使用cin在while循环中进行条件

Question

I have following code

 //in main
 int x;
 while ( cin>>x ){
        // code goes here
 }

Now,i know that this loop executes untill read to x fails which occurs when type mismatch occurs
So pressing a char lets me to come out of loop as x is of type int and char will not be read from input stream.
But problem is with whitespaces, as they are also not int so why loop does not ends when i press enter or whitespace?

Answer 1

According to The C++ Programming Language Special Edition , $21.9 Advice [5]:

Remember that by default >> skips whitespace; §21.3.2.

And in $21.3.2:

Whitespace is defined as the standard C whitespace (blank, tab, newline, formfeed, and carriage return) by a call to isspace() as defined in (§20.4.2).

Answer 2

The comment of @jrok provided the answer.

Hence, as long as the input is a white space cin waits for input which may represent the requested type. It stops if an invalid character is in the stream or - after a valid non white space character has been consumed - the character is a white space.

You might read line by line to detect empty input:

std::string line
while(getline(cin, line)) {
    // Note: Omitting the case where the line contains spaces, only.
    if(line.empty()) {
       // No input;
       break;
    }
    else {
       // Parse and process the line.
    }
}

Note: If skipping white spaces is disabled, the behavior changes.