small cpp string parser based on boost::spirit

main.cpp

#include <string>
#include <vector>
#include <boost/optional.hpp>
#include <boost/optional/optional_io.hpp>
#include <boost/spirit/include/qi.hpp>

namespace qi = boost::spirit::qi;

template<char Delimiter = ' ', typename... Args>
bool sscanfpp(std::string const &input, Args &...args)
{
	std::vector<std::string> params;
	if (!qi::parse(input.begin(), input.end(),
		+~qi::char_(Delimiter) % Delimiter,
		params))
	{
		return false;
	}

	return sscanfpp_parse(params, std::forward<Args&>(args)...);
}

bool sscanfpp_parse(std::vector<std::string> &params)
{
	return params.size() == 0;
}

// int overload
template<typename... Args>
bool sscanfpp_parse(std::vector<std::string> &params, int &arg, Args& ...args)
{
	std::string const &param = params.front();
	bool res = qi::parse(param.begin(), param.end(), qi::int_, arg);
	params.erase(params.begin());
	return res && sscanfpp_parse(params, std::forward<Args&>(args)...);
}

// float overload
template<typename... Args>
bool sscanfpp_parse(std::vector<std::string> &params, float &arg, Args& ...args)
{
	std::string const &param = params.front();
	bool res = qi::parse(param.begin(), param.end(), qi::float_, arg);
	params.erase(params.begin());
	return res && sscanfpp_parse(params, std::forward<Args&>(args)...);
}

// string overload
template<typename... Args>
bool sscanfpp_parse(std::vector<std::string> &params, std::string &arg, Args& ...args)
{
	std::string const &param = params.front();

	//number as first char is not allowed to distinguish string from int/float
	bool res = qi::parse(param.begin(), param.end(), qi::alpha >> *qi::char_, arg); 

	params.erase(params.begin());
	return sscanfpp_parse(params, std::forward<Args&>(args)...);
}

// optional int overload
template<typename... Args>
bool sscanfpp_parse(std::vector<std::string> &params, boost::optional<int> &arg, Args& ...args)
{
	std::string const &param = params.front();
	bool res = qi::parse(param.begin(), param.end(), -qi::int_, arg);
	if (arg)
		params.erase(params.begin());
	return sscanfpp_parse(params, std::forward<Args&>(args)...);
}

// optional string overload
template<typename... Args>
bool sscanfpp_parse(std::vector<std::string> &params, boost::optional<std::string> &arg, Args& ...args)
{
	std::string const &param = params.front();

	//number as first char is not allowed to distinguish string from int/float
	bool res = qi::parse(param.begin(), param.end(), -(qi::alpha >> *qi::char_), arg);

	if (arg)
		params.erase(params.begin());

	return sscanfpp_parse(params, std::forward<Args&>(args)...);
}

int main()
{
	std::string const input{ "text 123 32.2421" };
	
	std::string text1;
	boost::optional<std::string> text2;
	int number = -1;
	float flt = -1.f;

	bool res = sscanfpp(input, text1, number, text2, flt);

	std::cout << "result: " << res << std::endl;
	std::cout << "text1: " << text1 << std::endl;
	std::cout << "text2: " << text2 << std::endl;
	std::cout << "number: " << number << std::endl;
	std::cout << "float: " << flt << std::endl;
	
	std::cin.get();
	return 0;
}