Re: overloading << for map and multimap simultaneously

From:
"Victor Bazarov" <v.Abazarov@comAcast.net>
Newsgroups:
comp.lang.c++
Date:
Sun, 29 Jul 2007 10:06:09 -0400
Message-ID:
<EvOdnc-1ssBNAzHbnZ2dnUVZ_oKhnZ2d@comcast.com>
ozizus wrote:

I overloaded operator << for STL map successfully:

template <typename T1, typename T2> ostream & operator << (ostream &
o, map <T1,T2> & m)
{
//code
}

the code works like a charm. Now, I want the same functionality for
multimap. Since their interface is same for the problem at hand, I
want to make collection name a template parameter like this:

template <typename MAP, typename T1, typename T2> ostream & operator
<< (ostream & o, MAP<T1,T2> & m)
{
//code
}

The compiler errors like this: syntax error : missing ')' before '<'


The compiler cannot deduce all three from the argument you give.
Besides, if 'MAP' is a template (as you imply by using the template
syntax when declaring the second argument), then it's not a "typename"
argument, it's a "template <class,class> class MAP" argument. Try

template<template<class, class> class MAP, typename T1, typename T2>
ostream& operator << (...

but it is most likely not going to work. I recommend dropping the T1
and T2 arguments and just do

  template<class MAP> ostream& operator <<( ostream& o, MAP const& m)

(you do want to have the output object 'const', by the way).

V
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