Re: Problem with defining operator<< for std::ostream_iterator

=?iso-8859-1?q?Erik_Wikstr=F6m?= <>
30 May 2007 01:04:38 -0700
On 30 Maj, 09:03, wrote:

I cannot compile the code which defines a std::map type consisting of
built in types and operator<< overload for std::map::value_type.
See the code below - I attach a full example.

Note: if I define map type with my new type (structure) everything is
OK. All compileres I've cheked report an error so I think it is a
problem with my code.

#include <algorithm>
#include <cstddef>
#include <fstream>
#include <iterator>
#include <map>

class A
        struct S // behavior similar to built-in int
                int i;
                S( int _i ) : i( _i ) {}

        typedef std::map< int, int > Map1;
        typedef std::map< int, S > Map2;

// the function below cannot be found by
// std::ostream_iterator< Map1::value_type >
friend std::ostream &operator<<(
  std::ostream &_ostr,
  const Map1::value_type &_value
    return _ostr << _value.first << ' ' << _value.second;

The type of Map1::value_type is int which means that you are trying to
overload the operator
  std::ostream &operator<<(std::ostream&, int)
To overload an operator at least one of the operands needs to be of
user-defined type (which is why it works with the second one).

Erik Wikstr=F6m

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