Re: does boost::variant support 128 bit integer?

From: Edward Diener (eldiener_at_[hidden])
Date: 2021-04-08 14:37:10

On 4/7/2021 10:33 PM, Anil Muthigi via Boost-users wrote:
> But I am not even doing any kind of input or output using __int128 FOR 
> THE VARIANT VARIABLE….
> 
> As you can see… if you choose to use int instead of __int128 for the 
> VARIANT VARIABLE and rerun the code…. it is actually printing the value 
> of the __int128 variable d which I have used in the code..
>  Â So, I guess it is actually picking up my std::ostream& 
> operator<<(std::ostream& o, const __int128& x) functionality.

I agree that variant does not support __int128. File a Issue report at 
https://github.com/boostorg/variant if you wish. I am not the variant 
maintainer. You may also try variant2.

> 
>> On 08-Apr-2021, at 7:52 AM, Edward Diener via Boost-users 
>> <boost-users_at_[hidden] <mailto:boost-users_at_[hidden]>> wrote:
>>
>> On 4/7/2021 9:58 PM, Edward Diener via Boost-users wrote:
>>> On 4/7/2021 7:10 PM, Anil Muthigi via Boost-users wrote:
>>>> If u see my code,  I have used __int128 separately for the variable 
>>>> d as well. If u change the variant variable' s data type from 
>>>> __int128 to int , it will run just fine.
>>> The reason your code is failing is because your stream operator uses 
>>> streaming and __int128 has no stream support. If you use an __int128 
>>> in a variant, but never use streaming, your code is fine. I do not 
>>> know the reason why gcc and clang support __int128 but do not support 
>>> the the type in streaming. Maybe you should try asking gcc about it 
>>> or investigate it as a stackoverflow question.
>>> Please do not topmost.
>>
>> Apologies ! It looks as if the variant i/o is simply not picking up 
>> your std::ostream& operator<<(std::ostream& o, const __int128& x) 
>> functionality. I tried putting your functionality in namespace boost 
>> but it still did not pick it up.
>>
>>>>
>>>> On Thu, 8 Apr 2021, 04:30 Edward Diener via Boost-users, 
>>>> <boost-users_at_[hidden] <mailto:boost-users_at_[hidden]> 
>>>> <mailto:boost-users_at_[hidden] 
>>>> <mailto:boost-users_at_[hidden]>>> wrote:
>>>>
>>>> On 4/7/2021 3:38 PM, Anil Muthigi via Boost-users wrote:
>>>> > I said that I am not sure if boost::variant supports __int128
>>>> because I
>>>> > had difficulties in compiling this code :
>>>> >
>>>> >Â  1.
>>>> >Â  Â  Â #include <boost/variant.hpp>
>>>> >Â  2.
>>>> >Â  Â  Â #include <string>
>>>> >Â  3.
>>>> >Â  Â  Â #include <iostream>
>>>> >Â  4.
>>>> >Â  Â  Â std::ostream& operator<<(std::ostream& o, const __int128& x)
>>>> { if (x
>>>> >Â  Â  Â == std::numeric_limits<__int128>::min()) return o <<
>>>> >Â  Â  Â "-170141183460469231731687303715884105728"; if (x < 0) return
>>>> o <<
>>>> >Â  Â  Â "-" << -x; if (x < 10) return o << (char)(x + '0'); return o
>>>> << x /
>>>> >Â  Â  Â 10 << (char)(x % 10 + '0'); }
>>>> >Â  5.
>>>> >Â  Â  Â int main()
>>>> >Â  6.
>>>> >Â  Â  Â {
>>>> >Â  7.
>>>> >Â  Â  Â boost::variant<__int128, char, std::string> v;
>>>> >Â  8.
>>>> >Â  Â  Â v = 56;
>>>> >Â  9.
>>>> >Â  Â  Â v = 'Y';
>>>> > 10.
>>>> >Â  Â  Â __int128 d=12;
>>>> > 11.
>>>> >Â  Â  Â std::cout <<d << '\n';
>>>> > 12.
>>>> >Â  Â  Â std::cout << v << '\n';
>>>> > 13.
>>>> >Â  Â  Â v = "Yashaswi raj";
>>>> > 14.
>>>> >Â  Â  Â std::cout << v << '\n';
>>>> > 15.
>>>> >Â  Â  Â }
>>>> >
>>>> > If u replace __int128 with int in the variant variable, it seems
>>>> to work
>>>> > just fine...
>>>>
>>>> My test with gcc-10.2 and clang-linux-11.0 shows that it does not
>>>> support __int128 in iostreams.
>>>>
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