# Extra Clang Tools 21.1.8 documentation

## clang-tidy - bugprone-nondeterministic-pointer-iteration-order

# bugprone-nondeterministic-pointer-iteration-order

Finds nondeterministic usages of pointers in unordered containers.

One canonical example is iteration across a container of pointers.

    {
      int a = 1, b = 2;
      std::unordered_set<int *> UnorderedPtrSet = {&a, &b};
      for (auto i : UnorderedPtrSet)
        f(i);
    }

Another such example is sorting a container of pointers.

    {
      int a = 1, b = 2;
      std::vector<int *> VectorOfPtr = {&a, &b};
      std::sort(VectorOfPtr.begin(), VectorOfPtr.end());
    }

Iteration of a containers of pointers may present the order of different pointers differently across different runs of a program. In some cases this may be acceptable behavior, in others this may be unexpected behavior. This check is advisory for this reason.

This check only detects range-based for loops over unordered sets and maps. It also detects calls sorting-like algorithms on containers holding pointers. Other similar usages will not be found and are false negatives.

Limitations:

- This check currently does not check if a nondeterministic iteration order is likely to be a mistake, and instead marks all such iterations as bugprone.

- std::reference_wrapper is not considered yet.

- Only for loops are considered, other iterators can be included in improvements.