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So far, we've been using the syntax:
double_ >> *(',' >> double_)
to parse a comma-delimited list of numbers. Such lists are common in parsing and Spirit provides a simpler shortcut for them. The expression above can be simplified to:
double_ % ','
read as: a list of doubles separated by ','
.
This sample, again a variation of our previous example, demonstrates just that:
template <typename Iterator> bool parse_numbers(Iterator first, Iterator last, std::vector<double>& v) { using x3::double_; using x3::phrase_parse; using x3::_attr; using ascii::space; auto push_back = [&](auto& ctx){ v.push_back(_attr(ctx)); }; bool r = phrase_parse(first, last, // Begin grammar ( double_[push_back] % ',' ) , // End grammar space); if (first != last) // fail if we did not get a full match return false; return r; }
The full cpp file for this example can be found here: num_list3.cpp