CERT C++: CTR51-CPP

Use of invalid iterator occurs when you use an iterator, pointer, or reference to a container element that has been invalidated by actions such as insertion or erasure. For instance, consider this code:

std::vector<int> v = {1,2,3,4,5,6,7};
std::vector<int>::iterator it = std::find(v.begin(), v.end(), 5);
v.push_back(-1);
std::cout<<*it;

Certain erasure operations, such as std::deque::pop_back() or std::forward_list::pop_front() invalidate the iterators to the erased elements. After the erasure, whether any iterators pointed to the erased elements is unknown. If invalidated iterators that point to the erased elements exist in your code, Polyspace does not flag them.

Certain operations return iterators through an std::pair. Polyspace does not track iterators that are part of an std::pair.

Dereferencing the invalid iterator might produce unexpected results. If the invalidated iterator becomes a dangling pointer or an uninitialized pointer, you might not be able to dereference it safely.

The C++ standard defined which operations invalidate the iterators of the standard library containers. See Containers library. When performing actions that might invalidate an iterator, validate the iterator, for instance, by recalculating its position.

#include <deque>


void foo(const int *Value, std::size_t count)
{
  std::deque<int> DQ;
  auto It = DQ.begin();
  for (std::size_t i = 0; i < count; ++i, ++It) {
    DQ.insert(It, Value[i] + 42);//Noncompliant
  }
}

In this example, the first DQ.insert() operation invalidates the iterator It. Its subsequent use might result in undefined behavior. Polyspace flags the use of the invalid operator.

When using iterators after an insertion or erasure, update the iterator to avoid undefined behavior. For instance, in this code, It is updated after each insertion so that the iterator remains valid.

#include <deque>


void foo(const int *Value, std::size_t count)
{
  std::deque<int> DQ;
  auto It = DQ.begin();
  for (std::size_t i = 0; i < count; ++i, ++It) {
    It = DQ.insert(It, Value[i] + 41.0);//Compliant
  }
}