How to resolve " undefined reference to `std::__throw_bad_cast()'"

[TridentTD]

• What is the issue you have?

I can compile well on ESP8266's xtensa_gcc compiler version5.1.0,
however when I want to receive string by dump() function .
It occurs some errors. How to resolve it?

• Please describe the steps to reproduce the issue. Can you provide a small but working code example?

First I try this code

json j = {  {"pi", 3.141}, {"happy", true}, {"name", "testtest"}, 
                    {"nothing", nullptr}, { "answer", { {"everything", 42} } },
                    {"list", {1, 0, 2}}, { "object", { {"currency", "USD"}, {"value", 42.99} } } };

Serial.println((float) j["pi"],3);     // print to Serial Monitor

The result can print well on Serial Monitor --> 3.141
However when I want to dump like the following.

std::string dump_string =  j.dump();

It occurs error like this

libstdc++.a(ostream-inst.o): In function `std::ostream& std::ostream::_M_insert<long>(long)':
libstdc++-v3/include/ostream:544: undefined reference to `std::__throw_bad_cast()'
libstdc++.a(wlocale-inst.o): In function `std::ctype<wchar_t> const& std::use_facet<std::ctype<wchar_t> >(std::locale const&)':
libstdc++-v3/include/bits/locale_facets_nonio.tcc:1173: undefined reference to `std::__throw_bad_cast()'
...

How to resolve "undefined reference to `std::__throw_bad_cast()' " error ?

Thank you.

[nlohmann]

As wchar_t are mentioned: the return type of j.dump() is std::string - I am not sure about Serial.println, but if it expects wchar_t, this may be a problem. Quick googling also found this issue: https://stackoverflow.com/questions/22263732/undefined-reference-to-stdbad-castbad-cast

Can you compile and execute the test suite?

[TridentTD]

My Serial.println() already know std::string

But when call j.dump() , it occurs std::__throw_bad_cast() error.

How can I change about THROW or anything like that to null String when it can't casting?

[nlohmann]

This seems to be an issue with the compiler.

Maybe related:

• https://stackoverflow.com/questions/48942615/errors-using-stringstream-with-esp8266-arduino-ide
• Missing __throw_bad_cast stub esp8266/Arduino#3358

[TridentTD]

Thank you.

It seems to be an issue by c++ compiler config / flags.
If I take "noexcept" flag , is there any problem for the json library ?

[nlohmann]

You mean -fno-exceptions? That works, but please note that without exceptions, the library will abort in case of an error.

[TridentTD]

I've already tried , but std::__throw_bad_cast() errors still occur.

[nlohmann]

According to esp8266/Arduino#3358 the problem could be the usage of string streams. They are used in three locations in the code - each only in case of an error. You could try to change these locations by replacing ss.str() with "" and removing all std::stringstream occurrences. If this helps, we may get rid of string streams altogether.

[nlohmann]

@TridentTD Could you check the most recent develop version? With #1117, we removed stringstreams.

[TridentTD]

By the most recent develop version,
I used the simgle include for testing.

Result :

[nlohmann]

Then I have no idea how to proceed.

[TridentTD]

Do you mind to use Arduino's String (WString.h/ WString.cpp)
instread of std::string for Arduino user ?

Thank you.

[nlohmann]

@TridentTD You can template the string type for the JSON library yourself.

[nlohmann]

@TridentTD Do you need any further assistance?

[TridentTD]

@nlohmann
I have alread ported Arduino-Core's WString library for using on any other C++ platform.
https://github.com/TridentTD/Arduino_WString/

But my knowledge about C++ template is very little, and about std::string or std::__throw_bad_cast() too,
So I don't know how to replace std:string and std::__throw_bad_cast() by Arduino' WString library.

[pboettch]

On an embedded platform where there is no standard library and no standard crt0 you need to provide your own implemention of basic "system" functions. That's why it is a link error and not a compile error.

Arduino's libraries should provide it but it seems they don't.

Just put a function like this in your application:

namespace std {

void __throw_bad_cast(void)
{
    // print error and stop execution
}

} // namespace std

Not sure about the prototype though.

[nlohmann]

@TridentTD Any news on this?

[nlohmann]

@TridentTD Does esp8266/Arduino#3358 (comment) work for you?

[nlohmann]

@TridentTD Any news on this?