c++ assertion string iterator offset out of reange - c++

Question

I am getting Assertion Failed. It show it after cin. I have checked also the file whose path it shows, but no solution.
"string iterator + offset out of range" is the massage it shows. It happens after I use "cin >> a" at line 65. Can anyone help me? Thanks in advance.
#include <iostream>
#include <string>
#include <sstream>
#include <vector>
using namespace std;
int gcd(int a, int b){
cout << "gcd" << endl;
if (b == 0) return a;
else return gcd(b, a % b);
}
int gcd_n(vector<int>nums){
int g;
size_t n = nums.size();
g = nums.at(0);
cout << "son" << endl;
for (int i = 1; i < n; i++){
g = gcd(nums.at(i), g);
}
return g;
}
long long int multi_vect(vector<int> v){
long long int m = 1;
for (size_t i = 0; i < v.size(); i++)
m *= v.at(i);
return m;
}
int main() {
int a;
vector <vector<int>> all_vects;
cin >> a;
string input, sub;
getline(cin, input);
int n = input.find(' ');
vector<int> vect;
while(true){
int num;
sub = input.substr(0, n);
istringstream(sub) >> num;
vect.push_back(num);
input = input.substr(n+1, input.back()+1);
n = input.find(' ');
if (n == -1){
istringstream(input) >> num;
vect.push_back(num);
break;
}
}
all_vects.push_back(vect);
}

Answer 1

When I tested this code, I found that n=-1 needs to be judged in advance. Suppose that input. Assuming that the string input has no ' ', then n will become -1, And the sub = input.substr(0, n); is not true. So, the vector vect will be empty. That is why string iterator + offset out of range will appear.
The following are my changes to this code. And you could refer to it.
if (n == -1)
{
istringstream(input) >> num;
vect.push_back(num);
break;
}
else {
sub = input.substr(0, n);
istringstream(sub) >> num;
vect.push_back(num);
input = input.substr(n + 1, input.back() + 1);
n = input.find(' ');
}