Using Boost.Spirit to extract certain tags/attributes from HTML http://stackoverflow.com/questions/8501935/using-boost-spirit-to-extract-certain-tags-attributes-from-html

expressive.cpp

#include <string>
#include <iostream>
#include <boost/xpressive/xpressive.hpp>

void handle_attr(
        const std::string& elem, 
        const std::string& attr, 
        const std::string& value)
{
    if (elem == "img" && attr == "src")
        std::cout << "value : " << value << std::endl;
}

typedef std::string::const_iterator It;

int main(int argc, const char *argv[])
{
    using namespace boost::xpressive;
#if DYNAMIC
    const sregex re = sregex::compile("<img\\s+[^\\>]*?src\\s*=\\s*([\"'])(.*?)\\1");
#else
    const sregex re = "<img" >> +_s >> -*(~(set = '\\','>')) >> 
        "src" >> *_s >> '=' >> *_s
        >> (s1 = as_xpr('"') | '\'') >> (s2 = -*_) >> s1;
#endif

    std::string s;
    smatch what;

    while (std::getline(std::cin, s))
    {
        It f = s.begin(), l = s.end();

        do
        {
            if (!regex_search(f, l, what, re))
                break;

            handle_attr("img", "src", what[2]);
            f = what[0].second;
        } while (f!=s.end());
    }
    
    return 0;
}

Makefile

all: spirit regex expressive

#CPPFLAGS+=-std=c++0x
CPPFLAGS+=-g -O3
CPPFLAGS+=-I /home/sehe/custom/boost_1_48_0
CPPFLAGS+=-L /home/sehe/custom/boost_1_48_0/stage/lib/
LDFLAGS+=-lboost_regex
CPPFLAGS+=-Wall

%:%.cpp
	g++ $(CPPFLAGS) $^ -o $@ $(LDFLAGS)

regex.cpp

#include <string>
#include <iostream>
#include <boost/regex.hpp>

void handle_attr(
        const std::string& elem, 
        const std::string& attr, 
        const std::string& value)
{
    if (elem == "img" && attr == "src")
        std::cout << "value : " << value << std::endl;
}

typedef std::string::const_iterator It;

int main(int argc, const char *argv[])
{
    const boost::regex re("<img\\s+[^\\>]*?src\\s*=\\s*([\"'])(.*?)\\1");

    std::string s;
    boost::smatch what;

    while (std::getline(std::cin, s))
    {
        It f = s.begin(), l = s.end();

        do
        {
            if (!boost::regex_search(f, l, what, re))
                break;

            handle_attr("img", "src", what[2]);
            f = what[0].second;
        } while (f!=s.end());
    }
    
    return 0;
}

spirit.cpp

//#define BOOST_SPIRIT_DEBUG
#include <string>
#include <iostream>
#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/phoenix.hpp>

namespace qi  = boost::spirit::qi;
namespace phx = boost::phoenix;

void handle_attr(
        const std::string& elem, 
        const std::string& attr, 
        const std::string& value)
{
    if (elem == "img" && attr == "src")
        std::cout << "value : " << value << std::endl;
}

typedef std::string::const_iterator It;
typedef qi::space_type Skipper;

struct grammar : qi::grammar<It, Skipper>
{
    grammar() : grammar::base_type(html)
    {
        using namespace boost::spirit::qi;
        using phx::bind;

        attr = as_string [ +~char_("= \t\r\n/>") ] [ _a = _1 ]
                >> '=' >> (
                    as_string [ '"' >> lexeme [ *~char_('"') ] >> '"' ]
                  | as_string [ "'" >> lexeme [ *~char_("'") ] >> "'" ]
                  ) [ boost::phoenix::bind(handle_attr, _r1, _a, _1) ]
            ;

        elem = lit('<') 
            >> as_string [ lexeme [ ~char_("-/>") >> *(char_ - space - char_("/>")) ] ] [ _a = _1 ]
            >> *attr(_a);

        html = (-elem) % +("</" | (char_ - '<'));

        BOOST_SPIRIT_DEBUG_NODE(html);
        BOOST_SPIRIT_DEBUG_NODE(elem);
        BOOST_SPIRIT_DEBUG_NODE(attr);
    }

    qi::rule<It, Skipper> html;
    qi::rule<It, Skipper, qi::locals<std::string> > elem;
    qi::rule<It, qi::unused_type(std::string), Skipper, qi::locals<std::string> > attr;
};

int main(int argc, const char *argv[])
{
    std::string s;

    const static grammar html_;

    while (std::getline(std::cin, s))
    {
        It f = s.begin(),
           l = s.end();

        if (!phrase_parse(f, l, html_, qi::space) || (f!=l))
            std::cerr << "unparsed: " << std::string(f,l) << std::endl;
    }
    
    return 0;
}