How to build a comma delimited list from strings w/o the extra delimiter at the end? [duplicate]

Answer 1

If you like a solution without a if-clause each time the while loops executes.

#include <iostream>
#include <string>
#include <sstream>

using namespace std;

int main() {

    string str;

    getline(cin, str);
    
    string word;
    istringstream ss(str);
    string delimiter = "";
    while(ss >> word) {
        cout << delimiter << word;
        delimiter = ", ";
    };
}

Answer 2

You are not handling the case when operator>> fails to read a word once the end of the istringstream has been reached, thus leaving your word variable empty. You are outputting the word before checking if the read was actually successful. That is why you end up with a blank word at the end of your output. You would need to check for that condition, eg:

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

int main()
{
    string str;
    getline(cin, str);

    istringstream ss(str);

    do {
        string word;
        if (!(ss >> word)) break;
        cout << word << ", ";
    } 
    while (true);
}

Alternatively:

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

int main()
{
    string str;
    getline(cin, str);

    istringstream ss(str);
    string word;

    while (ss >> word)
    {
        cout << word << ", ";
    } 
}

However, either approach would still leave you with a trailing comma at the end of the last word.

You could use a variable to control when the comma is output, eg:

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

int main()
{
    string str;
    getline(cin, str);

    istringstream ss(str);
    string word;
    bool first = true;

    while (ss >> word)
    {
        if (first)
            first = false;
        else
            cout << ", ";

        cout << word;
    } 
}

But, in this situation, it would be cleaner to simply output the first word by itself, and then enter a loop to output the remaining words prefixed by a comma, eg:

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

int main()
{
    string str;
    getline(cin, str);

    istringstream ss(str);
    string word;

    if (ss >> word)
    {
        cout << word;

        while (ss >> word)
        {
            cout << ", " << word;
        }
    } 
}

Answer 3

This should fix it:

#include <iostream>
#include <string>
#include <sstream>

using namespace std;

int main() {

    string str;

    getline(cin, str);
    
    string word;
    istringstream ss(str);
    bool firstIteration = true;
    while(ss >> word) {
        if(!firstIteration) {
            cout  << ", ";
        }
        cout << word;
        firstIteration = false;
    };
}

Check the working demo here please.

---

I am using this idiom (pattern?) in many programming languages, and all kind of tasks where you need to construct delimited output from list like inputs. Let me give the abstract in pseudo code:

empty output
firstIteration = true
foreach item in list
    if firstIteration
        add delimiter to output
    add item to output
    firstIteration = false

In some cases one could even omit the firstIteration indicator variable completely:

empty output
foreach item in list
    if not is_empty(output)
        add delimiter to output
    add item to output