Read empty lines C++

Question

I am having trouble reading and differentiating empty lines from an input.

Here's the sample input:

 number

 string
 string
 string
 ...

 number

 string
 string
 ...

Each number represents the start of an input and the blank line after the sequence of strings represents the end of an input. The string can be a phrase, not only one word.

My code does the following:

  int n;

  while(cin >> n) { //number

    string s, blank;
    getline(cin, blank); //reads the blank line

    while (getline(cin, s) && s.length() > 0) { //I've tried !s.empty()
        //do stuff
    }
  }

I've tried directly cin >> blank, but it didn't work.

Can someone help me solve this issue?

Thanks!

Solution

After you read the number with this line:

while(cin >> n) { //number

cin doesn't read anything after the last digit. That means cin's input buffer still contains the rest of the line that the number was on. So, you need to skip that line, and the next blank line. You could do that by just using getline twice. i.e.

while(cin >> n) { //number

    string s, blank;
    getline(cin, blank); // reads the rest of the line that the number was on
    getline(cin, blank); // reads the blank line

    while (getline(cin, s) && !s.empty()) {
        //do stuff
    }
  }

Comments

[Diffy]

Isnt it because getLine() stops at seeing a whitespace character. So 1st getLine() will consume the whitespace character and the 2nd getLine() will consume the blank line. The solution given is anyways correct.

[Mampac]

why then continuous prompting for a number doesn't result in a cin error; only after the last one, an empty string passed to the next cin? for example, if i cin >> n three times in a row, then cin >> string, the string will be empty, but the previous cins didn't trigger a failure