Re: [Boost-users] boost::xpressive : Get thousand separator as double

If performance matters, you might want to avoid xpressive::as. It's just a thin wrapper over boost::lexical_cast, which may(?) do dynamic allocation while performing conversion. Try this, which uses a wrapper over std::atoi instead. (It's a bit sneaky in that it uses the fact that characters in a string are guaranteed contiguous, and that atoi stops parsing on the first non-digit.) Disclaimer: this code is not well-tested. struct asint_ : std::unary_function { int operator()(xp::ssub_match const &s) const { return (int)std::atoi(&*s.first); } }; xp::function::type const asint = {}; int main() { using namespace xp; placeholder<double> result; sregex double_ = ~after(_d) >> // a number with no group separators, and either a period or comma // for fraction separator (+_d)[result = asint(_)] >> !((set=',','.') >> (_d >> _d)[result += asint(_)/100.0]) >> ~before(set[_d|','|'.']) // A number with optional group separators | repeat<1,3>(_d)[result = asint(_)] >> ( // ... with comma group separators and period fraction separator *(',' >> repeat<3>(_d)[result *= 1000, result += asint(_)]) >> !('.' >> (_d >> _d)[result += asint(_)/100.0]) >> ~before(set[_d|','|'.']) // ... with period group separators and comma fraction separator | *('.' >> repeat<3>(_d)[result *= 1000, result += asint(_)]) >> !(',' >> (_d >> _d)[result += asint(_)/100.0]) >> ~before(set[_d|','|'.']) ); std::string str; double d = 0.0; smatch what; what.let(result = d); std::cout << std::fixed << std::setprecision(2); while (std::getline(std::cin, str)) { if (regex_search(str, what, double_)) { std::cout << "Double = " << d << '\n'; } else { std::cout << "No match\n"; } } } On 9/9/2011 5:26 AM, Jens Saathoff wrote:

Perfect! That works!

I will compare it with my thousand-sep rule/grammar in boost::spirit, a little benchmark to find out which one is faster. Do have experiences/results with boost::spirit vs. boost::xpressive?

Thank you very much. Have a nice weekend.

2011/9/9 Eric Niebler mailto:eric@boostpro.com>

#include <string> #include <iostream> #include <iomanip> #include #include namespace xp = boost::xpressive;

int main() { using namespace xp; placeholder<double> result; sregex double_ = ~after(_d) >> // a number with no group separators, and either a period or comma // for fraction separator (+_d)[result = as<double>(_)] >> !((set=',','.') >> (_d >> _d)[result += as<int>(_)/100.0]) >> ~before(set[_d|','|'.']) // A number with optional group separators | repeat<1,3>(_d)[result = as<int>(_)] >> ( // ... with comma group separators and period fraction separator *(',' >> repeat<3>(_d)[result *= 1000, result += as<int>(_)]) >> !('.' >> (_d >> _d)[result += as<int>(_)/100.0]) >> ~before(set[_d|','|'.']) // ... with period group separators and comma fraction separator | *('.' >> repeat<3>(_d)[result *= 1000, result += as<int>(_)]) >> !(',' >> (_d >> _d)[result += as<int>(_)/100.0]) >> ~before(set[_d|','|'.']) );

std::string str; double d = 0.0; smatch what; what.let(result = d); std::cout << std::fixed << std::setprecision(2); while (std::getline(std::cin, str)) { if (regex_search(str, what, double_)) { std::cout << "Double = " << d << '\n'; } else { std::cout << "No match\n"; } } }

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