step 2

apps/LoopThroughWithOpenGLCompositing/runtime/persistence/PersistenceWriter.cpp

@@ -0,0 +1,44 @@
+#include "PersistenceWriter.h"
+
+#include <windows.h>
+
+#include <filesystem>
+#include <fstream>
+
+bool PersistenceWriter::WriteSnapshot(const PersistenceSnapshot& snapshot, std::string& error) const
+{
+	if (snapshot.targetPath.empty())
+	{
+		error = "Persistence snapshot target path is empty.";
+		return false;
+	}
+
+	std::error_code fsError;
+	std::filesystem::create_directories(snapshot.targetPath.parent_path(), fsError);
+
+	const std::filesystem::path temporaryPath = snapshot.targetPath.string() + ".tmp";
+	std::ofstream output(temporaryPath, std::ios::binary | std::ios::trunc);
+	if (!output)
+	{
+		error = "Could not write file: " + temporaryPath.string();
+		return false;
+	}
+
+	output << snapshot.contents;
+	output.close();
+	if (!output.good())
+	{
+		error = "Could not finish writing file: " + temporaryPath.string();
+		return false;
+	}
+
+	if (!MoveFileExA(temporaryPath.string().c_str(), snapshot.targetPath.string().c_str(), MOVEFILE_REPLACE_EXISTING | MOVEFILE_WRITE_THROUGH))
+	{
+		const DWORD lastError = GetLastError();
+		std::filesystem::remove(temporaryPath, fsError);
+		error = "Could not replace file: " + snapshot.targetPath.string() + " (Win32 error " + std::to_string(lastError) + ")";
+		return false;
+	}
+
+	return true;
+}

apps/LoopThroughWithOpenGLCompositing/runtime/persistence/PersistenceWriter.h

@@ -0,0 +1,11 @@
+#pragma once
+
+#include "PersistenceRequest.h"
+
+#include <string>
+
+class PersistenceWriter
+{
+public:
+	bool WriteSnapshot(const PersistenceSnapshot& snapshot, std::string& error) const;
+};