c++ - 无限循环与 RE2::FindAndConsumeN

Question

我正在尝试计算某个模式在表达式中出现的次数:

while (RE2::FindAndConsumeN(&stringPiece, regex, nullptr, 0))
{
    ++matches;
}

测试它:

auto stringPiece = RE2::StringPiece("aaa");
auto regexp = RE2::re2("a*");

以永远运行的循环结束(我预计它会返回 1)有谁知道我怎么用错了？

谢谢

Answer 1

TL;DR findAndConsume 的查找失败，因为它无法找到输入开头的内容。失败意味着找到了匹配项，但我猜它无法正确移动缓冲区，从而导致无限循环。

---

根据 header of re2 :

  // Like Consume(..), but does not anchor the match at the beginning of the
  // string.  That is, "pattern" need not start its match at the beginning of
  // "input".  For example, "FindAndConsume(s, "(\\w+)", &word)" finds the next
  // word in "s" and stores it in "word".

That is, "pattern" need not start its match at the beginning of "input"

在您的代码中，您的模式在输入的开头匹配，因此是错误的行为。

如果你给 findAndConsume 提供类似的东西:

auto stringPiece = RE2::StringPiece("baaa");

你的循环中应该没有更多的错误。

或者，如果你愿意，你可以使用 ConsumeN() 代替:

  // Like FullMatch() and PartialMatch(), except that pattern has to
  // match a prefix of "text", and "input" is advanced past the matched
  // text.  Note: "input" is modified iff this routine returns true.
  static bool ConsumeN(StringPiece* input, const RE2& pattern, // 3..16 args
                       const Arg* const args[], int argc);