精神X3不抛出期望失败

Question

从文档中说，当我使用 expect 运算符时，当运算符不匹配时，我应该得到一个expectation_failure。我想捕获异常以指示用户错误输入的位置。但似乎我得到了某种包装的异常：

 terminate called after throwing an instance of 'boost::exception_detail::clone_impl<boost::exception_detail::error_info_injector<boost::spirit::x3::expectation_failure<__gnu_cxx::__normal_iterator<char*, std::string> > > >'
  what():  boost::spirit::x3::expectation_failure
Aborted

我的捕获语句是：

try {
    r = parse(iter, end, wctl_parser::entry, root);
} catch (x3::expectation_failure<char const*> const& x) {
    std::cout << "Never runs,";
} catch (x3::expectation_failure<std::string::const_iterator> const& e) {
    std::cout << "me neither" << std::endl;
}

更新：这是一个展示该行为的小程序：

#include <boost/config/warning_disable.hpp>
#include <boost/spirit/home/x3.hpp>
#include <boost/spirit/home/x3/support/ast/variant.hpp>
#include <boost/spirit/include/qi_char_class.hpp>
#include <boost/fusion/include/adapt_struct.hpp>
#include <iostream>
#include <string>
#include <vector>
namespace wccs_parser {
namespace x3 = boost::spirit::x3;
namespace ascii = x3::ascii;
namespace qi = boost::spirit::qi;
struct AstNullProcess;
struct AstChoiceProcess;
using AstAnyProcess = x3::variant<
     x3::forward_ast<AstNullProcess>,
     x3::forward_ast<AstChoiceProcess>
>;
struct AstNullProcess {};
struct AstChoiceProcess {
    AstAnyProcess left;
    AstAnyProcess right;
};

} // End namespace
BOOST_FUSION_ADAPT_STRUCT(wccs_parser::AstChoiceProcess, left, right)
namespace wccs_parser {
template <typename T> auto rule = [](const char* name = typeid(T).name()) {
     struct _{};
     return x3::rule<_, T> {name};
};
template <typename T> auto as = [](auto p) { return rule<T>() = p; };
auto nullProcess  = as<AstNullProcess>(x3::omit['0']);
auto const choiceActual = as<AstChoiceProcess> (nullProcess > '+' > nullProcess);
auto const choice = rule<AstAnyProcess> ("choice")
     = nullProcess >> !x3::lit('+')
     | choiceActual;
auto const entry = x3::skip(ascii::space) [choice];

} //End namespace
namespace x3 = boost::spirit::x3;
int main() {
    std::string str("0 + ");
    wccs_parser::AstAnyProcess root;
    auto iter = str.begin();
    auto end = str.end();
    bool r = false;
    try {
        r = parse(iter, end, wccs_parser::entry, root);
    } catch (x3::expectation_failure<char const*> const& x) {
        std::cout << "Never runs," << std::endl;
    } catch (x3::expectation_failure<std::string::const_iterator> const& e) {
        std::cout << "me neither" << std::endl;
    }
    if (r) {
        std::cout << str << std::endl << std::endl << " Parses OK: " << std::endl;
        std::cout << "n-------------------------n";
    } else {
        std::cout << "Parsing failedn";
        std::cout << "-------------------------n";
    }
    if (iter != end) std::cout << "Partial match" << std::endl;
    return 0;
}

Answer 1

如果你通过 const_iterator 捕获，你将需要确保const_iterator是你传递解析的内容：

std::string const str("0 + ");

在科里鲁现场观看

#include <boost/config/warning_disable.hpp>
#include <boost/spirit/home/x3.hpp>
#include <boost/spirit/home/x3/support/ast/variant.hpp>
#include <boost/spirit/include/qi_char_class.hpp>
#include <boost/fusion/include/adapt_struct.hpp>
#include <iostream>
#include <string>
#include <vector>
namespace wccs_parser {
    using boost::spirit::x3::variant;
    using boost::spirit::x3::forward_ast;
    struct AstNullProcess;
    struct AstChoiceProcess;
    using AstAnyProcess = variant<
        forward_ast<AstNullProcess>,
        forward_ast<AstChoiceProcess>
    >;
    struct AstNullProcess {};
    struct AstChoiceProcess {
        AstAnyProcess left;
        AstAnyProcess right;
    };
} // End namespace
BOOST_FUSION_ADAPT_STRUCT(wccs_parser::AstChoiceProcess, left, right)
namespace wccs_parser {
    namespace x3 = boost::spirit::x3;
    using x3::expectation_failure;
    template <typename T> auto rule = [](const char* name = typeid(T).name()) {
         struct _{};
         return x3::rule<_, T> {name};
    };
    template <typename T> auto as = [](auto p, const char* name = typeid(T).name()) { return rule<T>(name) = p; };
    auto nullProcess  = as<AstNullProcess>(x3::omit['0'], "nullProcess");
    auto const choiceActual = as<AstChoiceProcess> (nullProcess > '+' > nullProcess, "choiceActual");
    auto const choice = rule<AstAnyProcess> ("choice")
         = nullProcess >> !x3::lit('+')
         | choiceActual;
    auto const entry = x3::skip(x3::ascii::space) [choice];
}
int main() {
    std::string const str("0 + ");
    try {
        auto iter = str.cbegin();
        auto end = str.cend();
        wccs_parser::AstAnyProcess root;
        bool const r = parse(iter, end, wccs_parser::entry, root);
        if (r) {
            std::cout << str << "nn Parses OK: n";
            std::cout << "n-------------------------n";
        } else {
            std::cout << "Parsing failedn";
            std::cout << "-------------------------n";
        }
        if (iter != end) {
            std::cout << "Partial match, leaving '" << std::string(iter,end) << "'n";
        }
    } catch (wccs_parser::expectation_failure<std::string::const_iterator> const& e) {
        std::cout << "Expected: " << e.which() << " at '" << std::string(e.where(), str.end()) << "'n";
        return 1;
    }
}

指纹

Expected: nullProcess at ' '