How to parse an 8-bit hexadecimal number and a string using boost C++?

Question

I have just started using boost C++ libraries for some parser work. I would like to use some help on the following:

1. Matching an 8-bit hexadecimal number. I have tried: char_("0-9a-fA-F") which matches only one hexadecimal digit. I've also tried using: *char_("0-9a-fA-F"), but it is also not working

2. Matching any string with underscore characters? For example, aBCd_Efgh

Answer 1

Since indeed char_ is from boost::spirit::qi you'll want to simply use the integer parser:

• http://www.boost.org/doc/libs/1_55_0/libs/spirit/doc/html/spirit/qi/reference/numeric/int.html

This is easily used to parse hexadecimals:

qi::int_parser<unsigned char, 16, 2, 2> hex_byte;

will match and parse exactly 2 hexadecimal digits in succession.

Answer 2

If you are using PCRE, i.e., initialized your regex like boost::regex e1(my_expression) or boost::regex e2(my_expression, boost::regex::perl), then:

1. You can specify a quantifier using brackets ({min,max}), so a{3,10} would match 3 to 10 a characters. You can apply that to a group, like [0-9a-fA-F]{1,2}
2. A group expression would do fine: [0-9a-zA-Z_]+

If you are using POSIX, the differences are:

1. You need to escape the brackets \{min,max\}
2. Nothing.