new attribute for a columns view: do not display empty tag marker

doc/config

@@ -131,9 +131,13 @@
 ##
 ## - color is optional (if you want the default one, type [])
 ##
-## Note: If you want a column to be right aligned, put 'r' character
-## after displayed tag character, e.g. {lr} will give you right aligned
-## column of lengths.
+## Note: You can give a column additional attributes by putting appropriate
+## character after displayed tag character. Available attributes are:
+##
+## - r - column will be right aligned
+## - E - if tag is empty, empty tag marker won't be displayed
+##
+## E.g. {lr} will give you right aligned column of lengths.
 ##
 #
 #song_columns_list_format = "(7f)[green]{l} (25)[cyan]{a} (40)[]{t} (30)[red]{b}"

src/display.cpp

@@ -181,16 +181,19 @@ void Display::SongsInColumns(const MPD::Song &s, void *, Menu<MPD::Song> *menu)
 		std::string tag = (s.*get)();
 		if (it->right_alignment)
 		{
-			int x, y;
-			menu->GetXY(x, y);
-			std::basic_string<my_char_t> wtag = TO_WSTRING(tag.empty() ? Config.empty_tag : tag).substr(0, width-!!x);
-			*menu << XY(x+width-Window::Length(wtag)-!!x, y) << wtag;
+			if (!tag.empty() || it->display_empty_tag)
+			{
+				int x, y;
+				menu->GetXY(x, y);
+				std::basic_string<my_char_t> wtag = TO_WSTRING(tag.empty() ? Config.empty_tag : tag).substr(0, width-!!x);
+				*menu << XY(x+width-Window::Length(wtag)-!!x, y) << wtag;
+			}
 		}
 		else
 		{
 			if (!tag.empty())
 				*menu << tag;
-			else
+			else if (it->display_empty_tag)
 				*menu << Config.empty_tag;
 		}
 		where += width;

src/settings.cpp

@@ -881,7 +881,18 @@ void ReadConfiguration(ncmpcpp_config &conf)
 		std::string tag_type = GetLineValue(conf.song_list_columns_format, '{', '}', 1);
 		col.type = tag_type.at(0);
 		col.fixed = *width.rbegin() == 'f';
-		col.right_alignment = tag_type.length() > 1 && tag_type[1] == 'r';
+		for (std::string::const_iterator it = ++tag_type.begin(); it != tag_type.end(); ++it)
+		{
+			switch (*it)
+			{
+				case 'r':
+					col.right_alignment = 1;
+					break;
+				case 'E':
+					col.display_empty_tag = 0;
+					break;
+			}
+		}
 		col.width = StrToInt(width);
 		conf.columns.push_back(col);
 	}

src/settings.h

@@ -39,11 +39,14 @@ const int null_key = std::numeric_limits<int>::max();
 
 struct Column
 {
+	Column() : right_alignment(0), display_empty_tag(1) { }
+	
 	unsigned width;
 	Color color;
 	char type;
 	bool fixed;
 	bool right_alignment;
+	bool display_empty_tag;
 };
 
 struct ncmpcpp_keys