使用operator >>两次后为什么std :: getline失败？

Question

I have the given input:

 local
 127.0.0.1 localhost
 other
 next

Using the following code the output is a blank where I expected other . The output is "output: "

#include <iostream>
using namespace std;

int main() {
    std::string ip, domain, header;
    std::getline(cin, header);
    cin >> ip >> domain;
    std::getline(cin, header);
    std::cout << "output: " << header;
}

However, I notice this problem occurs when extracting twice ( cin >> ip >> domain; ) before calling std::getline . The code works as I would expect if I had cin >> ip . Why am I seeing this weird result when I use double extraction( operator>> ) with std::getline ?

Answer 1

Stream operator>> extracts whitespace which is before the data it extracts, not after. This means it extracts "localhost" into domain , but leaves following the newline in the stream. getline() then reads just this newline.