STL Copy

[Derek Baker]

Can anyone see anything wrong with this from a standard C++ point of view:

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

void addToMap(map<in t,string>& m,int index, const char* str)
{
string strcast(str);
pair<int,string > p (index,str);
m.insert(p);
}

ostream& operator << (ostream& os, const pair<int,string >& p)
{
os << p.first << ": " << p.second << endl;
return os;
}

int main(void)
{
map<int, string> strings;
addToMap(string s,3,"Hello");
addToMap(string s,5,"World");

ostream_iterato r< pair<int,string > > out_it(cout,"") ;
copy(strings.be gin(),strings.e nd(),out_it); /* won't compile */

return 0;
}

This is not actually my code, but that of a poster to a forum. After
screwing up a response to that post, I'd like to help find an answer. :)

If you want to see the thread:

http://sourceforge.net/forum/forum.php?thread_id=973964&forum_id=48211

Thanks in advance.
--
Derek

[Victor Bazarov]

Re: STL Copy

"Derek Baker" <me@XYZderekbak er.eclipse.co.u k> wrote...[color=blue]
> Can anyone see anything wrong with this from a standard C++ point of view:
>
> #include <iostream>
> #include <string>
> #include <map>
> #include <iterator>
> using namespace std;
>
> void addToMap(map<in t,string>& m,int index, const char* str)
> {
> string strcast(str);
> pair<int,string > p (index,str);
> m.insert(p);
> }
>
> ostream& operator << (ostream& os, const pair<int,string >& p)
> {
> os << p.first << ": " << p.second << endl;
> return os;
> }
>
> int main(void)
> {
> map<int, string> strings;
> addToMap(string s,3,"Hello");
> addToMap(string s,5,"World");
>
> ostream_iterato r< pair<int,string > > out_it(cout,"") ;
> copy(strings.be gin(),strings.e nd(),out_it); /* won't compile */
>
> return 0;
> }
>
> This is not actually my code, but that of a poster to a forum. After
> screwing up a response to that post, I'd like to help find an answer. :)
>
> If you want to see the thread:
>
> http://sourceforge.net/forum/forum.p...forum_id=48211[/color]

The problem is that the compiler is not considering the global
namespace when it's looking for a suitable operator<<. It's a hole
in the look-up rules, or so I heard. It can be cured by an illegal
(from the standard point of view) trick: place the operator<< you
defined in the namespace std. The trick is illegal because you are
not supposed to put anything in std, only the implementation may.

Of course, it's entirely possible that I just don't remember the
legal way out of that problem.

Victor

[Derek Baker]

Re: STL Copy

"Victor Bazarov" <v.Abazarov@com Acast.net> wrote in message
news:AvBub.2433 77$Tr4.726518@a ttbi_s03...[color=blue]
> "Derek Baker" <me@XYZderekbak er.eclipse.co.u k> wrote...[color=green]
> > Can anyone see anything wrong with this from a standard C++ point of[/color][/color]
view:[color=blue][color=green]
> >
> > #include <iostream>
> > #include <string>
> > #include <map>
> > #include <iterator>
> > using namespace std;
> >
> > void addToMap(map<in t,string>& m,int index, const char* str)
> > {
> > string strcast(str);
> > pair<int,string > p (index,str);
> > m.insert(p);
> > }
> >
> > ostream& operator << (ostream& os, const pair<int,string >& p)
> > {
> > os << p.first << ": " << p.second << endl;
> > return os;
> > }
> >
> > int main(void)
> > {
> > map<int, string> strings;
> > addToMap(string s,3,"Hello");
> > addToMap(string s,5,"World");
> >
> > ostream_iterato r< pair<int,string > > out_it(cout,"") ;
> > copy(strings.be gin(),strings.e nd(),out_it); /* won't compile */
> >
> > return 0;
> > }
> >
> > This is not actually my code, but that of a poster to a forum. After
> > screwing up a response to that post, I'd like to help find an answer. :)
> >
> > If you want to see the thread:
> >
> > http://sourceforge.net/forum/forum.p...forum_id=48211[/color]
>
> The problem is that the compiler is not considering the global
> namespace when it's looking for a suitable operator<<. It's a hole
> in the look-up rules, or so I heard. It can be cured by an illegal
> (from the standard point of view) trick: place the operator<< you
> defined in the namespace std. The trick is illegal because you are
> not supposed to put anything in std, only the implementation may.
>
> Of course, it's entirely possible that I just don't remember the
> legal way out of that problem.
>
> Victor
>
>[/color]

Thanks Victor,

Someone had actually posted the answer to the forum, just after my post
here. Though without your fuller explanation.

--
Derek