how to input a vector when size is unknown

1#include <string>
2#include <vector>
3#include <sstream>
4#include <string>
5
6int main()
7{
8    std::vector<int> vec;
9    std::string buffer;
10    int data;
11    std::getline(std::cin, buffer);
12    std::istringstream iss(buffer);
13    while (iss >> data)
14          vec.push_back(data);
15    //foo(vec);   
16}