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This example tries to remove the 3rd item in a container of widgets by using a predicate that returns true only on its 3rd invocation.
| Code Block | ||||
|---|---|---|---|---|
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class BadPredicate: public unary_function< int, bool> {
public:
BadPredicate() : timesCalled(0) {}
bool operator()(const int&) {
return ++timesCalled == 3;
}
private:
size_t timesCalled;
};
int main () {
vector<int> v;
for (int i = 0; i < 10; i++) v.push_back(i);
cout << "Vector contains:";
for (vector<int>::iterator it = v.begin(); it != v.end(); ++it)
cout << " " << *it;
cout << endl;
v.erase( remove_if( v.begin(), v.end(), BadPredicate()), v.end());
cout << "Vector contains:";
for (vector<int>::iterator it = v.begin(); it != v.end(); ++it)
cout << " " << *it;
cout << endl;
return 0;
}
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A simple way to prevent this behavior is to declare the predicate's operator() to be const.
| Code Block | ||||
|---|---|---|---|---|
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bool operator()(const int&) const {
return ++timesCalled == 3;
}
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The proper way to remove a container element based on position is with iterator arithmetic
| Code Block | ||||
|---|---|---|---|---|
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v.erase( v.begin() + 3); |
Risk Assessment
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