Added function to create an empty archive

2 files changed, 32 insertions, 0 deletions

diff --git a/ArchiveEx/Archive.cpp b/ArchiveEx/Archive.cpp
index 4275502..e5f2c8f 100644
--- a/ArchiveEx/Archive.cpp
+++ b/ArchiveEx/Archive.cpp
@@ -26,6 +26,35 @@ static constexpr int UNUSED_BLOCK {-1};
 static constexpr int DIRECTORY_BLOCK {-2};
 
 
+Archive
+CreateEmpty(const char* path)
+{
+	Header header = {VERSION, 0, {0, 0, 0}};
+	std::vector<Entry> entries;
+	entries.reserve(DIRECTORY_MARGIN);
+	const std::size_t uncompressed_size = DIRECTORY_MARGIN * sizeof(Entry);
+	uLongf compressed_size = uncompressed_size * 1.1 + 12;
+	auto compressed = std::make_unique<Bytef[]>(compressed_size);
+	int err = compress(
+		compressed.get(),
+		&compressed_size,
+		reinterpret_cast<Bytef*>(entries.data()),
+		uncompressed_size);
+	if (Z_OK != err)
+		throw "could not compress directory metadata";
+	header.directory.compressed_size = compressed_size;
+	UniqueFileHandle archive {std::fopen(path, "wb"), &std::fclose};
+	err = std::fwrite(&header, sizeof(Header), 1, archive.get());
+	if (1 != err)
+		throw "could not write header (write)";
+	err = std::fwrite(compressed.get(), 1, compressed_size, archive.get());
+	if (static_cast<int>(compressed_size) != err)
+		throw "could not write directory (write)";
+	archive.reset();
+	return Archive(path);
+}
+
+
 Archive::Archive(const char* p) :
 	path {p},
 	header {},
diff --git a/ArchiveEx/Archive.h b/ArchiveEx/Archive.h
index ed042f6..64b73d5 100644
--- a/ArchiveEx/Archive.h
+++ b/ArchiveEx/Archive.h
@@ -55,4 +55,7 @@ private:
 };
 
 
+Archive CreateEmpty(const char* path);
+
+
 }  // namespace Archive