Added select_oldest_file() and select_newest_file()

dlib/dir_nav/dir_nav_extensions.cpp

@@ -77,6 +77,40 @@ namespace dlib
         return directory(f.full_name().substr(0,pos));
     }
 
+// ----------------------------------------------------------------------------------------
+
+    std::string select_oldest_file (
+        const std::string& filename1,
+        const std::string& filename2
+    )
+    {
+        file f1, f2;
+        try{f1 = file(filename1);} catch(file::file_not_found&) { return filename1; }
+        try{f2 = file(filename2);} catch(file::file_not_found&) { return filename2; }
+
+        if (f1.last_modified() < f2.last_modified())
+            return filename1;
+        else
+            return filename2;
+    }
+
+// ----------------------------------------------------------------------------------------
+
+    std::string select_newest_file (
+        const std::string& filename1,
+        const std::string& filename2
+    )
+    {
+        file f1, f2;
+        try{f1 = file(filename1);} catch(file::file_not_found&) { return filename2; }
+        try{f2 = file(filename2);} catch(file::file_not_found&) { return filename1; }
+
+        if (f1.last_modified() > f2.last_modified())
+            return filename1;
+        else
+            return filename2;
+    }
+
 // ----------------------------------------------------------------------------------------
 
 }

dlib/dir_nav/dir_nav_extensions.h

@@ -146,6 +146,20 @@ namespace dlib
         const file& f
     );
 
+// ----------------------------------------------------------------------------------------
+
+    std::string select_oldest_file (
+        const std::string& filename1,
+        const std::string& filename2
+    );
+
+// ----------------------------------------------------------------------------------------
+
+    std::string select_newest_file (
+        const std::string& filename1,
+        const std::string& filename2
+    );
+
 // ----------------------------------------------------------------------------------------
 
 }

dlib/dir_nav/dir_nav_extensions_abstract.h

@@ -165,6 +165,35 @@ namespace dlib
                 - returns a default initialized directory (i.e. directory())
     !*/
 
+// ----------------------------------------------------------------------------------------
+
+    std::string select_oldest_file (
+        const std::string& filename1,
+        const std::string& filename2
+    );
+    /*!
+        ensures
+            - Checks the last modification times of the two given files and returns the
+              filename of the oldest file, i.e., the file that has gone longest since being
+              modified.  Ties are broken arbitrarily. 
+            - For the purpose of comparison, a file that doesn't exist is presumed to have
+              a last modification time of -infinity (i.e. very far in the past).
+    !*/
+
+// ----------------------------------------------------------------------------------------
+
+    std::string select_newest_file (
+        const std::string& filename1,
+        const std::string& filename2
+    );
+    /*!
+        ensures
+            - Checks the last modification times of the two given files and returns the
+              filename that was most recently modified.  Ties are broken arbitrarily. 
+            - For the purpose of comparison, a file that doesn't exist is presumed to have
+              a last modification time of -infinity (i.e. very far in the past).
+    !*/
+
 // ----------------------------------------------------------------------------------------
 
 }