On 19 Oct, 23:28, mojmir <svobod...@gmail.com> wrote:
hello,
i am trying to dump whole map container to ostream like this:
template<typename T, typename U>
inline
std::ostream & operator<< (std::ostream & s, std::pair<T,U> const & p)
{
s << "<" << p.first << "," << p.second << ">";
return s;
}
template<typename K, typename T>
inline
std::ostream & operator<< (std::ostream & s, std::map<K,T> const & m)
{
s << "(";
typedef typename std::map<K,T>::value_type t;
std::copy(m.begin(), m.end(), std::ostream_iterator<t>(s, " "));
s << ")";
return s;
}
but the copy line fails to compile and i am unable to guess why.
I assume that you have the correct #includes?
#include <algorithm> // For std::copy
#include <iterator> // For std::ostream_iterator
#include <map> // For std::map
#include <ostream> // For std::ostream
#include <utility> // For std::pair
Beyond that, whether the code works or not will depend exactly what
your test case looks like, but there definitely is scope to be bitten
by a fairly subtle problem. The following test case, for example,
should exhibit the problem:
#include <iostream>
#include <string>
int main() {
std::map< std::string, int > m;
std::cout << m;
}
The fundamental problem is to do with name lookup of operator<<, and
because you have put it in the global namespace it is not being
found. The short answer is that you can fix this by moving the two
operator<<s into namespace std -- technically this isn't legal as
you're not really allowed to put overloaded operators into namespace
std, but it's probably the least worst solution.
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