使用boost-spirit解析ipv4地址

Question

我想使用boost::spirit来解析ipv4地址。以下是我尝试做的事情：

#include <string>
#include <string.h>
#include <iostream>
#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/phoenix_core.hpp>
#include <boost/spirit/include/phoenix_operator.hpp>

struct Ipv4 { union { uint32_t as_int; uint8_t as_char[4]; } raw; };

Ipv4 make_ipv4(uint8_t i1, uint8_t i2, uint8_t i3, uint8_t i4) {
    Ipv4 ip;
    ip.raw.as_char[0] = i1; ip.raw.as_char[1] = i2;
    ip.raw.as_char[2] = i3; ip.raw.as_char[3] = i4;
    return ip;
}

namespace qi = boost::spirit::qi;
qi::uint_parser<uint8_t, 10, 1, 3> octet;

struct Ipv4Address : qi::grammar<const char *, Ipv4()> {
    Ipv4Address() : Ipv4Address::base_type(start) {
        start = ( octet >> qi::lit('.') >> octet >> qi::lit('.') >>
                  octet >> qi::lit('.') >> octet
                ) [
                    //qi::_val = make_ipv4(1, 2, 3, 4) // working
                    qi::_val = make_ipv4(qi::_1, qi::_2, qi::_3, qi::_4) // compile error
                ]
        ;
    }
    qi::rule<const char *, Ipv4()> start;
} ipv4_address;

int main() {
    Ipv4 ip;
    const char * s = "1.2.3.4";
    bool r = qi::parse(s, s+strlen(s), ipv4_address, ip);
    std::cout << r << " " << (int)ip.raw.as_char[0] << "." <<
                             (int)ip.raw.as_char[1] << "." <<
                             (int)ip.raw.as_char[2] << "." <<
                             (int)ip.raw.as_char[3] << std::endl;
}

编译这段代码时，我得到了以下编译错误：

/tmp/ip.cxx:在构造函数'Ipv4Address::Ipv4Address()'：/tmp/ip.cxx:26:72: error:无法将参数'1‘的'const _1_type {aka const boost::phoenix::actor >}’转换为'uint8_t {aka unsigned char}‘到'Ipv4 make_ipv4(uint8_t，uint8_t)’

有什么提示吗？

这是“正确”的方法吗？

Answer 1

您需要使用bind来延迟绑定语义操作中的函数：

namespace qi = boost::spirit::qi;
namespace phx = boost::phoenix;
qi::uint_parser<uint8_t, 10, 1, 3> octet;

struct Ipv4Address : qi::grammar<const char *, Ipv4()> {
    Ipv4Address() : Ipv4Address::base_type(start) {
        start = ( octet >> qi::lit('.') >> octet >> qi::lit('.') >>
                  octet >> qi::lit('.') >> octet
                ) [
                    qi::_val = phx::bind(make_ipv4, qi::_1, qi::_2, qi::_3, qi::_4)
                ]
        ;
    }
    qi::rule<const char *, Ipv4()> start;
} ipv4_address;

完整示例：

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

struct Ipv4 { union { uint32_t as_int; uint8_t as_char[4]; } raw; };

Ipv4 make_ipv4(uint8_t i1, uint8_t i2, uint8_t i3, uint8_t i4) {
    Ipv4 ip;
    ip.raw.as_char[0] = i1; ip.raw.as_char[1] = i2;
    ip.raw.as_char[2] = i3; ip.raw.as_char[3] = i4;
    return ip;
}

namespace qi = boost::spirit::qi;
namespace phx = boost::phoenix;
qi::uint_parser<uint8_t, 10, 1, 3> octet;

struct Ipv4Address : qi::grammar<const char *, Ipv4()> {
    Ipv4Address() : Ipv4Address::base_type(start) {
        start = ( octet >> qi::lit('.') >> octet >> qi::lit('.') >>
                  octet >> qi::lit('.') >> octet
                ) [
                    qi::_val = phx::bind(make_ipv4, qi::_1, qi::_2, qi::_3, qi::_4)
                ]
        ;
    }
    qi::rule<const char *, Ipv4()> start;
} ipv4_address;

int main() {
    Ipv4 ip;
    const char * s = "1.2.3.4";
    bool r = qi::parse(s, s+strlen(s), ipv4_address, ip);
    std::cout << r << " " << (int)ip.raw.as_char[0] << "." <<
                             (int)ip.raw.as_char[1] << "." <<
                             (int)ip.raw.as_char[2] << "." <<
                             (int)ip.raw.as_char[3] << std::endl;
}