--- C:/Users/Paul/AppData/Local/Temp/io.hpp-revBASE.svn002.tmp.hpp	Thu Mar 31 19:28:33 2011
+++ I:/boost-trunk/boost/units/io.hpp	Wed Aug 22 17:25:54 2012
@@ -1041,22 +1041,34 @@
 template<class Char, class Traits, class Unit, class T>
 inline std::basic_ostream<Char, Traits>& operator<<(std::basic_ostream<Char, Traits>& os, const quantity<Unit, T>& q)
 {
+    std::ostringstream oss;
+    // if os.width() > 0 then need to build a single string of the quantity
+    // with the width specified using ostringstream
+    // (otherwise, outputing value and unit (perhaps autoprefixed to km)
+    // severally would overflow the width).
+    // else output directly to ostream os.
+
     if (units::get_autoprefix(os) == autoprefix_none)
     {
-        os << q.value() << ' ' << Unit();
+      ((os.width()> 0) ? oss : os) << q.value() << ' ' << Unit();
     }
     else if (units::get_autoprefix(os) == autoprefix_engineering)
     {
-        detail::maybe_print_prefixed<detail::engineering_prefixes>(os, q, detail::test_norm(autoprefix_norm(q.value())));
+        detail::maybe_print_prefixed<detail::engineering_prefixes>(((os.width() > 0) ? oss : os), q, detail::test_norm(autoprefix_norm(q.value())));
     }
     else if (units::get_autoprefix(os) == autoprefix_binary)
     {
-        detail::maybe_print_prefixed<detail::binary_prefixes>(os, q, detail::test_norm(autoprefix_norm(q.value())));
+        detail::maybe_print_prefixed<detail::binary_prefixes>(((os.width() > 0) ? oss : os), q, detail::test_norm(autoprefix_norm(q.value())));
     }
     else
     {
         assert(!"Autoprefixing must be one of: no_prefix, engineering_prefix, binary_prefix");
     }
+    if (os.width() > 0)
+    {
+      os << oss.str();  // Would be "" string if oss not used.
+    }
+
     return(os);
 }