Re: [Boost-users] [Boost.Serialization] How to make CString behave likea primitive in xml archive?

19 Oct 2006

      Robert Ramey  writes:
...
Markus Werle wrote:
...
Robert Ramey  writes:
...
...
The easiest would be just to define non-untrusive serialize
templates for these classes.
Unfortunately this approach still requires an extra nvp for xml
files, so for the code below we obtain e.g.
<SomeTag><value>SomeText</value><SomeTag>
The extra tag is what I would like to avoid.
Note that usage of std::string rather than CString will
have the same "extra" tag.
I disagree. Probably I did not explain my intention/problem precise enough.
To store a std::string in an xml file you need 1 tag, not 2 like for CString.
You store it by using 

std::string myStdString = "Test";
[...]
ar & make_nvp("SomeTag", myStdString);

and obtain an xml file with a line

<SomeTag>Test<SomeTag>

which is exactly what I want. But now I want this for any
type which has a string representation, e.g. CString from MFC
(the lib I hate most)

As I showed in a previous post the classical approach, which you 
also mention in modified form bails out due to missing _extra_ nvp!
Compiler fails on 

template<class Archive>
inline void save(Archive & ar,
		CString const & S,
		unsigned int const /* file_version */)
{
	using boost::serialization::make_nvp;
	std::string const s(S);

	ar << s; 
}
with [...]basic_xml_oarchive.hpp(86) : error C2027: use of undefined type
'boost::STATIC_ASSERTION_FAILURE<> etc.

even if you store the CString using an nvp like in

CString myStdString = "Test";
[...]
ar & make_nvp("SomeTag", myStdString);

So there is an unnecessary (?) asymmetry between CString and std::string.
...
what's the matter with adding to MyType a common string cast operator
and using:
template<class Archive>
void save(Archive &ar, const MyType &t, const unsigned version){
    std::string s = t;
    ar << t;
}
 and
std::ostream & operator<<(std::ostream &os, MyType const & T){
    std::string s = t;
    *this << t;
}
This is what I tried with CString. My approach yields an xml file
with a line containing 
<SomeTag><value>Test</value><SomeTag>

using

template<class Archive>
inline void save(Archive & ar,
		 CString const & S,
	 unsigned int const /* file_version */)
{
	using boost::serialization::make_nvp;
	std::string const s(S);

	ar << make_nvp("value", s); 
}

I still cannot see how to avoid this extra <value> tag. 
Did it become clear now?

Markus