用激发精神中的其他弦代替点燃 [英] Replace lit with different string in boost spirit

问题描述

我正在尝试使用boost spirit解析包含转义序列的带引号的字符串.我正在寻找一种将转义序列 \"替换为相应字符(在这种情况下为" )的方法.到目前为止，我已经提出了这个建议.

I'm trying to parse a quoted string containing escape sequences using boost spirit. I'm looking for a way to replace escape sequences \" with the corresponding character (" in this case). So far I've come up with this.

c_string％= lit('')>> *(lit(" \\\")[push_back(_val，'')]] |(char_-'"'))>>lit('')

替换完成

lit("\\\")[push_back(_val，'"')]

但是，在我看来，这很笨拙且难以理解.有没有更好的方法可以做到这一点?

however this seems to me quite clumsy and unreadable. Is there a better way to accomplish this?

推荐答案

迭代:您可以将"\\\""替换为'\\'>> lit('')，重新格式化一下:

Iterating: you can replace "\\\"" with '\\' >> lit('"'), reformatting a bit:

c_string
    %= lit('"')
    >> *(
           '\\' >> lit('"')[push_back(_val, '"')]
         | (char_ - '"')
    )
    >> lit('"')
    ;

现在，您可以取消某些 lit()调用，因为在Qi域中调用原型表达式时它们是隐式的:

Now, you can do away with some of the lit() calls because they're implicit when invoking proto expressions in the Qi domain:

c_string
    %= '"'
    >> *(
           '\\' >> lit('"')[push_back(_val, '"')]
         | (char_ - '"')
    )
    >> '"'
    ;

接下来， lit(ch)[push_back(_val，ch)] 只是一种笨拙的方式来表达 char_(ch):

Next up, lit(ch)[push_back(_val, ch)] is just a clumsy way to say char_(ch):

c_string = '"'
    >> *( '\\' >> char_('"') | (char_ - '"') )
    >> '"';

请注意，我们现在也没有％= 的麻烦(请参阅)，您可以保留 phoenix.hpp 包含

Note now we don't have the kludge of %= either (see Boost Spirit: "Semantic actions are evil"?) and you can leave the phoenix.hpp include(s)

最后，您可以说出〜char_(xyz):

c_string = '"' >> *('\\' >> char_('"') | ~char_('"')) >> '"';

现在，您实际上并没有在这里解析C样式的字符串.您不处理转义符，为什么不简化:

Now, you're not actually parsing C-style strings here. You're not handling escapes, so why not simplify:

c_string = '"' >> *('\\' >> char_|~char_('"')) >> '"';

请注意，现在您实际上解析了反斜杠转义符，否则就不会解析(您可以将"\\" 解析为"\\" 而不是"\")

如果您想更加精确，请考虑处理转义符，例如在Boost.Spirit中处理utf-8utf-32解析器

If you want to be more precise, consider handling escapes like e.g. Handling utf-8 in Boost.Spirit with utf-32 parser

在Coliru上直播

#include <boost/spirit/include/qi.hpp>
namespace qi = boost::spirit::qi;

int main() {
    const qi::rule<std::string::const_iterator, std::string()> c_string
        = '"' >> *('\\' >> qi::char_|~qi::char_('"')) >> '"';

    for (std::string const input: {
            R"("")"               , // ""
            R"("\"")"             , // "\\\""
            R"("Hello \"world\"")", // "Hello \\\"world\\\""
        })
    {
        std::string output;
        if (parse(input.begin(), input.end(), c_string, output)) {
            std::cout << input << " -> " << output << "\n";
        } else {
            std::cout << "Failed: " << input << "\n";
        }
    }
}

打印

"" -> 
"\"" -> "
"Hello \"world\"" -> Hello "world"

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