Respected Sir, I am using boost::circular_buffer in my program. It uses Visual Studio 7.1 . I am facing some problem related to iterator const correctness, where a nonconst iterator can't be converted to const iterator in release mode only (it works fine in debug mode) The program demosntrates it , #include <boost/circular_buffer.hpp> #include <boost/lambda/lambda.hpp> #include <iostream> int main(){ using namespace boost; using namespace boost::lambda; typedef circular_buffer<int> int_buf; int_buf buf(3); buf.push_back(1); buf.push_back(2); buf.push_back(3); buf.push_back(4); int_buf::const_iterator itb = buf.begin(); int_buf::const_iterator ite = buf.end(); std::for_each(itb,ite,std::cout<<_1<<"\t"); } It gives error in release mode of VS 7.1 as, e:\boost\trunk\boost\circular_buffer\details.hpp(262): error C2248: 'boost::cb_details::iterator<Buff,Traits>::m_buff' : cannot access private member declared in class 'boost::cb_details::iterator<Buff,Traits>' with [ Buff=boost::circular_buffer<int>, Traits=boost::cb_details::nonconst_traits<std::allocator<int>> ] and [ Buff=boost::circular_buffer<int>, Traits=boost::cb_details::nonconst_traits<std::allocator<int>> ] The boost version is latest boost svn trunk download. Apparently it seems, a friend declaration is missing, which causes the error in iterator to const iterator conversion through iterator(const nonconst_self& it) constructor conversion , where it tries to access it.m_it private variable. My second question is, is it valid to pass a const & a non const iterator to any function such as std::for_each, where both const iterators are required. If I pass such thing, it gives error as d:\Visual Studio Projects\Test\Test1.cpp(15): error C2782: '_Fn1 std::for_each(_InIt,_InIt,_Fn1)' : template parameter '_InIt' is ambiguous It it a valid error, or it is supposed to convert a non const iterator to const one, and match the template parameter, if it directly doesnt match anyone (as the conversion ctor is not explicit, I expect such automatic conversion is possible). thank you for such a fantastic library . -- Abir Basak, Member IEEE B. Tech , IIT KGP Technology Lead Software Engineer, Read Ink Technologies