sstream string wrong output - c++

Question

I am trying to read a string of three number using sstream but when I try to print them, I am getting a wrong output with four numbers.
Code:
#include <iostream>
#include <sstream>
using namespace std;
int main() {
string a("1 2 3");
istringstream my_stream(a);
int n;
while(my_stream) {
my_stream >> n;
cout << n << "\n";
}
}
Output:
1
2
3
3
Why I get four numbers in the output compared to three numbers in input string?

Answer 1

Here
while ( my_stream )
my_stream is convertible to bool and returns true if there's no I/O error.
See: https://en.cppreference.com/w/cpp/io/basic_ios/operator_bool
So, after the last reading, there's no I/O error yet, so it iterates again and there's an error and nothing is read into n in this statement:
my_stream >> n;
And, std::cout prints the last extracted value again i.e. 3.
The solution could be to directly check I/O error after reading in while (preferred):
while ( my_stream >> n )
{
std::cout << n << '\n';
}
or, print only if the reading is successful using an if:
while ( my_stream )
{
if ( my_stream >> n ) // print if there's no I/O error
{
std::cout << n << '\n';
}
}
Example (live):
#include <iostream>
#include <sstream>
int main()
{
std::string a { "1 2 3" };
std::istringstream iss{ a };
int n {0};
while ( iss >> n )
{
std::cout << n << '\n';
}
return 0;
}
Output:
1
2
3
Relevant: Why is "using namespace std;" considered bad practice?

Answer 2

You are printing the data before checking if readings are successful.
while(my_stream) {
my_stream >> n;
should be
while(my_stream >> n) {
Related (doesn't seem duplicate because eof() isn't used here):
c++ - Why is iostream::eof inside a loop condition (i.e. while (!stream.eof())) considered wrong? - Stack Overflow