Question

我试图使用real_parser和以下ureal_policies解析实数：

template <typename T>
struct number_real_policies : qi::ureal_policies<T>
{
    static bool const expect_dot = true;

    template <typename Iterator, typename Attribute>
    static bool
    parse_nan(Iterator& first, Iterator const& last, Attribute& attr) {
        return false;
    }

    template <typename Iterator, typename Attribute>
    static bool
    parse_inf(Iterator& first, Iterator const& last, Attribute& attr) {
        return false;
    }
};

它似乎完美地解析了我需要的实数格式的所有变体，但我注意到以下字符串也被接受：“。12345.e12”。

在小数部分接受两个点是否正常（它只适用于E / e之前的第二个点，并且E / e必须存在）？

提前致谢

Answer 1

正如@llonesmiz在我的测试应用程序中正确指出的那样，它完全按照设计工作：

<强> Live On Coliru

您好像忘记检查解析器退出代码？

#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/karma.hpp>

namespace qi    = boost::spirit::qi;
namespace karma = boost::spirit::karma;

typedef std::vector<double> attr_t;

template <typename T>
struct number_real_policies : qi::ureal_policies<T>
{
    static bool const expect_dot = true;

    template <typename Iterator, typename Attribute>
    static bool
    parse_nan(Iterator& first, Iterator const& last, Attribute& attr) {
        return false;
    }

    template <typename Iterator, typename Attribute>
    static bool
    parse_inf(Iterator& first, Iterator const& last, Attribute& attr) {
        return false;
    }
};

template <typename It, typename Skipper = qi::space_type>
    struct parser : qi::grammar<It, attr_t(), Skipper>
{
    parser() : parser::base_type(start)
    {
        using namespace qi;

        start %= *mydouble_;
        BOOST_SPIRIT_DEBUG_NODE(start);
    }

  private:
    qi::rule<It, attr_t(), Skipper> start;
    qi::real_parser<double, number_real_policies<double> > mydouble_;
};

bool doParse(const std::string& input)
{
    typedef std::string::const_iterator It;
    auto f(begin(input)), l(end(input));

    parser<It, qi::space_type> p;
    attr_t data;

    try
    {
        bool ok = qi::phrase_parse(f,l,p,qi::space,data);
        if (ok)   
        {
            std::cout << "parse success\n";
            std::cout << "data: " << 
                karma::format_delimited(karma::columns(3) [*karma::auto_], ' ', data) << "\n";
        }
        else      std::cerr << "parse failed: '" << std::string(f,l) << "'\n";

        if (f!=l) std::cerr << "trailing unparsed: '" << std::string(f,l) << "'\n";
        return ok;
    } catch(const qi::expectation_failure<It>& e)
    {
        std::string frag(e.first, e.last);
        std::cerr << e.what() << "'" << frag << "'\n";
    }

    return false;
}

int main()
{

    bool ok = doParse(
            "0.    2.    .3    \n  "
            "0.e7  2.e7  .3e7  \n"
            "0.e-7 2.e-7 .3e-7 \n"
            // shouldn't accept:
            //"0..e7\n"
            "0.3.e7\n"
            );
    return ok? 0 : 255;
}

输出：

parse success
data: 0.0 2.0 0.3 
0.0 2.0e07 3.0e06 
0.0 2.0e-07 3.0e-08 
0.3 

trailing unparsed: '.e7
'

精神real_parser“.e”

1 个答案: