strange scoping in cpp

Question

My cpp program is doing something strange with scoping when I use it string streams. When I place initialization of the strings and string streams in the same block as where I use it, there are no problems. But if I place it one block above, the string stream doesnt output strings properly

correct behaviour, the program prints each token separated by whitespace:

#include <iostream>
#include <sstream>
#include <string>
using namespace std;

int main () {

    while (true){
        //SAME BLOCK
        stringstream line;
        string commentOrLine;
        string almostToken;
        getline(cin,commentOrLine);
        if (!cin.good()) {
            break;
        }
        line << commentOrLine;
        do{

            line >> almostToken;
            cout << almostToken << " ";
        } while (line);
        cout << endl;
    }
    return 0;
}

Incorrect behavior, the program prints only the first inputline:

#include <iostream>
#include <sstream>
#include <string>
using namespace std;

int main () {
    //DIFFERENT BLOCK
    stringstream line;
    string commentOrLine;
    string almostToken;
    while (true){
        getline(cin,commentOrLine);
        if (!cin.good()) {
            break;
        }
        line << commentOrLine;
        do{

            line >> almostToken;
            cout << almostToken << " ";
        } while (line);
        cout << endl;
    }
    return 0;
}

Why does this happen?

Answer 1

When you "create and destroy" the stringstream for each line, it also gets the fail state reset.

You could fix that by adding line.clear(); just before you add the new content to line.