c++ - Parsing escaped strings with boost spirit

Question

I′m working with Spirit 2.4 and I'd want to parse a structure like this:

Text{text_field};

The point is that in text_field is a escaped string with the symbols '{', '}' and ''. I would like to create a parser for this using qi. I've been trying this:

using boost::spirit::standard::char_;
using boost::spirit::standard::string;
using qi::lexeme;
using qi::lit;

qi::rule< IteratorT, std::string(), ascii::space_type > text;
qi::rule< IteratorT, std::string(), ascii::space_type > content;
qi::rule< IteratorT, std::string(), ascii::space_type > escChar;


text %= 
  lit( "Text" ) >> '{' >>
    content >>
  "};"
  ;

content %= lexeme[ +( +(char_ - ( lit( '\' ) | '}' ) )  >> escChar ) ];

escChar %= string( "" ) 
  | string( "\{" ) 
  | string( "\}" );

But doesn't even compile. Any idea?

Answer 1

Your grammar could be written as:

qi::rule< IteratorT, std::string(), ascii::space_type > text; 
qi::rule< IteratorT, std::string() > content;   
qi::rule< IteratorT, char() > escChar;   

text = "Text{" >> content >> "};";  
content = +(~char_('}') | escChar); 
escChar = '\' >> char_("\{}");

i.e.

• text is Text{ followed by content followed by }

• content is at least one instance of either a character (but no }) or an escChar

• escChar is a single escaped \, {, or }

Note, the escChar rule now returns a single character and discards the escaping \. I'm not sure if that's what you need. Additionally, I removed the skipper for the content and escChar rules, which allows to leave off the lexeme[] (a rule without skipper acts like an implicit lexeme).