warnings in MSVC (2015) in 3.4.0 related to bool...

[ziggurat29]

I just updated to 3.4.0 from 3.3.0 and some new warnings have appeared that were not present before.
They relate to 'bool'; MSVC warns if there is a integral type demoted to 'bool' type.
These were emitted in 3.3.0.

c:\experiments\sixengines\gits\forethoughtengine001\forethoughtengine001\forethoughtenginelib001\product\../srclibs/json/json.hpp(6585): warning C4800: 'int': forcing value to bool 'true' or 'false' (performance warning)
  c:\experiments\sixengines\gits\forethoughtengine001\forethoughtengine001\forethoughtenginelib001\product\../srclibs/json/json.hpp(6557): note: while compiling class template member function 'bool nlohmann::detail::binary_reader<nlohmann::basic_json<std::map,std::vector,std::string,bool,int64_t,uint64_t,double,std::allocator,nlohmann::adl_serializer>,SAX>::parse_bson_element_internal(const int,const std::size_t)'
          with
          [
              SAX=`anonymous-namespace'::sax_lua_tbl_builder
          ]
  c:\experiments\sixengines\gits\forethoughtengine001\forethoughtengine001\forethoughtenginelib001\product\../srclibs/json/json.hpp(6650): note: see reference to function template instantiation 'bool nlohmann::detail::binary_reader<nlohmann::basic_json<std::map,std::vector,std::string,bool,int64_t,uint64_t,double,std::allocator,nlohmann::adl_serializer>,SAX>::parse_bson_element_internal(const int,const std::size_t)' being compiled
          with
          [
              SAX=`anonymous-namespace'::sax_lua_tbl_builder
          ]
  c:\experiments\sixengines\gits\forethoughtengine001\forethoughtengine001\forethoughtenginelib001\product\../srclibs/json/json.hpp(18390): note: see reference to class template instantiation 'nlohmann::detail::binary_reader<nlohmann::basic_json<std::map,std::vector,std::string,bool,int64_t,uint64_t,double,std::allocator,nlohmann::adl_serializer>,SAX>' being compiled
          with
          [
              SAX=`anonymous-namespace'::sax_lua_tbl_builder
          ]
  product\lua_runtime_setup.cpp(464): note: see reference to function template instantiation 'bool nlohmann::basic_json<std::map,std::vector,std::string,bool,int64_t,uint64_t,double,std::allocator,nlohmann::adl_serializer>::sax_parse<`anonymous-namespace'::sax_lua_tbl_builder>(nlohmann::detail::input_adapter &&,SAX *,nlohmann::basic_json<std::map,std::vector,std::string,bool,int64_t,uint64_t,double,std::allocator,nlohmann::adl_serializer>::input_format_t,const bool)' being compiled
          with
          [
              SAX=`anonymous-namespace'::sax_lua_tbl_builder
          ]
  product\lua_runtime_setup.cpp(464): note: see reference to function template instantiation 'bool nlohmann::basic_json<std::map,std::vector,std::string,bool,int64_t,uint64_t,double,std::allocator,nlohmann::adl_serializer>::sax_parse<`anonymous-namespace'::sax_lua_tbl_builder>(nlohmann::detail::input_adapter &&,SAX *,nlohmann::basic_json<std::map,std::vector,std::string,bool,int64_t,uint64_t,double,std::allocator,nlohmann::adl_serializer>::input_format_t,const bool)' being compiled
          with
          [
              SAX=`anonymous-namespace'::sax_lua_tbl_builder
          ]

As you can probably gather, I have a sax parser:

class sax_lua_tbl_builder : public nlohmann::json::json_sax_t

which I use to convert a JSON document into another form.

For the time being, I have wrapped the header like this:

#pragma warning ( push )
#pragma warning ( disable: 4800 )
#include "../srclibs/json/json.hpp"
#pragma warning ( pop )

since it seems like I can safely ignore it, but I figured you might like to know about the issue to do some sort of proper fix. Especially because this warning was NOT emitted in the previous version (3.3.0).

[nlohmann]

Thanks for reporting! The warnings stems from the BSON parser which was indeed introduced in version 3.4.0.

The line (json.hpp:6585) in question is

return sax->boolean(static_cast<bool>(get()));

and by changing it to

return sax->boolean(get() != 0);

the warning should go away. Strange that it is not displayed in the AppVeyor log.

@ziggurat29 Could you please try whether the proposed change fixes the warning?

[ziggurat29]

your change is confirmed; thanks for fixing! -dave

…

-----Original Message----- From: Niels Lohmann [mailto:notifications@github.com] Sent: Tuesday, November 20, 2018 11:46 AM To: nlohmann/json Cc: ziggurat29; Mention Subject: Re: [nlohmann/json] warnings in MSVC (2015) in 3.4.0 related to bool... (#1364) Thanks for reporting! The warnings stems from the BSON parser which was indeed introduced in version 3.4.0. The line (json.hpp:6585) in question is return sax->boolean(static_cast<bool>(get())); and by changing it to return sax->boolean(get() != 0); the warning should go away. Strange that it is not displayed in the AppVeyor log <https://ci.appveyor.com/project/nlohmann/json/build/job/s0v47i69ldofcwpb?fu llLog=true> . @ziggurat29 <https://github.com/ziggurat29> Could you please try whether the proposed change fixes the warning? - You are receiving this because you were mentioned. Reply to this email directly, view <#1364 (comment)> it on GitHub, or mute <https://github.com/notifications/unsubscribe-auth/Ac6BFbKsZvhp-DxSKJsUdUu5j RFT58q1ks5uxD6TgaJpZM4Yp0tL> the thread. <https://github.com/notifications/beacon/Ac6BFR4qSzaSpdZ5P1YOEz2I5Ww0RaY3ks5 uxD6TgaJpZM4Yp0tL.gif>

[nlohmann]

Thanks for checking back!