c++ - std::getline does not work inside a for-loop

Question

I'm trying to collect user's input in a string variable that accepts whitespaces for a specified amount of time.

Since the usual cin >> str doesn't accept whitespaces, so I'd go with std::getline from <string>

Here is my code:

#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
using namespace std;
int main()
{
    int n;
    cin >> n;
    for(int i = 0; i < n; i++)
    {
        string local;
        getline(cin, local); // This simply does not work. Just skipped without a reason.
        //............................
    }

    //............................
    return 0;
}

Any idea?

Answer 1

You can see why this is failing if you output what you stored in local (which is a poor variable name, by the way :P):

#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
using namespace std;
int main()
{
    int n;
    cin >> n;
    for(int i = 0; i < n; i++)
    {
        string local;
        getline(cin, local);
        std::cout << "> " << local << std::endl;
    }

    //............................
    return 0;
}

You will see it prints a newline after > immediately after inputting your number. It then moves on to inputting the rest.

This is because getline is giving you the empty line left over from inputting your number. (It reads the number, but apparently doesn't remove the , so you're left with a blank line.) You need to get rid of any remaining whitespace first:

#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
using namespace std;
int main()
{
    int n;
    cin >> n;
    cin >> ws; // stream out any whitespace
    for(int i = 0; i < n; i++)
    {
        string local;
        getline(cin, local);
        std::cout << "> " << local << std::endl;
    }

    //............................
    return 0;
}

This the works as expected.

Off topic, perhaps it was only for the snippet at hand, but code tends to be more readable if you don't have using namespace std;. It defeats the purpose of namespaces. I suspect it was only for posting here, though.