提升灵气因记忆违规而崩溃

但我不明白为什么......？

http://coliru.stacked-crooked.com/a/2912593bb421a35e http://coliru.stacked-crooked.com/a/2912593bb421a35e

#include <boost/fusion/adapted/struct.hpp>
#include <boost/spirit/include/qi.hpp>

namespace bsq = boost::spirit::qi;

int main()
{        
    std::uint16_t major, minor, build, revision;

    auto versionParser =
        bsq::uint_
        >> -('.' >> bsq::uint_)
        >> -('.' >> bsq::uint_)
        >> -('.' >> bsq::uint_);

    std::string version = "3.5.1";

    auto start = version.begin();
    if (!bsq::parse(start, version.end(), versionParser, major, minor, build, revision))
    {
        std::cout << "Error!\n";
    }

    std::cout << major << "-" << minor << "-" << build << "-" << revision << std::endl;

    return 0;
}

致电给parse()导致内存访问冲突。

我发誓我曾经有过这个工作，但是……也许我在做白日梦。我已经在 Windows 上使用 Visual Studio 2017 进行了尝试，也在 Coliru 上使用 clang 进行了尝试。我看不到错误。

谢谢。

问题是使用auto表达式来捕获规则，从解析器表达式推导出类型。该类型是一个原始表达式树，它通过引用捕获任何关系，但这意味着许多中间体在封闭的结束后就消失了充分表达 http://eel.is/c++draft/intro.execution#def:full-expression (see C++：临时参数的寿命？ https://stackoverflow.com/questions/2506793/c-life-span-of-temporary-arguments).

这是众所周知的，正如您在这里看到的：

• 将解析器分配给自动变量 https://stackoverflow.com/questions/22023779/assigning-parsers-to-auto-variables/22027181#22027181
• boost Spirit V2 qi 与优化级别相关的错误 https://stackoverflow.com/questions/20763665/boost-spirit-v2-qi-bug-associated-with-optimization-level/20766909#20766909
• boost::spirit::qi::phrase_parse 中某处未定义的行为 https://stackoverflow.com/questions/26410498/undefined-behaviour-somewhere-in-boostspiritqiphrase-parse
• 还有更多

这是最简单的修复：

auto versionParser = bsq::copy(
    bsq::uint_
    >> -('.' >> bsq::uint_)
    >> -('.' >> bsq::uint_)
    >> -('.' >> bsq::uint_));

If you also fix缺少局部变量的初始化它可以正常工作：

Live On Coliru http://coliru.stacked-crooked.com/a/fd704b7026c7fb3e

#include <boost/fusion/adapted/struct.hpp>
#include <boost/spirit/include/qi.hpp>

namespace bsq = boost::spirit::qi;

int main()
{    
    std::cout << "BOOST_VERSION: " << BOOST_VERSION << std::endl;

    std::uint16_t major = 0, minor = 0, build = 0, revision = 0;

    auto versionParser = bsq::copy(
        bsq::uint_
        >> -('.' >> bsq::uint_)
        >> -('.' >> bsq::uint_)
        >> -('.' >> bsq::uint_));

    std::string version = "3.5.1";

    auto start = version.begin();
    if (!bsq::parse(start, version.end(), versionParser, major, minor, build, revision))
    {
        std::cout << "Error!\n";
    }

    std::cout << major << "-" << minor << "-" << build << "-" << revision << std::endl;
}

Prints

BOOST_VERSION: 106600
3-5-1-0

补充笔记

1. 为了避免整个“统一属性”的情况，让解析器分配给所有元素，即使在输入文本中未指定：

       >> ('.' >> bsq::uint_ | bsq::attr(0))
       >> ('.' >> bsq::uint_ | bsq::attr(0))
       >> ('.' >> bsq::uint_ | bsq::attr(0))
   

2. 诊断存在尾随“垃圾”的错误（例如"3.4bogus"），您可以添加一个检查来检查完整的输入是否被解析：

   auto versionParser = bsq::copy(
       bsq::uint_
       >> ('.' >> bsq::uint_ | bsq::attr(0))
       >> ('.' >> bsq::uint_ | bsq::attr(0))
       >> ('.' >> bsq::uint_ | bsq::attr(0))
       >> bsq::eoi);
   

3. 因为版本在语义上是一个元组，为什么不这样表示它呢？

   using Version = std::tuple<uint16_t, uint16_t, uint16_t, uint16_t>;
   Version parsed;
   
   if (!bsq::parse(version.begin(), version.end(), versionParser, parsed))
       std::cout << "Error!\n";
   

   这样你甚至可以说：

   using boost::fusion::operator<<;
   
   auto obsolete = parsed < Version(3, 4, 0, 0);
   std::cout << "Version " << parsed << " " << (obsolete? "too old" : "supported") << "\n";
   

结合这些：

Live On Coliru http://coliru.stacked-crooked.com/a/64b16260c559556e

#include <boost/fusion/adapted/std_tuple.hpp>
#include <boost/spirit/include/qi.hpp>

namespace bsq = boost::spirit::qi;

int main() {    
    auto versionParser = bsq::copy(
        bsq::uint_
        >> ('.' >> bsq::uint_ | bsq::attr(0))
        >> ('.' >> bsq::uint_ | bsq::attr(0))
        >> ('.' >> bsq::uint_ | bsq::attr(0))
        >> bsq::eoi);

    std::string version = "3.5.1";

    using Version = std::tuple<uint16_t, uint16_t, uint16_t, uint16_t>;
    Version parsed;

    if (!bsq::parse(version.begin(), version.end(), versionParser, parsed))
        std::cout << "Error!\n";

    using boost::fusion::operator<<;

    auto obsolete = parsed < Version(3, 4, 0, 0);
    std::cout << "Version " << parsed << " " << (obsolete? "too old" : "supported") << "\n";
}

Prints

Version (3 5 1 0) supported

std::tuple sucks?

我同意。因此，等效地编写您自己的结构：

Live On Coliru http://coliru.stacked-crooked.com/a/86b37d7460bd6db1

struct Version {
    uint16_t major, minor, revision, build;

    auto key() const { return std::tie(major, minor, revision, build); }
    bool operator<(Version const& b) const { return key() < b.key(); }
};

BOOST_FUSION_ADAPT_STRUCT(Version, major, minor, revision, build)

与时俱进

请注意，Spirit X3（进入振奋精神；齐还是X3？ https://stackoverflow.com/questions/52990661/getting-into-boost-spirit-qi-or-x3/52991170#52991170) 没有auto-您遇到的问题：

Live On Coliru http://coliru.stacked-crooked.com/a/93a33781789224ea

#include <boost/fusion/adapted/struct.hpp>
#include <boost/spirit/home/x3.hpp>

#include <boost/fusion/include/io.hpp>
#include <iostream>

namespace bsx = boost::spirit::x3;

struct Version {
    uint16_t major, minor, revision, build;

    auto key() const { return std::tie(major, minor, revision, build); }
    bool operator<(Version const& b) const { return key() < b.key(); }
};

BOOST_FUSION_ADAPT_STRUCT(Version, major, minor, revision, build)

int main() {    
    auto versionParser = bsx::uint_
        >> ('.' >> bsx::uint_ | bsx::attr(0))
        >> ('.' >> bsx::uint_ | bsx::attr(0))
        >> ('.' >> bsx::uint_ | bsx::attr(0))
        >> bsx::eoi;

    std::string version = "3.5.1";

    Version parsed;

    if (!parse(version.begin(), version.end(), versionParser, parsed))
        std::cout << "Error!\n";

    using boost::fusion::operator<<;

    auto obsolete = parsed < Version{3, 4, 0, 0};
    std::cout << "Version " << parsed << " " << (obsolete? "too old" : "supported") << "\n";
}

打印也一样。