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Reallocation can occur when a member function modifies its container. Modifying member functions include reserve() and resize(), push_back(), pop_back(), erase(), clear(), insert(), and others. In addition, assignment operations and modifying algorithms can also cause reallocation. When a container reallocates its elements, their addresses change. This applies only to contiguous-memory iterators, in particular std::vector}}s, {{deque}}s and {{string}}s. The {{swap() method of {{string}}s also invalidates iterators, std::deque and std::string.

In general iterators on node-based containers such as {{list}}s are std::list are not invalidated via modification of the container, unless the element referenced by the iterator is itself erased.

Pointers and references to objects within a container are also invalidated when iterators are invalidated. A single exception applies for the std::deque class class: it preserves pointers and references to internal objects upon inserts to either its beginning or its end, but it does not preserve iterators.

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double data[5] = { 2.3, 3.7, 1.4, 0.8, 9.6 };
deque<double> d;

transform(data, data+5,
    inserter(d, d.begin()),
    bind2nd(plus<int>(), 41));

Non-compliant Code Example (std::string::data())

In this non-compliant code example, data is to be considered out-of-scope just after the call to replace.

const char *data = example_string.data();
example_string.replace(0, 2, "bb");
char val = data[1];

Compliant Solution (std::string::data())

In this compliant solution, the data array is created after modifications to the example string are complete. The modification makes the code compliant: replace is called before the call to data().

const char *data = example_string.data();
example_string.replace(0, 2, "bb");
data = example_string.data();
char val = data[1];

Risk Assessment

Using invalid iterators yields undefined results.

Bibliography

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