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Marking the function call operator as const is beneficial, but insufficient, because data members with the mutable storage class specifier may still be modified within a const member function.
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Compliant Solution (std::reference_wrapper)
This compliant solution wraps uses std::ref to wrap the predicate in a std::reference_wrapper<T> object, ensuring that copies of the wrapper object all refer to the same underlying predicate object.
| Code Block | ||||
|---|---|---|---|---|
| ||||
#include <algorithm>
#include <functional>
#include <iostream>
#include <iterator>
#include <vector>
class MutablePredicate : public std::unary_function<int, bool> {
size_t timesCalled;
public:
MutablePredicate() : timesCalled(0) {}
bool operator()(const int &) {
return ++timesCalled == 3;
}
};
template <typename Iter>
void print_container(Iter b, Iter e) {
std::cout << "Contains: ";
std::copy(b, e, std::ostream_iterator<decltype(*b)>(std::cout, " "));
std::cout << std::endl;
}
void f() {
std::vector<int> v{0, 1, 2, 3, 4, 5, 6, 7, 8, 9};
print_container(v.begin(), v.end());
MutablePredicate mp;
v.erase(std::remove_if(v.begin(), v.end(), std::ref(mp)), v.end());
print_container(v.begin(), v.end());
} |
The above compliant compliant solution demonstrates using a reference wrapper over a functor object but can similarly be used with a stateful lambda. The code produces the expected results, where only the third element is removed.
| Code Block | ||
|---|---|---|
| ||
Contains: 0 1 2 3 4 5 6 7 8 9 Contains: 0 1 3 4 5 6 7 8 9 |
Compliant Solution (Iterator Arithmetic)
Removing a specific element of a container does not require a predicate function but can instead simply use std::vector::erase(), as in this compliant solution:.
| Code Block | ||||
|---|---|---|---|---|
| ||||
#include <algorithm>
#include <iostream>
#include <iterator>
#include <vector>
template <typename Iter>
void print_container(Iter B, Iter E) {
std::cout << "Contains: ";
std::copy(B, E, std::ostream_iterator<decltype(*B)>(std::cout, " "));
std::cout << std::endl;
}
void f() {
std::vector<int> v{0, 1, 2, 3, 4, 5, 6, 7, 8, 9};
print_container(v.begin(), v.end());
v.erase(v.begin() + 3);
print_container(v.begin(), v.end());
} |
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Using a predicate function object that contains state can produce unexpected values.
Rule | Severity | Likelihood | Remediation Cost | Priority | Level |
|---|---|---|---|---|---|
CTR58-CPP | Low | Likely | High | P3 | L3 |
Automated Detection
Tool | Version | Checker | Description |
|---|
| Helix QAC |
| C++3225, C++3226, C++3227, C++3228, C++3229, C++3230, C++3231, C++3232, C++3233, C++3234 | |||||||
| Parasoft C/C++test |
| CERT_CPP-CTR58-a | Make predicates const pure functions | ||||||
| Polyspace Bug Finder |
| CERT C++: CTR58-CPP | Checks for function object that modifies its state (rule fully covered). |
Related Vulnerabilities
Search for vulnerabilities resulting from the violation of this rule on the CERT website.
Bibliography
| [ISO/IEC 14882-2014] | Subclause 25.1, "General" |
| [Meyers |
| 2001] | Item 39, "Make Predicates Pure Functions" |
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