Confused about while check

Question

I'm confused about this code:

#include "stdafx.h"
#include "std_lib_facilities.h"

int main()
{
    string name_one;
    string name_two;
    string name_three;    

    cout << "Please enter a name: ";
    cin >> name_one;
    cout << "\nReading data...";

    while (name_one.empty())
    {
        cout << "\nFailed!";
        cout << "Please enter a name: ";
        cin >> name_one;
        cout << "\nReading data...";
    }

    cout << "Completed!\n";

    keep_window_open();
    return 0;
}

It is very easy, but when I debug it and for example I don't write anything but just press Enter, it doesn't do anything. Just keeps showing me a flashing underscore under the line, and if I keep pressing Enter it just jumps line by line. Why does the program not read the condition? What I want is that if the user doesn't write anything, the condition in the while starts!

Answer 1

You're using a stream extractor, >>, which is a formatted input function. For many types (such as fundamental types and std::string), these start by skipping all whitespace currently in the stream⁽¹⁾, then extracting characters as long as these are a valid representation of the data type you want to extract.

In other words, when you just press Enter on standard input, there will only be a newline character in the stream. A newline is whitespace, so the >> function is still stuck inside its "skip starting whitespace" mode. Only when you enter a non-whitespace character will the second part ("extract characters and try to interpret them as a representation of the extracted type") kick in.

If you want to always read by lines, you can use the getline stream function, or the std::getline function. You can also combine these with an istringstream object for parsing the line.

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⁽¹⁾ This behaviour can be controlled by the stream manipulators skipws and noskipws, or directly by the stream's formatting flags.