Bug在std :: regex？ [英] Bug in std::regex?

问题描述

以下是代码：

#include <string>
#include <regex>
#include <iostream>

int main()
{
    std::string pattern("[^c]ei");
    pattern = "[[:alpha:]]*" + pattern + "[[:alpha:]]*";
    std::regex r(pattern); 
    std::smatch results;   
    std::string test_str = "cei";

    if (std::regex_search(test_str, results, r)) 
        std::cout << results.str() << std::endl;      

    return 0;
}

输出：

cei

使用的编译器是 gcc 4.9.1 。

我是一个新手学习正则表达式。我期望什么都不应该输出，因为 cei与此处的模式不匹配。我做的对吗？有什么问题？

I'm a newbie learning regular expression.I expected nothing should be output,since "cei" doesn't match the pattern here. Am I doing it right? What's the problem?

更新：

此报告已被报告并确认为错误，详情请访问：
https://gcc.gnu.org /bugzilla/show_bug.cgi?id=63497

This one has been reported and confirmed as a bug, for detail please visit here : https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63497

推荐答案

这是实施中的错误。不仅仅是一对夫妇其他工具我尝试同意你的模式不匹配你的输入，但我尝试这：

It's a bug in the implementation. Not only do a couple other tools I tried agree that your pattern does not match your input, but I tried this:

#include <string>
#include <regex>
#include <iostream>

int main()
{
  std::string pattern("([a-z]*)([a-z])(e)(i)([a-z]*)");
  std::regex r(pattern);
  std::smatch results;
  std::string test_str = "cei";

  if (std::regex_search(test_str, results, r))
  {
    std::cout << results.str() << std::endl;

    for (size_t i = 0; i < results.size(); ++i) {
      std::ssub_match sub_match = results[i];
      std::string sub_match_str = sub_match.str();
      std::cout << i << ": " << sub_match_str << '\n';
    }
  }
}

为了简单起见，我用 [az] 替换了 [：alpha：] code> [^ c] 与 [az] ，因为这似乎使它正常工作。下面是它打印的（Linux x86-64上的GCC 4.9.0）：

This is basically similar to what you had, but I replaced [:alpha:] with [a-z] for simplicity, and I also temporarily replaced [^c] with [a-z] because that seems to make it work correctly. Here's what it prints (GCC 4.9.0 on Linux x86-64):

cei
0: cei
1:
2: c
3: e
4: i
5:

如果我将 [az] 替换为 [^ c] 只是将 f 放在那里，它正确地说，模式不匹配。但是如果我像你这样使用 [^ c] ：

If I replace [a-z] where you had [^c] and just put f there instead, it correctly says the pattern doesn't match. But if I use [^c] like you did:

std::string pattern("([a-z]*)([^c])(e)(i)([a-z]*)");

然后我得到这个输出：

cei
0: cei
1: cei
terminate called after throwing an instance of 'std::length_error'
  what():  basic_string::_S_create
Aborted (core dumped)

因此声称匹配成功， [0]是预期的cei。然后，结果[1]也是cei，我想可能是好的。但结果[2]崩溃，因为它尝试构造一个 std :: string 的长度 18446744073709551614 with begin = nullptr。这个巨型数字是 2 ^ 64 - 2 ，aka std :: string :: npos - 1 我的系统）。

So it claims to match successfully, and results[0] is "cei" which is expected. Then, results[1] is "cei" also, which I guess might be OK. But then results[2] crashes, because it tries to construct a std::string of length 18446744073709551614 with begin=nullptr. And that giant number is exactly 2^64 - 2, aka std::string::npos - 1 (on my system).

所以我认为在某个地方有一个错误的错误，影响可以远远超过一个杂乱的正则表达式匹配 - 它可以在运行时崩溃。

So I think there is an off-by-one error somewhere, and the impact can be much more than just a spurious regex match--it can crash at runtime.

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