Check Windows API calls for errors more consistently.

Some of the checks are likely redundant, but the Windows API
documentation rarely makes it clear WHICH errors may be returned (and
under which circumstances) rather than simply WHETHER errors may be
returned (under any circumstances, including those that do not apply
in the given case).

1 files changed, 23 insertions, 1 deletions

diff --git a/c/common.h b/c/common.h
index bffc9e5..acb8f26 100644
--- a/c/common.h
+++ b/c/common.h
@@ -44,7 +44,7 @@ T* Library::GetProcAddress(const char* const szProc)
  * return nothing. The returned value must be checked before being
  * used, as dereferencing is undefined if the value is empty. */
 template <class C, typename ...T>
-std::optional<C> try_make(T ...args)
+std::optional<C> maybe_make(T ...args)
 {
 	try {
 		return C(args...);
@@ -53,6 +53,28 @@ std::optional<C> try_make(T ...args)
 	}
 }
 
+/* Call Windows API function and throw error if NULL is returned. */
+template <auto f, typename ...T>
+inline auto throw_nil(T ...args)
+{
+	auto r = f(args...);
+	if (!r) throw Win32Error(GetLastError());
+	return r;
+}
+
+/* Call Windows API function and show a warning if NULL is returned. */
+template <auto f, typename ...T>
+inline auto warn_nil(T ...args)
+{
+	decltype(f(args...)) r;
+	try {
+		r = throw_nil<f>(args...);
+	} catch (Win32Error& e) {
+		EBMessageBox(e.twhat(), TEXT("System Error"), MB_ICONWARNING);
+	}
+	return r;
+}
+
 /* Return integer scaled for current DPI. */
 inline int Dpi(const int i)
 {