Added to trunk

[SVN r70067]

example/doc_file_descriptor.cpp

@@ -0,0 +1,87 @@
+//////////////////////////////////////////////////////////////////////////////
+//
+// (C) Copyright Ion Gaztanaga 2008-2009.
+// 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)
+//
+// See http://www.boost.org/libs/move for documentation.
+//
+//////////////////////////////////////////////////////////////////////////////
+
+//[file_descriptor_def
+
+#include <boost/move/move.hpp>
+#include <stdexcept>
+
+class file_descriptor
+{
+   //<-
+   int operating_system_open_file(const char *)
+   {
+      return 1;
+   }
+
+   void operating_system_close_file(int)
+   {}
+   //->
+   int os_descr_;
+
+   private:
+   BOOST_MOVABLE_BUT_NOT_COPYABLE(file_descriptor)
+
+   public:
+   explicit file_descriptor(const char *filename = 0)          //Constructor
+      : os_descr_(filename ? operating_system_open_file(filename) : 0)
+   {  if(!os_descr_) throw std::runtime_error("file not found");  }
+
+   ~file_descriptor()                                          //Destructor
+   {  if(!os_descr_)  operating_system_close_file(os_descr_);  }
+
+   file_descriptor(BOOST_RV_REF(file_descriptor) x)            // Move ctor
+      :  os_descr_(x.os_descr_)
+   {  x.os_descr_ = 0;  }      
+
+   file_descriptor& operator=(BOOST_RV_REF(file_descriptor) x) // Move assign
+   {
+      if(!os_descr_) operating_system_close_file(os_descr_);
+      os_descr_   = x.os_descr_;
+      x.os_descr_ = 0;
+      return *this;
+   }
+
+   bool empty() const   {  return os_descr_ == 0;  }
+};
+
+//]
+
+//[file_descriptor_example
+#include <boost/interprocess/containers/vector.hpp>
+#include <cassert>
+
+//Remember: 'file_descriptor' is NOT copyable, but it
+//can be returned from functions thanks to move semantics
+file_descriptor create_file_descriptor(const char *filename)
+{  return file_descriptor(filename);  }
+
+int main()
+{
+   //Open a file obtaining its descriptor, the temporary
+   //returned from 'create_file_descriptor' is moved to 'fd'.
+   file_descriptor fd = create_file_descriptor("filename");
+   assert(!fd.empty());
+
+   //Now move fd into a vector
+   boost::interprocess::vector<file_descriptor> v;
+   v.push_back(boost::move(fd));
+
+   //Check ownership has been transferred
+   assert(fd.empty());
+   assert(!v[0].empty());
+
+   //Compilation error if uncommented since file_descriptor is not copyable
+   //and vector copy construction requires value_type's copy constructor:
+   //boost::interprocess::vector<file_descriptor> v2(v);
+   return 0;
+}
+//]