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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. |
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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|---|---|---|
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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) {
d.insert(pos++, data[i] + 41);
}
|
Compliant Solution 1
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;
}
|
Compliant Solution 2
Use an algorithmone of the STL algorithms.
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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));
|
Risk Assessment
Using invalid iterators yields undefined results.
Rule | Severity | Likelihood | Remediation Cost | Priority | Level |
|---|---|---|---|---|---|
STL30-C CPP | 3 (high) | 2 (probable) | 1 (high) | P6 | L2 |
References
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\[[Meyers 01|AA. C++ References#Meyers 01]\] Item 43: Prefer algorithm calls to hand-written loops. |
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