regex C++正则表达式简单使用

痛定思痛。 2022-06-05 06:58 207阅读 0赞

/*
     * 正则表达式是在运行时而非编译时编译的
     * 构造一个regex或对一个已有的regex赋新值可能非常耗时
     * 我们应该尽量避免不必要的regex
     */
    
    #include <iostream>
    #include <regex>
    #include <string>
    
    using namespace std;
    
    int main2()
    {
        //搜索关键字为ei且前面不是紧接c
        string pattern("[^c]ei");
        pattern = "[[:alpha:]]*"+pattern+"[[:alpha:]]*";
        regex r(pattern);
        //smatch 容器类，保存string中搜索的结果
        smatch result;
        string test_str = "recepit freind theif receive";
    //    if(regex_search(test_str,result,r)){  //regex_search找到一个就停止了
    //        cout<<result.str()<<endl;
    //    }
        int i=0;
        while (std::regex_search (test_str,result,r)) {
            for (auto x:result)
                std::cout << i++ << " :" << x << " "<<std::endl;
            test_str = result.suffix().str();//当前结果的后续字段
            test_str.erase(0,test_str.find_first_not_of(" "));
            cout<<test_str<<endl;
        }
        return 0;
    }
    int main1 ()
    {
        std::string s ("there is a needle in this haystack");
        std::smatch m;
        std::regex e ("needle");
    
        std::cout << "searching for needle in [" << s << "]\n";
        std::regex_search ( s, m, e );
    
        if (m.ready()) {
        std::cout << m[0] << " found!\n";
        std::cout << "prefix: [" << m.prefix() << "]\n";
        std::cout << "suffix: [" << m.suffix() << "]\n";
        }
    
        return 0;
    }
    int main(){
        std::string s ("there is a needle in this haystack");
        //match参数类型与输入序列不匹配，在下面的regex_search使用了一个char*
        std::cmatch m;
        std::regex e ("needle");
    
        std::cout << "searching for needle in [" << s << "]\n";
        std::regex_search ( "there is a needle in this haystack", m, e );
    
        cout<<m[0]<<endl;
    
        return 0;
    }

调整main的结构（去掉main后面的数字把其他的加上数字让它只有一个main有效）调出的结果依次是：

![Center][]

![Center 1][]

![Center 2][]

[Center]: /images/20220605/4c59b2c638d44147b04b327cfb3f3cfb.png
[Center 1]: /images/20220605/8f3bbb7adaca4558b2288a3846c3a550.png
[Center 2]: /images/20220605/40028a71dd0e4286ab1f62175e75b118.png