Serialization of optional<std::string>

Chardrazle

19 Feb 2018 19 Feb '18

12:35 p.m.

As part of upgrading a product to a later version of boost the compilation has tripped up on serialization of a boost::optionalstd::string. The /optional.hpp/ header now has the comment: ...and this fires for std::string. What, if any, is the recommended way forward for this? An example code snippet to illustrate: Previous version of boost: 1.50; new: 1.6x Compiling with g++ 4.6.4 (although same problem with 4.8.5): -W -Wall -std=c++0x... (The real code is actually using the portable_binary_archive, but let's avoid muddying the waters at this stage :) -- Sent from: http://boost.2283326.n4.nabble.com/Boost-Users-f2553780.html

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Chardrazle

19 Feb 19 Feb

12:41 p.m.

OK, so it looks like posting from nabble loses the raw-tag stuff... The optional.hpp comment: // It is an inherent limitation to the serialization of optional.hpp // that the underlying type must be either a pointer or must have a // default constructor. It's possible that this could change sometime // in the future, but for now, one will have to work around it. This can // be done by serialization the optional<T> as optional BOOST_STATIC_ASSERT( boost::serialization::detail::is_default_constructible<T>::value || boost::is_pointer<T>::value ); The code snippet: #include #include #include #include #include <fstream> int main(int argc, char *argv[]) { (void)argc; (void)argv; typedef boost::archive::text_oarchive oarchive_type; typedef boost::archive::text_iarchive iarchive_type; std::ios_base::openmode flags = std::ios_base::openmode(); { std::ofstream ofs("/tmp/tmp.bin", std::ios::out | flags); boost::optionalstd::string s = std::string("hello"); oarchive_type oa(ofs); oa << s; } { std::ifstream ifs("/tmp/tmp.bin", std::ios::in | flags); boost::optionalstd::string s; iarchive_type ia(ifs); // # ERROR # ia >> s; } } -- Sent from: http://boost.2283326.n4.nabble.com/Boost-Users-f2553780.html

Robert Ramey

4:57 p.m.

On 2/19/18 4:35 AM, Chardrazle via Boost-users wrote:

...

As part of upgrading a product to a later version of boost the compilation has tripped up on serialization of a boost::optionalstd::string.

The /optional.hpp/ header now has the comment:

...and this fires for std::string.

What, if any, is the recommended way forward for this?

Hmmm- is std::string not default constructible?

Chardrazle

20 Feb 20 Feb

9:41 a.m.

Indeed, and my initial workaround was to force that through: It may be related to: https://svn.boost.org/trac10/ticket/13108 (is_default_constructible support.) Time to start muddying the waters. (Note: the binary archives were taken from the latest serialization 'test' code area.) Some test code: #include #include #include <fstream> #if 1 #include "boost/portable_binary_iarchive.hpp" #include "boost/portable_binary_oarchive.hpp" typedef portable_binary_oarchive oarchive_type; typedef portable_binary_iarchive iarchive_type; std::ios_base::openmode flags = std::ios::binary; #else #include #include typedef boost::archive::text_oarchive oarchive_type; typedef boost::archive::text_iarchive iarchive_type; std::ios_base::openmode flags = std::ios_base::openmode(); #endif #if (BOOST_VERSION >= 106400) && (__GNUC__*100 + __GNUC_MINOR__ == 406) namespace boost { namespace serialization { namespace detail { template <> struct is_default_constructiblestd::string : boost::true_type {}; }}} #endif int main(int argc, char *argv[]) { (void)argc; (void)argv; { std::ofstream ofs("/tmp/tmp.bin", std::ios::out | flags); boost::optionalstd::string s = std::string("hello"); oarchive_type oa(ofs); oa << s; } { std::ifstream ifs("/tmp/tmp.bin", std::ios::in | flags); boost::optionalstd::string s; iarchive_type ia(ifs); // # CRASH for binary # ia >> s; } } To work around the static_assertion, I tried adding the (serialization) specialization for is_default_constructiblestd::string. This then gets everything to compile, and the text_archive version doesn't have any problems. However, the binary_archive version crashes when trying to de-serialize. ( basic_binary_iprimitive.ipp(107): s.resize(l); ) I was concerned that the specialization has activated something undesirable, hence my question about the correct way forward... -- Sent from: http://boost.2283326.n4.nabble.com/Boost-Users-f2553780.html

Robert Ramey

4:56 p.m.

On 2/20/18 1:41 AM, Chardrazle via Boost-users wrote:

...

Indeed, and my initial workaround was to force that through:

It may be related to: https://svn.boost.org/trac10/ticket/13108 (is_default_constructible support.)

Time to start muddying the waters. (Note: the binary archives were taken from the latest serialization 'test' code area.)

Your on the right track here. Note that the boost regression tests http://www.boost.org/development/tests/develop/developer/serialization.html show serialization of optional passing with all archives - including the binary one. So it seems that this is an issue related to portable_binary_archive which has the status and example not being currently being tested on a regular basis. In theory, the code in archive implementations should be totally agnostic to the data type being serialized. Alas, s*** happens. I would recommend tracing with the debugger trough serialization of optional<string> in portable binary archive to see how it's different from serialization in binary or text archive. I've been wanting to promote portable_binary_archive to "offically supported" status, but I can't justify spending the time. Robert Ramey

Chardrazle

21 Feb 21 Feb

8:54 a.m.

...

I've been wanting to promote portable_binary_archive to "offically supported" status, but I can't justify spending the time.

This is why I thought I'd better post here, rather than going straight to trac :) I'm glad I did. I performed some further investigation by trying the sample code on my home set-up, with variations of g++ versions. I found no problems whatsoever with the portable_binary_archive. I suspect that whatever configuration has been used at the company has really messed up something to do with memory management. -- Sent from: http://boost.2283326.n4.nabble.com/Boost-Users-f2553780.html

Chardrazle

1:06 p.m.

...

I would recommend tracing with the debugger trough serialization of optional<string> in portable binary archive to see how it's different from serialization in binary or text archive.

I've performed a bit more analysis and it looks like serialization of optional<> with any non-trivial types is broken in 1.64. The serialization/optional.hpp load function: template void load( Archive & ar, boost::optional< T > & t, const unsigned int /*version*/ )[...] In 1.63, constructed space for the type with: detail::stack_construct aux(ar, item_version); ar >> boost::serialization::make_nvp("value", aux.reference()); t.reset(aux.reference()); which ensures the constructor is called. However, for 1.64 this changed to: detail::stack_allocate<T> tp; // <<<<<<<<<<<<<< ar >> boost::serialization::make_nvp("value", tp.reference()); t.reset(boost::move(tp.reference())); ar.reset_object_address( t.get_ptr(), & tp.reference() ); Unfortunately, this only allocates (zero'd) space for the object, and some objects (in this case, std::string in g++ 4.6) are not valid as such. I see that in 1.65 this changed again, to the simpler: if(! t.is_initialized()) t = T(); ar >> boost::serialization::make_nvp("value", *t); It seems I was just unlucky to choose 1.64. I've moved to 1.66 and it's all working. -- Sent from: http://boost.2283326.n4.nabble.com/Boost-Users-f2553780.html

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Chardrazle
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