Hi Vladimir, While reading the Boost.Convert documentation last night there were some questions which came to my mind: Have you considered using iterators (or ranges) to specify input? Would that be in the scope of your library? Also I note that the strtol() function returns the position of the first invalid character (endptr below): long int strtol (const char* str, char** endptr, int base); Could convert() provide the position where the conversion stopped? This would allow single pass parsing of some input data. Would a Converter callable with the following signature be useful? template<typename TypeOut, typename InputIterator> class Result { public: enum Errc { numeric_overflow, empty_range, invalid_character, ...}; // std::expected like function signatures here private: TypeOut value; int errors; InputIterator pos; }; template<typename TypeOut, typename InputIterator> void operator()(InputIterator begin, InputIterator end, Result<TypeOut, InputIterator>& result) const; Please let me know your thoughts. Thanks, Marius Dobrea