Boost already has a library for that problem: Spirit. With Spirit2, in fact, my understanding is that it has a consistent way to both directions as well. (Arguably serialization does as well, but there any parsing is an implementation detail.)
I am glad you brought it up. Something along these lines was nagging me as I was using boost::serialization for ultimately conversion to/from XML (i.e. string) and Hartmut mentioned Spirit capable of doing conversions. So, I was wondering if that my noise about conversion was not mis-guided. I played with Spirit (the parser part) only a little bit. I only managed to write a half-a-page parsing grammar just to happily replace it with a two-liner regular expression. Never looked back.
Could you show how to convert int-to-string-to-int with Spirit? Can we apply hex/scientific/etc. formatting? Does it deal with user types (as lexical_cast does)?
namespace qi = boost::spirit::qi; namespace karma = boost::spirit::karma; int i = 0; if (qi::parse("1", int_, i)) karma::generate(outiter, int_, i); where outiter is some output iterator. 'int_' is only one of the available primitives, there are more: uint, long_, ulong, double_, float_, you get the picture. Full customization for special formats is provided, just write your own policies. Example: template <typename T> struct scientific_policy : karma::real_generator_policies<T> { // we want the numbers always to be in scientific format typedef karma::real_generator_policies<T> base_type; static int floatfield(T) { return base_type::scientific; } }; typedef karma::real_spec<double, scientific_policy<double> > science_type; double d = 1.2345; karma::generate(outiter, science_type(), d); which will generate: "1.234e00" (the default number of fractional digits is 3, but this can be changed easily as well). etc. the parse/generate functions are just one possible interface, another is to use iostream base manipulators: int i = 0; std::ci >> qi::match(int_, i); std::cout << karma::format(int_, i) << std::endl; HTH Regards Hartmut