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

From: Edward Diener (eldiener_at_[hidden])
Date: 2021-04-08 01:58:51

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.

> 
> On Thu, 8 Apr 2021, 04:30 Edward Diener via Boost-users, 
> <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.
>