3 files changed, 35 insertions, 0 deletions
diff --git a/include/cru/common/io/CFileStream.h b/include/cru/common/io/CFileStream.h
index 65de2ac7..5d464c9b 100644
--- a/include/cru/common/io/CFileStream.h
+++ b/include/cru/common/io/CFileStream.h
@@ -1,6 +1,7 @@
 #pragma once
 
 #include "Stream.h"
+#include "OpenFileFlag.h"
 
 #include <cstdio>
 
@@ -11,6 +12,8 @@ class CRU_BASE_API CFileStream : public Stream {
   explicit CFileStream(std::FILE* file, bool readable = true,
                        bool writable = true, bool auto_close = true);
 
+  CFileStream(String path, OpenFileFlag flags); // To make it a FileStream
+
   CRU_DELETE_COPY(CFileStream)
   CRU_DELETE_MOVE(CFileStream)
 
diff --git a/include/cru/common/io/FileStream.h b/include/cru/common/io/FileStream.h
index 9176739a..4eab612f 100644
--- a/include/cru/common/io/FileStream.h
+++ b/include/cru/common/io/FileStream.h
@@ -17,6 +17,11 @@
  * (TODO: Currently the problem is that when I implemented for Windows and UNIX
  * I didn't take this into consideration so I have to fix this inconsistency
  * later.)
+ *
+ * The requirement of FileStream:
+ * 1. It must be derived from Stream, of course.
+ * 2. It must have a constructor FileStream(String path, io::OpenFlag flags), so
+ * user can construct one with the same interface.
  */
 
 #pragma once
diff --git a/include/cru/common/io/OpenFileFlag.h b/include/cru/common/io/OpenFileFlag.h
index bca1d737..fd8b6e2c 100644
--- a/include/cru/common/io/OpenFileFlag.h
+++ b/include/cru/common/io/OpenFileFlag.h
@@ -9,11 +9,38 @@ struct OpenFileFlagTag {};
 using OpenFileFlag = Bitmask<details::OpenFileFlagTag>;
 
 struct OpenFileFlags {
+  /**
+   * \brief for reading
+   */
   static constexpr OpenFileFlag Read{0x1};
+
+  /**
+   * \brief for writing
+   */
   static constexpr OpenFileFlag Write{0x2};
+
+  /**
+   * \brief when writing, seek to end first
+   * Only effective for writing.
+   */
   static constexpr OpenFileFlag Append{0x4};
+
+  /**
+   * \brief when writing, truncate the file to empty
+   * Only effective for writing.
+   * So the content is erased! Be careful!
+   */
   static constexpr OpenFileFlag Truncate{0x8};
+
+  /**
+   * \brief when writing, if the file does not exist, create one
+   * Only effective for writing.
+   */
   static constexpr OpenFileFlag Create{0x10};
+
+  /**
+   *  TODO: ???
+   */
   static constexpr OpenFileFlag Exclusive{0x20};
 };
 }  // namespace cru::io