Improve error reporting.

The name of option is now shown in most cases when it's feasible, and
clarify of the error messages has been improved throughout.

Patch from Leo Goodstadt.


[SVN r77827]

Author: vprus

example/first.cpp

@@ -20,7 +20,7 @@ int main(int ac, char* av[])
         po::options_description desc("Allowed options");
         desc.add_options()
             ("help", "produce help message")
-            ("compression", po::value<int>(), "set compression level")
+            ("compression", po::value<double>(), "set compression level")
         ;
 
         po::variables_map vm;        
@@ -34,7 +34,7 @@ int main(int ac, char* av[])
 
         if (vm.count("compression")) {
             cout << "Compression level was set to " 
-                 << vm["compression"].as<int>() << ".\n";
+                 << vm["compression"].as<double>() << ".\n";
         } else {
             cout << "Compression level was not set.\n";
         }

include/boost/program_options/detail/cmdline.hpp

@@ -81,6 +81,18 @@ namespace boost { namespace program_options { namespace detail {
         cmdline(int argc, const char*const * argv);
 
         void style(int style);
+
+        /** returns the canonical option prefix associated with the command_line_style
+         *  In order of precedence:
+         *      allow_long           : allow_long
+         *      allow_long_disguise  : allow_long_disguise
+         *      allow_dash_for_short : allow_short | allow_dash_for_short
+         *      allow_slash_for_short: allow_short | allow_slash_for_short
+         *  
+         *      This is mainly used for the diagnostic messages in exceptions
+        */ 
+        int         get_canonical_option_prefix();
+
         void allow_unregistered();
 
         void set_options_description(const options_description& desc);

include/boost/program_options/detail/parsers.hpp

@@ -100,7 +100,11 @@ namespace boost { namespace program_options {
     basic_parsed_options<charT>
     basic_command_line_parser<charT>::run()
     {
-        parsed_options result(m_desc);
+        // save the canonical prefixes which were used by this cmdline parser
+        //    eventually inside the parsed results
+        //    This will be handy to format recognisable options
+        //    for diagnostic messages if everything blows up much later on
+        parsed_options result(m_desc, detail::cmdline::get_canonical_option_prefix());
         result.options = detail::cmdline::run();
 
         // Presense of parsed_options -> wparsed_options conversion