对于任意std::regex
,是否可以知道其中的捕获组数目?
假设结果将由函数CountCaptures()
返回。这就是我想要得到的:
std::regex r1("(a)bc");
int i = CountCaptures(r1); // returns 1
std::regex r2("(a)(b)c");
int j = CountCaptures(r2); // returns 2
std::regex r3("abc");
int k = CountCaptures(r3); // returns 0
我知道在匹配字符串之后,std::smatch
可以做到这一点,但事实是,我从用户处接收到一个正则表达式,并且需要在匹配任何字符串之前以某种方式限制捕获组。 / p>
答案 0 :(得分:3)
您可以使用std::basic_regex::mark_count()
。
示例用法
std::regex r1{"abcde"};
std::cout << "r1 has " << r1.mark_count() << " capture groups" << '\n';
std::regex r2{"ab(c)de"};
std::cout << "r2 has " << r2.mark_count() << " capture groups" << '\n';
std::regex r3{"abc(de(fg))"};
std::cout << "r3 has " << r3.mark_count() << " capture groups" << '\n';
输出:
r1 has 0 capture groups
r2 has 1 capture groups
r3 has 2 capture groups