Boost Spirit Qi 因内存违规而崩溃答案

【问题标题】：Boost Spirit Qi crashes for memory violationBoost Spirit Qi 因内存违规而崩溃
【发布时间】：2018-10-28 16:10:26
【问题描述】：

但我不知道为什么...？

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;
}

对parse() 的调用会导致内存访问冲突。

我发誓我曾经做过这项工作，但是……也许我是在做白日梦。我已经在 Windows 上使用 Visual Studio 2017 以及在 Coliru 上使用 clang 进行了尝试。我看不到错误。

谢谢。

【问题讨论】：

标签： c++ boost-spirit-qi

【解决方案1】：

问题是使用auto 表达式来捕获规则，它从解析器表达式中推断出类型。该类型是一个原型表达式树，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full-expresion 结束后消失了（参见C++: Life span of temporary arguments?）。

这是众所周知的，你可以在这里看到：

这是最简单的解决方法：

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

如果您还修复了局部变量缺失的初始化，它可以正常工作：

Live On Coliru

#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;
}

打印

BOOST_VERSION: 106600
3-5-1-0

附加说明

为了避免整个“属性统一”的情况，让我们让它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))
```

要诊断尾随“垃圾”的错误（例如 "3.4bogus"），您可以添加一个检查是否已解析完整输入：

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

因为版本在语义上是一个元组，为什么不这样表示呢？

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

#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";
}

打印

Version (3 5 1 0) supported

`std::tuple` 很烂？

我同意。因此，等效地编写自己的结构：

Live On Coliru

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 (Getting into boost spirit; Qi or X3?) 没有您遇到的 auto 问题：

Live On Coliru

#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";
}

同样打印。

【讨论】：

添加了三个改进注释和两个带有实时示例的章节。
谢谢你，@sehe，当我有精神问题时，我总是可以依靠你。 :)

附加说明

std::tuple 很烂？

与时俱进

`std::tuple` 很烂？