Assigning parsers to auto variables
boost-spirit-qi, c++, parsing
Solution
Spirit Parsers are not designed to be used with `auto` in Spirit V2.
This is because the underlying Proto expression templates hold references to the temporaries.
You can use
- `qi::copy()` (existing in the trunk after boost_1_55_0, not in any released version at this time)
- `boost::proto::deep_copy`
- or BOOST_SPIRIT_AUTO (first coined here)
I've written about these things more often on SO: https://stackoverflow.com/search?q=user%3A85371+deep_copy, specifically, this:
- boost spirit V2 qi bug associated with optimization level
Boost Spirit X3 will not have this limitation.
Problem
Are spirit parsers not meant to be used with `auto`? A simple parser works fine when passed to `qi::parse()` inline, but crashes with segfault if passed via an `auto` variable: ``` #include <cstdio> #include <string> #include <boost/spirit/include/qi.hpp> using namespace std; namespace qi = boost::spirit::qi; int main() { string line = "[z]"; auto bracketed_z = '[' >> +qi::char_('z') >> ']'; auto p = line.cbegin(); printf("%d", qi::parse(p, line.cend(), '[' >> +qi::char_('z') >> ']')); // Works p = line.cbegin(); printf("%d", qi::parse(p, line.cend(), bracketed_z)); // Crashes } ``` Reproes with g++-4.8 and VC13. Update: an error was fixed in the original code (`p` was not re-initialized before the second call to `parse()`).