(Unsolved problem) C++ about the problem that the cin stream cannot be restored after while (cin ＞＞ ). Anyone who knows how to restore the cin stream is very grateful! ! !

#include <iostream>
#include <string>
using namespace std;

int main()
{
string str;
//下面这个循环我用文件结束符结束后，后续调用cin.clear()
while(cin >> str)
        cout << str << " ";
cin.clear();
string str_1;
//虽然前面调用clear,但是下面这个cin还是不能用为什么？哪位告诉我下，不胜感激。
cin >> str_1;
cout << str_1 << endl;

return 0;
}
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