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

From: Edward Diener (eldiener_at_[hidden])
Date: 2021-04-08 02:22:07

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]>> wrote:
>>
>> Â Â Â  On 4/7/2021 3:38 PM, Anil Muthigi via Boost-users wrote:
>> Â Â Â Â  > I said that I am not sure if boost::variant supports __int128
>> Â Â Â  because I
>> Â Â Â Â  > had difficulties in compiling this code :
>> Â Â Â Â  >
>> Â Â Â Â  >Â  1.
>> Â Â Â Â  >Â  Â  Â #include <boost/variant.hpp>
>> Â Â Â Â  >Â  2.
>> Â Â Â Â  >Â  Â  Â #include <string>
>> Â Â Â Â  >Â  3.
>> Â Â Â Â  >Â  Â  Â #include <iostream>
>> Â Â Â Â  >Â  4.
>> Â Â Â Â  >Â  Â  Â std::ostream& operator<<(std::ostream& o, const __int128& x)
>> Â Â Â  { if (x
>> Â Â Â Â  >Â  Â  Â == std::numeric_limits<__int128>::min()) return o <<
>> Â Â Â Â  >Â  Â  Â "-170141183460469231731687303715884105728"; if (x < 0) return
>> Â Â Â  o <<
>> Â Â Â Â  >Â  Â  Â "-" << -x; if (x < 10) return o << (char)(x + '0'); return o
>> Â Â Â  << x /
>> Â Â Â Â  >Â  Â  Â 10 << (char)(x % 10 + '0'); }
>> Â Â Â Â  >Â  5.
>> Â Â Â Â  >Â  Â  Â int main()
>> Â Â Â Â  >Â  6.
>> Â Â Â Â  >Â  Â  Â {
>> Â Â Â Â  >Â  7.
>> Â Â Â Â  >Â  Â  Â boost::variant<__int128, char, std::string> v;
>> Â Â Â Â  >Â  8.
>> Â Â Â Â  >Â  Â  Â v = 56;
>> Â Â Â Â  >Â  9.
>> Â Â Â Â  >Â  Â  Â v = 'Y';
>> Â Â Â Â  > 10.
>> Â Â Â Â  >Â  Â  Â __int128 d=12;
>> Â Â Â Â  > 11.
>> Â Â Â Â  >Â  Â  Â std::cout <<d << '\n';
>> Â Â Â Â  > 12.
>> Â Â Â Â  >Â  Â  Â std::cout << v << '\n';
>> Â Â Â Â  > 13.
>> Â Â Â Â  >Â  Â  Â v = "Yashaswi raj";
>> Â Â Â Â  > 14.
>> Â Â Â Â  >Â  Â  Â std::cout << v << '\n';
>> Â Â Â Â  > 15.
>> Â Â Â Â  >Â  Â  Â }
>> Â Â Â Â  >
>> Â Â Â Â  > If u replace __int128 with int in the variant variable, it seems
>> Â Â Â  to work
>> Â Â Â Â  > just fine...
>>
>> Â Â Â  My test with gcc-10.2 and clang-linux-11.0 shows that it does not
>> Â Â Â  support __int128 in iostreams.
>>
> 
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