Index: boost/format/format_class.hpp
===================================================================
--- boost/format/format_class.hpp	(revision 51826)
+++ boost/format/format_class.hpp	(working copy)
@@ -50,12 +50,22 @@
 #endif
         io::detail::locale_t  getloc() const;
 
+        // The total number of arguments expected to be passed to the format 
string.
+        int expected_args() const
+            { return num_args_; }
+        // The number of arguments currently bound to the format string.
+        int bound_args() const
+            { return cur_arg_; }
+        // The number of arguments still required to be passed to the format 
string.
+        int remaining_args() const
+            { return expected_args() - bound_args(); }
+
         basic_format& clear();       // empty all converted string buffers 
(except bound items)
         basic_format& clear_binds(); // unbind all bound items, and call 
clear()
         basic_format& parse(const string_type&); // resets buffers and parse a 
new format string
 
         // ** formatted result ** //
-        size_type   size() const;    // sum of the current string pieces sizes
+        size_type   size() const;    // The number of characters in the 
formatted result string.
         string_type str()  const;    // final string 
 
         // ** arguments passing ** //
@@ -127,7 +137,7 @@
         std::vector<format_item_t>  items_; // each '%..' directive leads to a 
format_item
         std::vector<bool> bound_; // stores which arguments were bound. size() 
== 0 || num_args
 
-        int              style_; // style of format-string :  positional or 
not, etc
+        int               style_; // style of format-string :  positional or 
not, etc
         int             cur_arg_; // keep track of wich argument is current
         int            num_args_; // number of expected arguments
         mutable bool     dumped_; // true only after call to str() or <<
Index: libs/format/test/format_test3.cpp
===================================================================
--- libs/format/test/format_test3.cpp	(revision 51826)
+++ libs/format/test/format_test3.cpp	(working copy)
@@ -93,6 +93,31 @@
       BOOST_ERROR("nesting did not work");
     }
 
+    // observers
+    BOOST_CHECK_EQUAL(format("foo").expected_args(), 0);
+    BOOST_CHECK_EQUAL(format("foo").bound_args(), 0);
+    BOOST_CHECK_EQUAL(format("foo").remaining_args(), 0);
+
+    BOOST_CHECK_EQUAL(format("foo%s").expected_args(), 1);
+    BOOST_CHECK_EQUAL(format("foo%s").bound_args(), 0);
+    BOOST_CHECK_EQUAL(format("foo%s").remaining_args(), 1);
+
+    BOOST_CHECK_EQUAL((format("foo%s") % "bar").expected_args(), 1);
+    BOOST_CHECK_EQUAL((format("foo%s") % "bar").bound_args(), 1);
+    BOOST_CHECK_EQUAL((format("foo%s") % "bar").remaining_args(), 0);
+
+    BOOST_CHECK_EQUAL((format("%2%%1%") % "bar" % "foo").expected_args(), 
2);
+    BOOST_CHECK_EQUAL((format("%2%%1%") % "bar" % "foo").bound_args(), 2);
+    BOOST_CHECK_EQUAL((format("%2%%1%") % "bar" % "foo").remaining_args(), 
0);
+
+    BOOST_CHECK_EQUAL((format("%1$s %2$s %1$s") % "bar").expected_args(), 
2);
+    BOOST_CHECK_EQUAL((format("%1$s %2$s %1$s") % "bar").bound_args(), 1);
+    BOOST_CHECK_EQUAL((format("%1$s %2$s %1$s") % "bar").remaining_args(), 
1);
+
+    BOOST_CHECK_EQUAL((format("%1%, %2%, %|40t|%3%\n") % "foo" % 
"bar").expected_args(), 3);
+    BOOST_CHECK_EQUAL((format("%1%, %2%, %|40t|%3%\n") % "foo" % 
"bar").bound_args(), 2);
+    BOOST_CHECK_EQUAL((format("%1%, %2%, %|40t|%3%\n") % "foo" % 
"bar").remaining_args(), 1);
+
     // testcase for bug reported at 
     // http://lists.boost.org/boost-users/2006/05/19723.php
     format f("%40t%1%");