void FCN (const string& The filename, vector & Vec) 
{
Ifstream in (filename); 
If (in) 
{
String buf. 
While (in> Buf) 
{
Vec. Push_back (buf); 
} 
} 
The else 
cout <"Fail to open the file!" } 

Why a "in the while in> Buf "can solve will be in according to the content of a word as a separate element in the vec?