Hello Cory-san, Thank you for your prompt advice for my basic question. I found same thing happens even when I use dynamic bitsets as member of struct. My original simple code: #include <iostream> #include <boost/timer.hpp> #include <boost/dynamic_bitset.hpp> using namespace std; using namespace boost; struct multi_bitsets{ dynamic_bitset<> db1(10,1ul); dynamic_bitset<> db2(10,2ul); }; int main() { multi_bitsets mb1; cout<<"mb1.db1:"<<mb1.db1<<endl; cout<<"mb1.db2:"<<mb1.db2<<endl; return 0; } Long error.log: $ g++ multi_bitset_struct.org.cpp multi_bitset_struct.org.cpp:9: error: expected identifier before numeric constant multi_bitset_struct.org.cpp:9: error: expected `,' or `...' before numeric constant multi_bitset_struct.org.cpp:9: error: ISO C++ forbids declaration of `parameter' with no type multi_bitset_struct.org.cpp:10: error: expected identifier before numeric constant multi_bitset_struct.org.cpp:10: error: expected `,' or `...' before numeric constant multi_bitset_struct.org.cpp:10: error: ISO C++ forbids declaration of `parameter' with no type multi_bitset_struct.org.cpp: In function `int main()': multi_bitset_struct.org.cpp:19: error: no match for 'operator<<' in 'std::operator<< [with _Traits = std::char_traits<char>](((std::basic_ostream<char, std::cha r_traits<char> >&)(&std::cout)), ((const char*)"mb1.db1:")) << mb1.multi_bitsets::db1' /usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/bits/ostream.tcc:63: 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/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/bits/ostream.tcc:74: note: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(s td::basic_ios<_CharT, _Traits>&(*)(std::basic_ios<_CharT, _Traits>&)) [with _CharT = char, _Traits = std::char_traits<char>] /usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/bits/ostream.tcc:86: note: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(s td::ios_base&(*)(std::ios_base&)) [with _CharT = char, _Traits = std::char_traits<char>]
And modified code with the initializer list suggested by Cory-san: #include <iostream> #include <boost/timer.hpp> #include <boost/dynamic_bitset.hpp> using namespace std; using namespace boost; struct multi_bitsets{ dynamic_bitset<> db1; dynamic_bitset<> db2; }; multi_bitsets():db1(10,1ul), db2(10,2ul){} int main() { multi_bitsets mb1; cout<<"mb1.db1:"<<mb1.db1<<endl; cout<<"mb1.db2:"<<mb1.db2<<endl; return 0; } Very simple error code: $ g++ multi_bitset_struct.cpp multi_bitset_struct.cpp:14: error: expected unqualified-id before ')' token multi_bitset_struct.cpp:14: error: expected `,' or `;' before ':' token I am very helpful to gett any comments or solution for the error. Very thanks, Fuji