[Dev-C++] ostringstream and insertion operator problem

[A D <a_...@ho...>]

Hi! I'm trying to learn c++ and stumbled upon part of a code which I'm havi=
ng
difficulties to understand:


class BadConversion : public std::runtime_error {
 public:
   BadConversion(const std::string& s)
     : std::runtime_error(s)
     { }
 };
=20
 inline std::string stringify(double x)
 {
   std::ostringstream o;
   if (!(o << x))
     throw BadConversion("stringify(double)");
   return o.str();
 }


the function stringify() converts a double number to string And returns the=
 string.=20
I'm having problem with the following line:


if (!(o << x)) //<-----------------------------------problem=20
     throw BadConversion("stringify(double)");

according to the api ostringstream is a typedef of basic_ostringstream clas=
s. This insertion (<
     basic_ostream&=20
    basic_ostream::operator<put(*this, *this, this->fill(), __n).failed())
           this->setstate(ios_base::badbit);
         }
       catch(...)
         {
           // 27.6.1.2.1 Common requirements.
           // Turn this on without causing an ios::failure to be thrown.
           this->_M_setstate(ios_base::badbit);
           if ((this->exceptions() & ios_base::badbit) !=3D 0)
         __throw_exception_again;
         }
     }
       return *this;
     }


You can  clearly see from the definition that binary operator "<<" outputs =
an=20
object of basic_ostream reference type. My question is can the operator <<=
=20
return a zero in this case? Because by definition this operator clearly ret=
urns a=20
reference object of type basic_ostream&.  If it returns zero(which is teste=
d in=20
order for a exception to be thrown in the former code shown above), shouldn=
't=20
it contradict the fact that this operator can only return an object not a n=
umber?=20
Thanks.


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