ich verwende eine Templatefunktion

template<class K, class V> ostream& operator<<(ostream& s, const map<K, V>& mp)
{
	for (typename map<K, V>::const_iterator it = mp.begin(); it != mp.end(); ++it)
		s << (*it).first << " => " << (*it).second << "   ";
	return s;
}

um Maps mittels des Operators << ausgeben zu können. Das hat bisher insoweit funktioniert, bei der Verwendung von Namespaces ist jedoch folgendes Problem aufgetaucht: Wenn ich

class In_Out_Streams
{
	friend ostream& operator<<(ostream& s, In_Out_Streams& ios);
	...
};

in einen Namespace IO setze, so erhalte ich dann beim Kompilieren von

namespace IO {
	void f()
	{
		map<string, string> dirs;
		cout << dirs << endl;   // FEHLER
	}
}

die Fehlermeldung

Building file: ../src/IO/files.cpp
Invoking: GCC C++ Compiler
g++ -I../../../boost -I../../../gsl/include -I../../../log4cxx/src/main/include -I../ -I../src -I../src/classification -I../src/IO -I../src/node -I../src/tree -O0 -g3 -c -fmessage-length=0 -ansi -MMD -MP -MF"src/IO/files.d" -MT"src/IO/files.d" -o"src/IO/files.o" "../src/IO/files.cpp"
../src/IO/files.cpp: In function ‘void IO::f()’:
../src/IO/files.cpp:350: error: no match for ‘operator<<’ in ‘std::cout << dirs’
/usr/include/c++/4.1.2/bits/ostream.tcc:67: note: candidates are: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(std::basic_ostream<_CharT, _Traits>& (*)(std::basic_ostream<_CharT, _Traits>&)) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/include/c++/4.1.2/bits/ostream.tcc:78: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(std::basic_ios<_CharT, _Traits>& (*)(std::basic_ios<_CharT, _Traits>&)) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/include/c++/4.1.2/bits/ostream.tcc:90: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(std::ios_base& (*)(std::ios_base&)) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/include/c++/4.1.2/bits/ostream.tcc:241: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(long int) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/include/c++/4.1.2/bits/ostream.tcc:264: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(long unsigned int) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/include/c++/4.1.2/bits/ostream.tcc:102: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(bool) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/include/c++/4.1.2/bits/ostream.tcc:125: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(short int) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/include/c++/4.1.2/bits/ostream.tcc:157: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(short unsigned int) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/include/c++/4.1.2/bits/ostream.tcc:183: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(int) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/include/c++/4.1.2/bits/ostream.tcc:215: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(unsigned int) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/include/c++/4.1.2/bits/ostream.tcc:288: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(long long int) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/include/c++/4.1.2/bits/ostream.tcc:311: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(long long unsigned int) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/include/c++/4.1.2/bits/ostream.tcc:361: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(double) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/include/c++/4.1.2/bits/ostream.tcc:335: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(float) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/include/c++/4.1.2/bits/ostream.tcc:384: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(long double) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/include/c++/4.1.2/bits/ostream.tcc:407: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(const void*) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/include/c++/4.1.2/bits/ostream.tcc:430: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(std::basic_streambuf<_CharT, _Traits>*) [with _CharT = char, _Traits = std::char_traits<char>]
../src/IO/files.cpp:316: note:                 std::ostream& IO::operator<<(std::ostream&, IO::In_Out_Streams&)
make: *** [src/IO/files.o] Error 1

Wenn ich f in einen anderen Namespace setze oder keinen Left-Shift-Operator für In_Out_Streams definiere, taucht das Problem nicht auf.

Weiss jemand, was hier los ist und wie man es behebt?