什么std :: match_results :: size返回？ [英] What does std::match_results::size return?

问题描述

我对以下C ++ 11代码感到困惑：

I'm a bit confused about the following C++11 code:

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

int main()
{
    std::string haystack("abcdefabcghiabc");
    std::regex needle("abc");
    std::smatch matches;
    std::regex_search(haystack, matches, needle);
    std::cout << matches.size() << std::endl;
}

我希望它打印出来 3 ，但是我得到 1 。

推荐答案

您会得到 1 ，因为 regex_search 仅返回1个匹配项， code> size（）将返回捕获组的数量和整个匹配值。

You get 1 because regex_search returns only 1 match, and size() will return the number of capture groups + the whole match value.

匹配是...：

Your matches is...:

match_results type（例如cmatch或smatch），其中包含匹配结果和找到的任何子匹配的信息。

Object of a match_results type (such as cmatch or smatch) that is filled by this function with information about the match results and any submatches found.

如果[正则表达式搜索]成功，它不为空，并且包含一系列sub_match对象：第一个 sub_match 元素对应于整个匹配，如果正则表达式包含要匹配的子表达式（即，括号 - 分隔的组），则其对应的子匹配作为连续的子匹配元素存储在match_results中对象。

If [the regex search is] successful, it is not empty and contains a series of sub_match objects: the first sub_match element corresponds to the entire match, and, if the regex expression contained sub-expressions to be matched (i.e., parentheses-delimited groups), their corresponding sub-matches are stored as successive sub_match elements in the match_results object.

这里是一个可以找到多个匹配的代码：

Here is a code that will find multiple matches:

#include <string>
#include <iostream>
#include <regex>
using namespace std;
int main() {
  string str("abcdefabcghiabc");
  int i = 0;
  regex rgx1("abc");
  smatch smtch;
  while (regex_search(str, smtch, rgx1)) {
        std::cout << i << ": " << smtch[0] << std::endl;
        i += 1;
        str = smtch.suffix().str();
  }
  return 0;
}

查看 IDEONE演示返回 abc 3次。

输入字符串，这里是基于 std :: sregex_iterator （ std :: wsregex_iterator subject是 std :: wstring 对象）：

As this method destroys the input string, here is another alternative based on the std::sregex_iterator (std::wsregex_iterator should be used when your subject is an std::wstring object):

int main() {
    std::regex r("ab(c)");
    std::string s = "abcdefabcghiabc";
    for(std::sregex_iterator i = std::sregex_iterator(s.begin(), s.end(), r);
                             i != std::sregex_iterator();
                             ++i)
    {
        std::smatch m = *i;
        std::cout << "Match value: " << m.str() << " at Position " << m.position() << '\n';
        std::cout << "    Capture: " << m[1].str() << " at Position " << m.position(1) << '\n';
    }
    return 0;
}

请参阅 IDEONE演示，返回

Match value: abc at Position 0
    Capture: c at Position 2
Match value: abc at Position 6
    Capture: c at Position 8
Match value: abc at Position 12
    Capture: c at Position 14

这篇关于什么std :: match_results :: size返回？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IT屋！