#include<vector>
#include<boost/spirit/include/qi.hpp>
namespace sqi = boost::spirit::qi;
int main(){
        std::string const v_str = "AA BB CC";
        std::vector<std::string> v;
        auto it = begin(v_str);
        bool r = sqi::phrase_parse(it, end(v_str), (*sqi::lexeme[+sqi::char_("A-Z")]), sqi::space, v);
        assert( v.size() == 3  and v[2] == "CC" );
}

std::string const v_str = "3 AA BB CC";
        std::vector<std::string> v;
        auto it = begin(v_str);
        bool r = sqi::phrase_parse(it, end(v_str), sqi::int_[([&](int i){v.reserve(i);})] >> (*sqi::lexeme[+sqi::char_("A-Z")]), sqi::space, v);