using dump() when std::wstring is StringType with VS2017

[TobiSchluter]

I may be doing something stupid, but I'm trying to use std::wstring as my string type. If I call json::dump on my wstring'ed json object, it seems to not be able to convert from char to wchar_t if I correctly understand an error message that is too verbose to not be opaque. I quote the errors at the bottom. This is with VisualStudio 2017. I cloned the git repo a few weeks ago, and haven't tried with the latest version, but I didn't see any pertinent checkins in the meantime. I may have missed them of course. Likewise for examples that use a different string type, I also didn't find any closed issues referring to wchar_t or std::wstring.

My declarations look like:

        namespace utility { typedef string_t std::wstring; }
        nlohmann::basic_json<std::map, std::vector, utility::string_t> j = njson::parse(wbody); // here wbody is of type std::wstring

and the call to dump is
utility::string_t dump = j.dump(0); // again utility::string_t is std::wstring.

Is this expected?

Thank you for your good work. The library has really made my life a lot easier.

(The first warning always appears when including the header, and is unrelated.)

1>C:\tobi\Source\json/json.hpp(5961): warning C4819: The file contains a character that cannot be represented in the current code page (932). Save the file in Unicode format to prevent data loss
1>C:\tobi\Source\json/json.hpp(8999): error C2440: '<function-style-cast>': cannot convert from 'std::basic_string<wchar_t,std::char_traits<wchar_t>,std::allocator<wchar_t>>' to 'nlohmann::detail::output_adapter<char>'
1>C:\tobi\Source\json/json.hpp(8999): note: No constructor could take the source type, or constructor overload resolution was ambiguous
1>C:\tobi\Source\json/json.hpp(8997): note: while compiling class template member function 'std::basic_string<wchar_t,std::char_traits<wchar_t>,std::allocator<wchar_t>> nlohmann::basic_json<std::map,std::vector,utility::string_t,bool,int64_t,uint64_t,double,std::allocator,nlohmann::adl_serializer>::dump(const int,const char,const bool) const'
1>C:\tobi\Source\source.cpp(57): note: see reference to function template instantiation 'std::basic_string<wchar_t,std::char_traits<wchar_t>,std::allocator<wchar_t>> nlohmann::basic_json<std::map,std::vector,utility::string_t,bool,int64_t,uint64_t,double,std::allocator,nlohmann::adl_serializer>::dump(const int,const char,const bool) const' being compiled
1>C:\tobi\Source\source.cpp(34): note: see reference to class template instantiation 'nlohmann::basic_json<std::map,std::vector,utility::string_t,bool,int64_t,uint64_t,double,std::allocator,nlohmann::adl_serializer>' being compiled
1>C:\tobi\Source\json/json.hpp(8999): error C2664: 'nlohmann::detail::serializer<nlohmann::basic_json<std::map,std::vector,utility::string_t,bool,int64_t,uint64_t,double,std::allocator,nlohmann::adl_serializer>>::serializer(const nlohmann::detail::serializer<nlohmann::basic_json<std::map,std::vector,utility::string_t,bool,int64_t,uint64_t,double,std::allocator,nlohmann::adl_serializer>> &)': cannot convert argument 1 from 'const char' to 'const nlohmann::detail::serializer<nlohmann::basic_json<std::map,std::vector,utility::string_t,bool,int64_t,uint64_t,double,std::allocator,nlohmann::adl_serializer>> &'
1>C:\tobi\Source\json/json.hpp(8999): note: Reason: cannot convert from 'const char' to 'const nlohmann::detail::serializer<nlohmann::basic_json<std::map,std::vector,utility::string_t,bool,int64_t,uint64_t,double,std::allocator,nlohmann::adl_serializer>>'
1>C:\tobi\Source\json/json.hpp(8999): note: No constructor could take the source type, or constructor overload resolution was ambiguous

[nlohmann]

Currently, std::wstring is not supported by the library. Even though the string type is templated, there are too many assumptions in the code that rely on using std::string. Sorry about that :-/

[TobiSchluter]

I figured that the lack of documentation on how to use arbitrary string types was no accident, so I didn't bet all my chips on this. I would have been mightily impressed if it worked though!

I don't know your policy, so I'm not going to close this issue myself, but please feel free to do so, no feelings hurt :)

[nlohmann]

In #774 there is a discussion how to improve the library toward better support of types. I hope we can find a way to cope with wstrings there.

[nlohmann]

I added an FAQ entry: https://json.nlohmann.me/home/faq/#wide-string-handling