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I have to parse a string that can optionally have square brackets in it. For e.g. This can be my token string:

xyz[aa:bb]:blah

I have used rules like

  • +(~qi::char_("\r\n;,="))
  • +(~qi::char_("\r\n;,=") | "[" | "]")
  • +(qi::char_ - qi::char_("\r\n;,="))

But none of them accepts the square brackets. Is there some special handling of [] in the parser?

Paani
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1 Answers1

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You need to show the code. Here's a simple tester that shows that all of the parsers succeed and give the expected result:

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#include <boost/spirit/include/qi.hpp>
#include <iomanip>

namespace qi = boost::spirit::qi;

int main()
{
    using It = std::string::const_iterator;

    for(std::string const input : {"xyz[aa:bb]:blah"})
    {
        qi::rule<It, std::string()> rules[] = {
            +(~qi::char_("\r\n;,=")),
            +(~qi::char_("\r\n;,=") | "[" | "]"),
            +(qi::char_ - qi::char_("\r\n;,=")),
        };
        for(auto const& r : rules)
        {
            std::string out;
            std::cout << std::boolalpha
                      << qi::parse(begin(input), end(input), r, out) << " -> "
                      << std::quoted(out) << "\n";
        }
    }
}

Printing:

true -> "xyz[aa:bb]:blah"
true -> "xyz[aa:bb]:blah"
true -> "xyz[aa:bb]:blah"

The best guesses I have, not seeing your actual code:

  • you are using a skipper that eats some of your characters (see Boost spirit skipper issues)

  • you are using an input iterator that interferes

  • you're invoking UB. To be honest, without context, this seems the most likely

If you show more code I'll happily diagnose which it is.

sehe
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  • you right. That does work. Figured out that in my complex grammar it was another segment that was causing the issue. Somehow, my memory tricked me into doubting the wrong part as I have faced skipper issues in the past around this. Thanks for your help :-) – Paani Jun 20 '22 at 11:22