Bring into compliance with N2066, TR2 Diagnostics Enhancements. Tests passing on Win32, Linux, on most modern compilers.

[SVN r35823]

include/boost/system/system_error.hpp

@@ -0,0 +1,78 @@
+//  Boost system_error.hpp  --------------------------------------------------//
+
+//  Copyright Beman Dawes 2006
+
+//  Distributed under the Boost Software License, Version 1.0. (See accompanying
+//  file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#ifndef BOOST_SYSTEM_ERROR_HPP
+#define BOOST_SYSTEM_ERROR_HPP
+
+#include <string>
+#include <stdexcept>
+#include <cassert>
+#include <boost/system/error_code.hpp>
+
+namespace boost
+{
+  namespace system
+  {
+    enum message_action { append_message, no_message };
+    
+    //  class system_error  --------------------------------------------------//
+
+    class system_error : public std::runtime_error
+    {
+    public:
+      explicit system_error( error_code ec )
+        : std::runtime_error(std::string()), m_error_code(ec),
+          m_append_message(true) {}
+
+      system_error( error_code ec, const std::string & what_arg,
+        message_action ma = append_message )
+          : std::runtime_error(what_arg), m_error_code(ec),
+            m_append_message(ma==append_message) {}
+
+      system_error( error_code::value_type ev, error_category ecat )
+        : std::runtime_error(std::string()), m_error_code(ev,ecat),
+          m_append_message(true) {}
+
+      system_error( error_code::value_type ev, error_category ecat,
+        const std::string & what_arg, message_action ma = append_message )
+          : std::runtime_error(what_arg), m_error_code(ev,ecat),
+            m_append_message(ma==append_message) {}
+
+      virtual ~system_error() throw() {}
+
+      const error_code & code() const throw() { return m_error_code; }
+
+      const char * what() const throw()
+      // see http://www.boost.org/more/error_handling.html for lazy build rationale
+      {
+        if ( !m_error_code || !m_append_message ) return runtime_error::what();
+        if ( m_what.empty() )
+        {
+          try
+          {
+            m_what = runtime_error::what();
+            if ( !m_what.empty() ) m_what += ": ";
+            m_what += m_error_code.message();
+          }
+          catch (...) { return runtime_error::what(); }
+        }
+        return m_what.c_str();
+      }
+
+
+    private:
+      error_code           m_error_code;
+      mutable std::string  m_what;
+      bool                 m_append_message;
+    };
+
+  } // namespace system
+} // namespace boost
+
+#endif // BOOST_SYSTEM_ERROR_HPP
+
+