 {
+	Win32Error();
 	Win32Error(DWORD dwErr);
 	~Win32Error();
 	template <typename T = char> const T* what() const noexcept;
@@ -57,19 +58,19 @@ std::optional<T> maybe_make(U... xs)
 template <auto F, typename... T>
 inline auto require(T... xs)
 {
-	auto r = F(xs...);
-	if (!r) throw Win32Error(GetLastError());
-	return r;
+	if (auto r = F(xs...)) return r;
+	else throw Win32Error();
 }
 
 /* Call Windows API function, showing a warning on NULL. */
 template <auto F, typename... T>
 inline auto prefer(T... xs)
 {
-	try {
-		return require<F>(xs...);
-	} catch (Win32Error& e) {
-		EBMessageBox(e.what<TCHAR>(), TEXT("System Error"), MB_ICONWARNING);
+	if (auto r = F(xs...))
+		return r;
+	else {
+		EBMessageBox(Win32Error().what<TCHAR>(),
+			TEXT("System Error"), MB_ICONWARNING);
 		return (decltype(F(std::declval<T>()...)))NULL;
 	}
 }
-- 
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