提振精神的语法不一致的行为

问题描述

限时删除！！

我有我想要使用一个工作项目有点语法。最低可执行的例子是：

I have a little grammar that I want to use for a work project. A minimum executable example is:

#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wunused-local-typedefs"
#pragma GCC diagnostic ignored "-Wmaybe-uninitialized"
#pragma GCC diagnostic ignored "-Wunused-variable"
#include <boost/spirit/include/karma.hpp>
#include <boost/spirit/include/qi_grammar.hpp>
#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/support_istream_iterator.hpp>
#pragma GCC diagnostic pop // pops

#include <iostream>

int main()

{
    typedef  unsigned long long ull;

    std::string curline = "1;2;;3,4;5";
    std::cout << "parsing:  " << curline << "\n";

    namespace qi = boost::spirit::qi;
    auto ids = -qi::ulong_long % ','; // '-' allows for empty vecs.
    auto match_type_res = ids % ';' ;
    std::vector<std::vector<ull> > r;
    qi::parse(curline.begin(), curline.end(), match_type_res, r);

    std::cout << "got:      ";
    for (auto v: r){
        for (auto i : v)
            std::cout << i << ",";
        std::cout << ";";
    }
    std::cout <<"\n";
}

在我个人的机器这将产生正确的输出：
解析：1; 2 ;; 3,4; 5
有：1，2，3,4 ;;; 5，;

On my personal machine this produces the correct output:parsing: 1;2;;3,4;5got: 1,;2,;;3,4,;5,;

但在工作中它产生：
解析：1; 2 ;; 3,4; 5
有：1，; 2，; 3，

But at work it produces:parsing: 1;2;;3,4;5got: 1,;2,;;3,

在换句话说，它未能尽快有一个以上的元素的解析长整数的向量在它

In other words, it fails to parse the vector of long integers as soon as there's more than one element in it.

现在，我已经确定了工作的系统使用的是提升1.56，而我的私人计算机使用的是1.57。这是什么原因？

Now, I have identified that the work system is using boost 1.56, while my private computer is using 1.57. Is this the cause?

Knowning我们有一些真正的精神的专家在这里堆栈溢出，我希望有人会知道这个问题是从哪里来的，或者至少可以缩小东西我需要检查的次数。

Knowning we have some real spirit experts here on stack overflow, I was hoping someone might know where this issue is coming from, or can at least narrow down the number of things I need to check.

如果增压版本的问题，我也许可以说服公司进行升级，而是一个解决方法是在任何情况下的欢迎。

If the boost version is the problem, I can probably convince the company to upgrade, but a workaround would be welcome in any case.

推荐答案

您是在调用包含临时的成为的在的含全EX pression结束的¹

Specifically where you use auto to store a parser expression. The Expression Template contains references to temporaries that become dangling at the end of the containing full-expression¹.

UB意味着，任何事情都有可能发生。这两种编译器是正确的！而最好的部分是，根据所使用的编译器标志，你可能会看到不同的行为。

UB implies that anything can happen. Both compilers are right! And the best part is, you will probably see varying behaviour depending on the compiler flags used.

通过对其进行修复或者：

Fix it either by using:

• 齐::复制（或的boost ::原:: DEEP_COPY v.1.55 IIRC之前）


• 使用 BOOST_SPIRIT_AUTO 而不是 BOOST_AUTO （主要是当且仅当您有帮助还支持C ++ 03）



• 使用齐::规则＆LT;＆GT; 和齐::语法＆LT;＆GT; （中非终端）键入擦除和前pressions。这有性能的影响太多，但也提供了更多的功能，如

• qi::copy (or boost::proto::deep_copy before v.1.55 IIRC)
• use BOOST_SPIRIT_AUTO instead of BOOST_AUTO (mostly helpful iff you also support C++03)

• use qi::rule<> and qi::grammar<> (the non-terminals) to type-erase and the expressions. This has performance impact too, but also gives more features like

• 递归规则


• 当地人和继承的属性


• 宣布船长（方便，因为规则可以隐语义[] （见here)


• 更好code组织。

的还要注意的是精神X3承诺砸自动使用有限制。这基本上是一个一大堆更加轻便由于使用C ++ 14的特性。请记住，这还不稳定。的

• 显示与-O2是GCC显示不确定的结果;

• Showing that GCC with -O2 shows undefined results; Live On Coliru

  固定的版本：

  //#pragma GCC diagnostic push
  //#pragma GCC diagnostic ignored "-Wunused-local-typedefs"
  //#pragma GCC diagnostic ignored "-Wmaybe-uninitialized"
  //#pragma GCC diagnostic ignored "-Wunused-variable"
  #include <boost/spirit/include/karma.hpp>
  #include <boost/spirit/include/qi.hpp>
  //#pragma GCC diagnostic pop // pops
  
  #include <iostream>
  
  int main() {
      typedef  unsigned long long ull;
  
      std::string const curline = "1;2;;3,4;5";
      std::cout << "parsing: '" << curline << "'\n";
  
      namespace qi = boost::spirit::qi;
  
  #if 0 // THIS IS UNDEFINED BEHAVIOUR:
      auto ids     = -qi::ulong_long % ','; // '-' allows for empty vecs.
      auto grammar = ids % ';';
  #else // THIS IS CORRECT:
      auto ids     = qi::copy(-qi::ulong_long % ','); // '-' allows for empty vecs.
      auto grammar = qi::copy(ids % ';');
  #endif
  
      std::vector<std::vector<ull> > r;
      qi::parse(curline.begin(), curline.end(), grammar, r);
  
      std::cout << "got:      ";
      for (auto v: r){
          for (auto i : v)
              std::cout << i << ",";
          std::cout << ";";
      }
      std::cout <<"\n";
  }
  

  打印（也与GCC -O2！）：

  Printing (also with GCC -O2!):

  parsing: '1;2;;3,4;5'
  got:      1,;2,;;3,4,;5,;
  

  ---

  ¹（这是基本上是下一个分号在这里;但在standardese）

  ---

  ¹ (that's basically "at the next semicolon" here; but in standardese)

  这篇关于提振精神的语法不一致的行为的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！

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