解析结尾带有值修饰符('-'，'％')的字符串 [英] parsing strings with value modifiers ('-', '%') at the end
问题描述
我尝试着解析.
我有一些de-de格式的数据，在字符串的末尾有其他信息.
I have some data that comes in a de-de format with additional information at the end of the string.
我设法正确定义了de-de部分，但是我在正确解析-和%方面遇到了困难.我阅读了codecvt的内容，但不理解该主题.
I managed to get the de-de part correct but I struggle in getting the - and % parsed correctly. I read up on codecvt but I do not understand the topic.
以下是我到目前为止所了解的内容以及我需要做的事的示例.
Here is a reflection of what I understand so far and an example of what I need to do.
#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
}
输出为:
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
我如何灌流，以便像我需要的那样读取-和%符号?
How can I imbue my stream so that it reads the - and % sign like I need it to?
推荐答案
我将直接解决这个问题:让我们在这里开始解析.
I'd tackle this head-on: let's get to grips with parsing here.
无论如何，您最终都将其写在某个地方，所以我忘了先创建一个(昂贵的)字符串流的必要.
You'd end up writing that somewhere anyways, so I'd forget about the need to create an (expensive) string stream first.
选择武器:增强精神
注意，
-
我直接使用迭代器来解析字符串.我的代码很漂亮 关于所使用的浮点数类型的通用.
I parse the string using it's iterators directly. My code is pretty generic as to the type of floating point number used.
您几乎可以用以下方式搜索替换double:
boost::multiprecision::cpp_dec_float(或将其设为模板
参数)并进行解析.因为我预测您需要解析器
十进制浮点数，而不是二进制浮点数.您在转换中失去了准确性.
You can pretty much search replace double by e.g.
boost::multiprecision::cpp_dec_float (or make it a template
argument) and be parsing. Because I predict that you needed to parser
decimal floating point numbers, not binary floating point numbers. You're losing accuracy in the conversion.
简单语法
从本质上讲，语法非常简单:
The Simple Grammar
At it's core, the grammar is really simple:
if (parse(numstr.begin(), numstr.end(), mynum >> matches['-'] >> matches['%'],
value, sign, pct))
{
if (sign) value = -value;
if (pct) value /= 100;
return value;
}
那里有.当然，我们需要定义mynum，以便它按预期解析 unsigned 实数:
There you have it. Of couse, we need to define mynum so it parses the unsigned real numbers as expected:
using namespace qi;
real_parser<double, de_numpolicy<double> > mynum;
魔法:real_policies<>
The Magic: real_policies<>
The documentation goes a long way to explaining how to tweak real number parsing using real_policies. Here's the policy I came up with:
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
#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，则会显示:
If you uncomment the "DEBUG" line, it prints:
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)
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