c++c++11iterationunordered-set

How does one iterate through an unordered set in C++?


Suppose I have an unordered set

unordered_set<int> my_set;
myset.insert(1);
myset.insert(2);
myset.insert(3);

How do I iterate through it? I don't need to iterate in any order - just as long as I reach each element once. I tried

for (int i = 0; i < my_set.size(); i++)
     cout << my_set[i];

to no avail.


Solution

  • You can use the new range-based for loop:

    std::unordered_set<T> mySet;
    for (const auto& elem: mySet) {
        /* ... process elem ... */
    }
    

    Or, you can use the more traditional iterator-based loop:

    std::unordered_set<T> mySet;
    for (auto itr = mySet.begin(); itr != mySet.end(); ++itr) {
        /* ... process *itr ... */
    }
    

    Or, if you don't have auto support, perhaps because you don't have C++11 support on your compiler:

    std::unordered_set<T> mySet;
    for (std::unordered_set<T>::iterator itr = mySet.begin(); itr != mySet.end(); ++itr) {
        /* ... process *itr ... */
    }