Use GetLastError() as default for Win32Error.

1 files changed, 8 insertions, 7 deletions

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;
 	}
 }