c++ - 正则表达式可以，但不起作用

Question

这段代码不起作用，为什么？

std::cmatch result;
std::string str("trucmuch.service\n   Loaded: not-found (Reason: No such file or directory)\n   Active: inactive (dead)... (101)");
std::regex rgx("Loaded:\s+(\S+)(?:\s+\((?:Reason:\s*)?([^)]*)\))?", std::regex::ECMAScript);
std::regex_match(str.c_str(), result, rgx);
qDebug() << result.size();

显示 0 !!

如何获得结果[0] 和结果 1 ("not-found", "No such file or directory")?

测试regex101

Answer 1

使用 std::regex_search 查找与您的模式匹配的子字符串。您还需要正确地转义反斜杠，或者更好的是，使用原始字符串文字。以下作品:

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

int main()
{
    std::smatch result;

    std::string str =
        "trucmuch.service\n   Loaded: not-found (Reason: No such file "
        "or directory)\n   Active: inactive (dead)... (101)";

    std::regex rgx(R"(Loaded:\s+(\S+)(?:\s+\((?:Reason:\s*)?([^)]*)\))?)",
                   std::regex::ECMAScript);

    std::regex_search(str, result, rgx);

    for (const auto & sm : result) { std::cout << sm << '\n'; }
}