Re: Template Template Parameters and overload problems

From:
gilles Rochefort <grochefort@realeyes3d.com>
Newsgroups:
comp.lang.c++.moderated
Date:
31 Jul 2006 11:55:29 -0400
Message-ID:
<pan.2006.07.31.15.06.25.12249@realeyes3d.com>
Hi Andy,

You just have some typical const-less problem
Just change the line :
std::ostream& operator<< (std::ostream & out, std::set<int> & si)
with :
std::ostream& operator<< (std::ostream & out, const std::set<int> & si)

and it will be ok !

Explanation :
In you printone section, you consider t.second as a const argument which
is not the case from your declaration of std::operator<< . So, it is more
convenient to declare it as const; Doing such a way, your
overloading of operator<< will accept both const and non-const as a second
argument..

Regards,
Gilles

Dear readers:

I met a problem and can't solve for a long time so any advices and
suggestions will be appreciated.

#include <iostream>
#include <string>
#include <set>
#include <map>
using namespace std;

template <typename T>
void printall(T const& t)
{
    typename T::const_iterator iter;
    iter= t.begin();
    while(iter != t.end()) {
        printone(*iter);
        ++iter;
    }
    std::cout << typeid(t).name() << std::endl;
    return;
}
template <typename T, typename T1, template<typename T, typename T1>
class CONT >
void printone(const CONT<const T, T1> &t)
{
    std::cout << t.first /*<< " " << t.second */<< std::endl;
    return;
}
std::ostream& operator<< (std::ostream & out, std::set<int> & si)
{
    std::set<int>::iterator iter=si.begin();
    while(iter != si.end()) {
        out << *iter << " ";
        ++iter;
    }
    return out;
}

int main(void) {
    int di[] = {1, 3, 5, 7};
    set<int> ti(di, di+4);
    cout << ti << endl;

    map<string, set<int> > maps;
    maps["hello"] = ti;
    printall(maps);

    map<string, set<int> >::iterator iter = maps.begin();
    cout << (*iter).first << " " << (*iter).second << endl;
    return 0;
}

if I open the comment on line 22
    std::cout << t.first /*<< " " << t.second */<< std::endl;
to
    std::cout << t.first << " " << t.second << std::endl;

gcc will cry out
10.6.test.cpp:22: error: no match for 'operator<<' in 'std::operator<<
[with _Traits = std::char_traits<char>](((std::basic_ostream<char,
std::char_traits<char> >&)(+std::operator<< [with _CharT = char,
_Traits = std::char_traits<char>, _Alloc =
std::allocator<char>](((std::basic_ostream<char, std::char_traits<char>

&)(&std::cout)), ((const std::basic_string<char, std::char_traits<char>,

std::allocator<char> >&)((const std::string*)t))))), ((const char*)" "))

<<

t->std::pair<const std::string, std::set<int, std::less<int>,
std::allocator<int> > >::second'


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