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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. Consequently, the values of existing iterators are invalidated \[[Kalev 99|AA. C++ References#Kalev 99]\]. Using invalid iterators yields undefined results. (This problem is also discussed in [DAN33-C|DAN33-C. Do not use invalid iterators].) |
Non-Compliant Code Example
In this example, the iterator pos is invalidated after the call to insert, and subsequent loop iterations have undefined behavior.
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Update pos each time insert is called to keep the iterators valid, and then increment it:
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double data[5] = { 2.3, 3.7, 1.4, 0.8, 9.6 };
deque<double> d;
deque<double>::iterator pos = d.begin();
for (size_t i = 0; i < 5; ++i) {
pos = d.insert(pos, data[i] + 41);
++pos;
}
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