c++字符串操作

#include <iostream>
#include <string>
using namespace std;
int main()
{
    string nam("http://1212121");
    if (nam.compare(0, 4, "http") == 0)
    {
        cout<<"equal"<<endl;
    }
    cout<<nam.substr(0,4)<<endl;
    string num("0123456789");
    string n("1a3");
    if (num.find(n[0]) != string::npos) {
        cout<<"container"<<endl;
    }
    if (num.find(n[1]) == string::npos) {
        cout<<" no container"<<endl;
    }
    cout<<num.find(n[1])<<endl;

    string ip("http://128.0.0.1/alibab.com");
    if (ip.find("127.0.0.1") == string::npos){
        cout<<" no ip container"<<endl;
    }
    return 0;
}

output:

equal
http
container
no container
18446744073709551615
no ip container