Re: [Boost-users] Boost Variant OutputStreamable

From: Ovanes Markarian (om_boost_at_[hidden])
Date: 2006-06-26 07:16:00

The operator << must be defined in the boost namespace.

See the error message of VC:see reference to function template instantiation
'std::basic_ostream<_Elem,_Traits> &boost::operator
<<<char,std::char_traits<char>,std::vector<_Ty>,int,std::string,boost::detail::variant::void_,boost::detail::variant::void_,boost::detail::variant::void_,boost::detail::variant::void_,boost::detail::variant::void_,boost::detail::variant::void_,boost::detail::variant::void_,boost::detail::variant::void_,boost::detail::variant::void_,boost::detail::variant::void_,boost::detail::variant::void_,boost::detail::variant::void_,boost::detail::variant::void_,boost::detail::variant::void_,boost::detail::variant::void_,boost::detail::variant::void_,boost::detail::variant::void_>(std::basic_ostream<_Elem,_Traits>
&,const boost::variant<T0_,T1,T2> &)' being compiled

VC looks for boost::operator<< function and not ::operator<< function. But this
should be
documented in OutputStreamable.

This would compile:

#include<iostream>
#include<vector>
#include<string>

#include<boost/variant.hpp>

namespace boost
{
        template <typename T>
        std::ostream& operator<<(std::ostream& os, const std::vector<T>& v)
        {
                for(typename std::vector<T>::size_type i = 0; i < v.size(); ++i)
                        os << v[i] << std::endl;

                return os;
        }
}

struct TpTemplateVariant
{
        typedef boost::variant<std::vector<unsigned long>,int, std::string>        BoostVariant;
};

typedef TpTemplateVariant::BoostVariant Tpvariant;

int main ()
{

        Tpvariant p(5);

        std::cout << p;

        return 0;
}

Good Luck,
Ovanes Markarian

On Mon, June 26, 2006 12:45, CLAIRE, Narinder, Group Risk Mgmt wrote:
> I apologise for emailing you directly .. but i canno access the mailing list
> from work..
> However in response to your response.
>
>
> The following doesn't compile either .. I get the error
>
> error C2679: binary '<<' : no operator found which takes a right-hand
> operand of type 'const T0' (or there is no acceptable conversion)
>
> On VC8
>
> #include<iostream>
> #include<vector>
> #include<string>
>
> #include<boost/variant.hpp>
>
>
>
> std::basic_ostream<char>  &operator<<(std::basic_ostream<char>
> &theostream,const std::vector<unsigned long> &theVector) {
>         for(unsigned long i(0);i<theVector.size();i++)
>                 theostream << theVector[i] << "\n" ;
>                 return theostream;
> }
>
>
> struct TpTemplateVariant {
>                         typedef boost::variant<                std::vector<unsigned
> long>,
>
> int,
>
> std::string
>
>> BoostVariant;
> };
>
> typedef TpTemplateVariant::BoostVariant Tpvariant;
>
> int main () {
>
>         Tpvariant p(5);
>         std::cout << p;
>
>         return 0;
>
>
>
>
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