Difference between std::regex_match amp; std::regex_search?(std::regex_match amp; 之间的区别std::regex_search?)

问题描述

编写了以下程序以使用 C++11 std::regex_match &std::regex_search.但是，使用第一种方法返回 false，第二种方法返回 true(预期).我阅读了文档并且已经存在与此相关的 SO 问题，但是我不明白这两种方法之间的区别以及何时应该使用它们中的任何一种?对于任何常见问题，它们都可以互换使用吗?

Below program has been written to fetch the "Day" information using the C++11 std::regex_match & std::regex_search. However, using the first method returns false and second method returns true(expected). I read the documentation and already existing SO question related to this, but I do not understand the difference between these two methods and when we should use either of them? Can they both be used interchangeably for any common problem?

regex_match 和 regex_search 的区别?

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

int main()
{
    std::string input{ "Mon Nov 25 20:54:36 2013" };
    //Day:: Exactly Two Number surrounded by spaces in both side
    std::regex  r{R"(sd{2}s)"};
    //std::regex  r{"\s\d{2}\s"};
    std::smatch match;

if (std::regex_match(input,match,r)) {
        std::cout << "Found" << "
";
    } else {
        std::cout << "Did Not Found" << "
";
    }

    if (std::regex_search(input, match,r)) {
        std::cout << "Found" << "
";
        if (match.ready()){
            std::string out = match[0];
            std::cout << out << "
";
        }
    }
    else {
        std::cout << "Did Not Found" << "
";
    }
}

输出

Did Not Found

Found

 25 

在这种情况下，为什么第一个正则表达式方法返回 false?.regex 似乎是正确的，所以理想情况下两者都应该返回 true.我通过将 std::regex_match(input,match,r) 更改为 std::regex_match(input,r) 来运行上面的程序，发现它仍然返回 <代码>假.

Why first regex method returns false in this case?. The regex seems to be correct so ideally both should have been returned true. I ran the above program by changing the std::regex_match(input,match,r) to std::regex_match(input,r) and found that it still returns false.

有人能解释一下上面的例子，以及这些方法的一般用例吗?

Could somebody explain the above example and, in general, use cases of these methods?

推荐答案

regex_match 仅在整个输入序列匹配时返回 true，而 regex_search<即使只有一个子序列与 regex 匹配，/code> 也会成功.