regex C++正则表达式简单使用

/* * 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：