解析末尾带有值修饰符（'-'、'%'）的字符串

我尝试着去掌握解析。

我有一些数据来自de-de格式在字符串末尾带有附加信息。

我设法使 de-de 部分正确，但我很难得到- and %解析正确。我读了codecvt但我不明白这个话题。

这是我迄今为止所理解的反映以及我需要做的事情的示例。

#include <string>
#include <locale>
#include <iostream>
#include <sstream>

using namespace std;

#define EXPECT_EQ(actual, expected) { \
    if (actual != expected) \
    { \
        cout << "expected " << #actual << " to be " << expected << " but was " << actual << endl; \
    } \
}

double parse(wstring numstr)
{
    double value;
    wstringstream is(numstr);
    is.imbue(locale("de-de"));
    is >> value;
    return value;
}

int main()
{
    EXPECT_EQ(parse(L"123"), 123); //ok
    EXPECT_EQ(parse(L"123,45"), 123.45); //ok
    EXPECT_EQ(parse(L"1.000,45"), 1000.45); //ok
    EXPECT_EQ(parse(L"2,390%"), 0.0239); //% sign at the end
    EXPECT_EQ(parse(L"1.234,56-"), -1234.56); //- sign at the end
}

输出是：

expected parse(L"2,390%") to be 0.0239 but was 2.39
expected parse(L"1.234,56-") to be -1234.56 but was 1234.56

我怎样才能注入我的流，以便它读取- and %像我需要的那样签名？

我会正面解决这个问题：让我们在这里开始解析。

无论如何，你最终都会在某个地方写下它，所以我会忘记首先需要创建一个（昂贵的）字符串流。

选择的武器：提升精神

Note,

• 我直接使用它的迭代器解析字符串。我的代码很漂亮 关于所使用的浮点数的类型的通用。

• 您几乎可以搜索替换double例如boost::multiprecision::cpp_dec_float（或者将其作为模板 参数）并进行解析。因为我预测你需要解析decimal浮点数，不是binary浮点数字。您会失去转换的准确性。

UPDATE: 扩展样本住在科里鲁 http://coliru.stacked-crooked.com/a/61512abc5396630d

简单语法

从本质上讲，语法非常简单：

if (parse(numstr.begin(), numstr.end(), mynum >> matches['-'] >> matches['%'],
            value, sign, pct)) 
{
    if (sign) value = -value;
    if (pct)  value /= 100;

    return value;
}

你有它。当然，我们需要定义mynum所以它解析unsigned如预期的实数：

using namespace qi;
real_parser<double, de_numpolicy<double> > mynum;

魔术：real_policies<>

该文档详细解释了如何使用调整实数解析real_policies http://www.boost.org/doc/libs/1_59_0/libs/spirit/doc/html/spirit/qi/reference/numeric/real.html#spirit.qi.reference.numeric.real._code__phrase_role__identifier__realpolicies__phrase___code_。这是我想出的政策：

template <typename T>
    struct de_numpolicy : qi::ureal_policies<T>
{
    //  No exponent
    template <typename It>                static bool parse_exp(It&, It const&)          { return false; } 
    template <typename It, typename Attr> static bool parse_exp_n(It&, It const&, Attr&) { return false; } 

    //  Thousands separated numbers
    template <typename It, typename Attr>
    static bool parse_n(It& first, It const& last, Attr& attr)
    {
        qi::uint_parser<unsigned, 10, 1, 3> uint3;
        qi::uint_parser<unsigned, 10, 3, 3> uint3_3;

        if (parse(first, last, uint3, attr)) {
            for (T n; qi::parse(first, last, '.' >> uint3_3, n);)
                attr = attr * 1000 + n;

            return true;
        }

        return false;
    }

    template <typename It>
        static bool parse_dot(It& first, It const& last) {
            if (first == last || *first != ',')
                return false;
            ++first;
            return true;
        }
};

完整演示

Live On Coliru http://coliru.stacked-crooked.com/a/50416c7060695ab5

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


#define EXPECT_EQ(actual, expected) { \
    double v = (actual); \
    if (v != expected) \
    { \
        std::cout << "expected " << #actual << " to be " << expected << " but was " << v << std::endl; \
    } \
}

namespace mylib {
    namespace qi = boost::spirit::qi;

    template <typename T>
        struct de_numpolicy : qi::ureal_policies<T>
    {
        //  No exponent
        template <typename It>                static bool parse_exp(It&, It const&)          { return false; } 
        template <typename It, typename Attr> static bool parse_exp_n(It&, It const&, Attr&) { return false; } 

        //  Thousands separated numbers
        template <typename It, typename Attr>
        static bool parse_n(It& first, It const& last, Attr& attr)
        {
            qi::uint_parser<unsigned, 10, 1, 3> uint3;
            qi::uint_parser<unsigned, 10, 3, 3> uint3_3;

            if (parse(first, last, uint3, attr)) {
                for (T n; qi::parse(first, last, '.' >> uint3_3, n);)
                    attr = attr * 1000 + n;

                return true;
            }

            return false;
        }

        template <typename It>
            static bool parse_dot(It& first, It const& last) {
                if (first == last || *first != ',')
                    return false;
                ++first;
                return true;
            }
    };

    template<typename Char, typename CharT, typename Alloc>
    double parse(std::basic_string<Char, CharT, Alloc> const& numstr)
    {
        using namespace qi;
        real_parser<double, de_numpolicy<double> > mynum;

        double value;
        bool sign, pct;

        if (parse(numstr.begin(), numstr.end(), mynum >> matches['-'] >> matches['%'],
                    value, sign, pct)) 
        {
            // std::cout << "DEBUG: " << std::boolalpha << " '" << numstr << "' -> (" << value << ", " << sign << ", " << pct << ")\n";
            if (sign) value = -value;
            if (pct)  value /= 100;

            return value;
        }

        assert(false); // TODO handle errors
    }

} // namespace mylib

int main()
{
    EXPECT_EQ(mylib::parse(std::string("123")),       123);      // ok
    EXPECT_EQ(mylib::parse(std::string("123,45")),    123.45);   // ok
    EXPECT_EQ(mylib::parse(std::string("1.000,45")),  1000.45);  // ok
    EXPECT_EQ(mylib::parse(std::string("2,390%")),    0.0239);   // %  sign at the end
    EXPECT_EQ(mylib::parse(std::string("1.234,56-")), -1234.56); // -  sign at the end
}

如果取消注释“DEBUG”行，它将打印：

DEBUG:  '123' -> (123, false, false)
DEBUG:  '123,45' -> (123.45, false, false)
DEBUG:  '1.000,45' -> (1000.45, false, false)
DEBUG:  '2,390%' -> (2.39, false, true)
DEBUG:  '1.234,56-' -> (1234.56, true, false)