Re: [Boost-users] Serialization--a peculiar observation regardingoperator<<

From: Oliver Mutz (mutz_at_[hidden])
Date: 2006-04-03 04:39:28

Try changing the return type of foo() to const double.
For the reason see the ratinale page in the serialization documentation.

Oliver

Drumheller, Michael wrote:
> The test program below (under boost 1_33, vc71) compiles fine, unless
> I change the "#if 1" to "#if 0", in which case it produces this:
> error C2679: binary '<<': no operator found which takes a right-hand
> operand of type 'double' (or there is no acceptable conversion)   
> 
> Can anyone explain why that should happen?  A double is a double--why
> should '<<' care whether the rhs comes from funcall a variable? 
> 
> Note:  The test program is clearly a nonsense program (in real life
> the role of foo() is played by some public (get-accessor) on klass--a
> very common pattern when doing a non-intrusive serialization).  But I
> did not want to cloud the issue--I wanted to emphasize that the bug,
> if it is a bug, seems to have nothing to with klass.    
> 
> Thank you.
> 
> Michael Drumheller
> -----------------------------------------------------------------begin--
> -------------------------------------------------------------
> 	#include <fstream>
> 	#include <boost/archive/text_oarchive.hpp>
> 	#include <boost/serialization/split_free.hpp>
> 	class klass {};
> 	double foo() { return 3.1416; }
> 	namespace boost { namespace serialization {
> 	  template<class Archive>
> 	  void save(Archive &ar, const klass & b, const unsigned int
> ver)
> 	  {
> 	#if 1
> 	    double x=foo();
> 	    ar << x;
> 	#else
> 	    ar << foo();
> 	#endif
> 	  }
> 	  template<class Archive>
> 	  void load(Archive &ar, klass & b, const unsigned int ver){}//N/A
> 	for this demo }}
> 	BOOST_SERIALIZATION_SPLIT_FREE(klass);
> 	void out(const char *testfile, const klass & c)
> 	{
> 	  std::ofstream ofs(testfile);
> 	  boost::archive::text_oarchive oa(ofs);
> 	  oa << c;
> 	}
> ----------------------------------------------------------------end-----
> -----------------------------------------------------------------
> Michael Drumheller
> Boeing Phantom Works
> Mathematics and Engineering Analysis
> 425.865.3520 michael.drumheller_at_[hidden]
> 
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