getline() does not work if used after some inputs [duplicate]

Question

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Need help with getline()

getline() is not working, if I use it after some inputs, i.e.

#include<iostream>
using namespace std;

main()
{
string date,time;
char journal[23];


cout<<"Date:\t";
cin>>date;
cout<<"Time:\t";
cin>>time;

cout<<"Journal Entry:\t";
cin.getline(journal,23);


cout<<endl;
system("pause");
}

where as if I use getline() on top of inputs, it does work i.e.

cout<<"Journal Entry:\t";
cin.getline(journal,23);
cout<<"Date:\t";
cin>>date;
cout<<"Time:\t";
cin>>time;

What might be the reason?

Makhachkala

Please define "is not working". What results did you expect, and what did you get? – Unclassical

Answer 1

Characters are extracted until either (n - 1) characters have been extracted or the delimiting character is found (which is delimiter if this parameter is specified, or '\n' otherwise). The extraction also stops if the end of the file is reached in the input sequence or if an error occurs during the input operation.

When cin.getline() reads from the input, there is a newline character left in the input stream, so it doesn't read your c-string. Use cin.ignore() before calling getline().

cout<<"Journal Entry:\t";
cin.ignore();
cin.getline(journal,23);

Repugn

what's about int still \n caused the problem for getline()? – Harappa

This is so important thing and is not mentioned in many of the websites explaining the functionality of getline. – Cohlette

Answer 2

Adding to what @DavidHammen said:

The extraction operations leave the trailing '\n' character in the stream. On the other hand, istream::getline() discards it. So when you call getline after an extraction operator, '\n' is the first character it encounters and it stops reading right there.

Put this after before getline call extraction:

cin.ignore()

A more robust way of taking input would be something like this:

while (true) {

    cout<<"Time:\t";
    if (cin>>time) {
        cin.ignore();  // discard the trailing '\n'
        break;
    } else {
        // ignore everything or to the first '\n', whichever comes first
        cin.ignore(numeric_limits<streamsize>::max(), '\n');
        cin.clear();  // clear the error flags
        cout << "Invalid input, try again.\n";
    }
}

Econometrics

Answer 3

You're not checking stream status. The std::cin stream extraction operator (operator>>) can fail. When it does, the stream is marked as "bad" (failbit, badbit, or eofbit are set). Once "bad", all subsequent stream extractions on that stream will fail unless you clear the status.

Learn to be a paranoid programmer. Always check status of those formatted input operations. You could, for example throw an exception, or print an error message and exit. The one thing you shouldn't do is to simply assume that it worked.

Beckybecloud