boost spirit qi - 将字符串解析为布尔值

boost spirit qi - parse string into boolean

我需要将字符串解析为布尔值;特别是

请注意,我不想使用函数 qi::parse 的 return 值;我想要 qi::parse 函数设置一个布尔变量作为参数。类似于以下(未编译)代码:

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

using namespace boost::spirit;

int main() {
    bool b;
    std::string s("ack");
    auto it = s.begin();
    if (qi::parse(it, s.end(), < need a rule here... >, b))
        std::cout << "Value: " << std::boolalpha << b << std::endl;
    return 0;
}

非常感谢。

想到的最简单的方法是 "noack" >> qi::attr(false) 及其补充。添加 eoi 以确保解析完整输入:

Live On Coliru

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

namespace qi = boost::spirit::qi;

int main() {
    for (std::string const s : {"ack","noack","oops","ack 2",""}) {
        bool b;
        if (qi::parse(s.begin(), s.end(), ("ack" >> qi::attr(true) | "noack" >> qi::attr(false)) >> qi::eoi, b))
            std::cout << "'" << s << "' -> " << std::boolalpha << b << std::endl;
        else
            std::cout << "'" << s << "' -> FAIL\n";
    }
}

版画

'ack' -> true
'noack' -> false
'oops' -> FAIL
'ack 2' -> FAIL
'' -> FAIL

奖金:

使用symbol更优雅:

Live On Coliru

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

namespace qi = boost::spirit::qi;

struct acknoack_type : qi::symbols<char, bool> {
    acknoack_type() { this->add("ack", true)("noack", false); }
} static const acknoack;

int main() {
    for (std::string const s : {"ack","noack","oops","ack 2",""}) {
        bool b;
        if (qi::parse(s.begin(), s.end(), acknoack >> qi::eoi, b))
            std::cout << "'" << s << "' -> " << std::boolalpha << b << std::endl;
        else
            std::cout << "'" << s << "' -> FAIL\n";
    }
}