ciao, ho fatto cme dici ma dà come errori:

error: no matching function for call to ‘std::basic_ofstream<char, std::char_traits<char> >::basic_ofstream(std::string&, const std::_Ios_Openmode&)’
/usr/include/c++/4.3/fstream:572: note: candidates are: std::basic_ofstream<_CharT, _Traits>::basic_ofstream(const char*, std::_Ios_Openmode) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/include/c++/4.3/fstream:556: note: std::basic_ofstream<_CharT, _Traits>::basic_ofstream() [with _CharT = char, _Traits = std::char_traits<char>]
/usr/include/c++/4.3/iosfwd:89: note: std::basic_ofstream<char, std::char_traits<char> >::basic_ofstream(const std::basic_ofstream<char, std::char_traits<char> >&)
applications/udpapp/UDPClusterApp.cc: In member function ‘virtual void UDPClusterApp::finish()’:
applications/udpapp/UDPClusterApp.cc:465: warning: comparison between signed and unsigned integer expressions

dove la riga d errore è:

ofstream NomeClasse::transition_file(file,ios::app);

(li sto usando in modo static)