ifstream如何知道定界符在哪里?

所以当我读取file("animal。txt")时它显示的是

zebra
baboon
orangutan
gorilla
aardvark
lion
tiger
cougar
ocelot
panther
rat
mouse
gerbil
hamster
elephant
rhinoceros
hippopotamus

我想知道ist >> s如何识别分隔符并将长字符串分隔成单独的单词。我在下面提供了一个文本和我的实现。

animal.txt

zebrababoonorangutangorillaaardvarkliontigercougarocelotpantherratmousegerbilhamsterelephantrhinoceroshippopotamus

和

SortedList readFile(string infile)
{
      SortedList result;
      string s;
      ifstream ist(infile.c_str()); // open file
      // Check if file opened correctly
      if(ist.fail()) throw runtime_error("file not found");
      // Read file into list
      while(ist >> s){
          cout<< s << endl;
          cout << ist << endl;
            result.insert(s);
      }
      return result;
}