CODEWITHSUNDEEP
c++vector
Raman Sharma
Raman Sharma

Reputation: 281

Unable to print the first element of the string

I am converting a String to an integer and then passing to a vector and then print it but the first element of the string does not get printed.

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

vector<int> parseInts(string str) {
       stringstream ss(str);
       vector<int> my;
       char ch;
       int num;
       while(ss.good()){
           string substr;
           getline(ss, substr, ',');
           ss >> num;
           my.push_back(num);
       }
       return my;
}

int main() {
    string str;
    cin >> str;
    vector<int> integers = parseInts(str);
    for(int i = 0; i < integers.size(); i++) {
        cout << integers[i] << "\n";
    }

    return 0;
}

i am converting a string to integer and then passes to a vector and then print it but the first element of the string is not get printed

Upvotes: 0

Views: 118

Answers (1)

David G
David G

Reputation: 96810

The main issue is the ss >> num line. We first start with 1,2,3,4,5 in the stream. getline(ss, substr, '\n') reads the first number from the stream (1) and gets rid of the delimiter ,. Then ss >> num reads the next number (2) but keeps the next , in the stream because the formatted operator >> only reads as many characters that are valid for the type its being read into. So you threw away the 1 that was stored inside substr and pushed in 2 to the vector.

So the stream at this point is ,3,4,5 by the second iteration of the loop. getline reads an empty string into substr (because there's no number before the ,) and gets rid of the the delimiter , and ss >> num reads 3. This repeats until the entire stream is read: getline constantly reads an empty string and ss >> num reads in the integer.

The solution is to get rid of the ss >> num line and convert substr to an integer with std::stoi. Also, as a matter of correctness you should put the input operation into the condition of the while loop. This way the loop is entered after checking if the input operation succeeded.

std::string substr;
while (getline(ss, substr, ',')) {
  my.push_back(std::stoi(substr));
}

Upvotes: 2

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