+ /// Method to check if a file is externally modified, used by
+ /// isExternallyModified()
+ /**
+ * timestamp is fast but inaccurate. For example, the granularity
+ * of timestamp on a FAT filesystem is 2 second. Also, various operations
+ * may touch the timestamp of a file even when its content is unchanged.
+ *
+ * checksum is accurate but slow, which can be a problem when it is
+ * frequently used, or used for a large file on a slow (network) file
+ * system.
+ */
+ enum CheckMethod {
+ checksum_method, ///< Use file check sum
+ timestamp_method, ///< Use timestamp, and checksum if timestamp has changed
+ };
+