解析int或double使用boost精神(longest_d) [英] Parse int or double using boost spirit (longest_d)
问题描述
我正在寻找一种方法来解析字符串为int或双,分析器应该尝试两种选择,选择一个相匹配的输入流中最长的部分。
I'm looking for a way to parse a string as an int or a double, the parser should try both alternatives and choose the one matching the longest portion of the input stream.
有一个去precated指令(longest_d)这不正是我要找的:
There is a deprecated directive (longest_d) that does exactly what I'm looking for:
number = longest_d[ integer | real ];
...因为它是德precated,还有其他的选择吗?如果有必要实现语义动作来实现所期望的行为,没有任何人有一个建议?
...since it's deprecated, there are any other alternatives? In case it's necessary to implement a semantic action to achieve the desired behavior, does anyone have a suggestion?
推荐答案
首先,请切换到精神V2 - 这已经取代了的经典的精神,多年来
Firstly, do switch to Spirit V2 - which has superseded classical spirit for years now.
其次,你需要确保一个int获取preferred。默认情况下,双可以解析任意整数同样出色,所以你需要使用 strict_real_policies
而不是:
Second, you need to make sure an int gets preferred. By default, a double can parse any integer equally well, so you need to use strict_real_policies
instead:
real_parser<double, strict_real_policies<double>> strict_double;
现在你可以简单地说明
number = strict_double | int_;
请参阅
- realpolicies documentation
请参阅测试程序的 住在Coliru
See test program Live on Coliru
#include <boost/spirit/include/qi.hpp>
using namespace boost::spirit::qi;
using A = boost::variant<int, double>;
static real_parser<double, strict_real_policies<double>> const strict_double;
A parse(std::string const& s)
{
typedef std::string::const_iterator It;
It f(begin(s)), l(end(s));
static rule<It, A()> const p = strict_double | int_;
A a;
assert(parse(f,l,p,a));
return a;
}
int main()
{
assert(0 == parse("42").which());
assert(0 == parse("-42").which());
assert(0 == parse("+42").which());
assert(1 == parse("42.").which());
assert(1 == parse("0.").which());
assert(1 == parse(".0").which());
assert(1 == parse("0.0").which());
assert(1 == parse("1e1").which());
assert(1 == parse("1e+1").which());
assert(1 == parse("1e-1").which());
assert(1 == parse("-1e1").which());
assert(1 == parse("-1e+1").which());
assert(1 == parse("-1e-1").which());
}
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