Hello, Since introduction of VC 8, boost::format causes an assertion failure, if empty strings are provided as format arguments, e.g. std::string arg; boost::format frmt("%s"); // Alternatively use: "%1%" std::string res = (frmt % arg).str(); This defect is well known since end of 2005 (e.g. by Mick Hollins et al. in the thread "[Boost.Format] empty string argument causes VC 8.0 to assert" or by J.S.Otis in the thread "Assertion failure usign boost::format with Visual C++ 2005" The defect was well-analyzed by Caleb Epstein and I share his opinion, that this is due to a defect in boost::io::detail::mk_str, which provides a null pointer as argument to std::string::append, which violates its preconditions. The null pointer effectively is a result of some streambuf::pbase() call, which is allowed to return a null result under well-defined conditions. My question is: Has this error been fixed since then? Thanks in advance, Daniel Krügler