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

From: Edward Diener (eldiener_at_[hidden])
Date: 2021-04-09 12:58:28

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 :
> 
>  1.
>     #include <boost/variant.hpp>
>  2.
>     #include <string>
>  3.
>     #include <iostream>
>  4.
>     std::ostream& operator<<(std::ostream& o, const __int128& x) { if (x
>     == std::numeric_limits<__int128>::min()) return o <<
>     "-170141183460469231731687303715884105728"; if (x < 0) return o <<
>     "-" << -x; if (x < 10) return o << (char)(x + '0'); return o << x /
>     10 << (char)(x % 10 + '0'); }
>  5.
>     int main()
>  6.
>     {
>  7.
>     boost::variant<__int128, char, std::string> v;
>  8.
>     v = 56;
>  9.
>     v = 'Y';
> 10.
>     __int128 d=12;
> 11.
>     std::cout <<d << '\n';
> 12.
>     std::cout << v << '\n';
> 13.
>     v = "Yashaswi raj";
> 14.
>     std::cout << v << '\n';
> 15.
>     }
> 
> If u replace __int128 with int in the variant variable, it seems to work 
> just fine...

As others have pointed out, the correct code is:

#include <boost/variant.hpp>
#include <string>
#include <iostream>

namespace std
{

std::ostream& operator<<(std::ostream& o, const __int128& x)
     {
     if (x == std::numeric_limits<__int128>::min()) return o << 
"-170141183460469231731687303715884105728";
     if (x < 0) return o << "-" << -x;
     if (x < 10) return o << (char)(x + '0');
     return o << x / 10 << (char)(x % 10 + '0');
     }

}

int main()
{

boost::variant<__int128, char, std::string> v;
v = static_cast<__int128>(56);
v = 'Y';
__int128 d=12;
std::cout << d << '\n';
std::cout << v << '\n';
v = "Yashaswi raj";
std::cout << v << '\n';
return 0;
}

So __int128 does indeed work with variant, as I originally surmised.

> 
> On Thu, 8 Apr 2021, 00:10 Edward Diener via Boost-users, 
> <boost-users_at_[hidden] <mailto:boost-users_at_[hidden]>> wrote:
> 
>     On 4/7/2021 2:15 PM, Anil Muthigi via Boost-users wrote:
>      > I dont think so...
> 
>     If it is available why do you think variant would not support it ?
> 
>      > I guess int128_t under boost/multiprecision/cpp_int is the only
>     viable
>      > option.
>      >
>      > On Wed, 7 Apr 2021, 11:39 pm David Frank via Boost-users,
>      > <boost-users_at_[hidden] <mailto:boost-users_at_[hidden]>
>     <mailto:boost-users_at_[hidden]
>     <mailto:boost-users_at_[hidden]>>> wrote:
>      >
>      >Â  Â  Â especially the gnu __int128?