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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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Contains: 0 1 2 3 4 5 6 7 8 9  
Contains: 0 1 3 4 6 7 8 9

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This result arises because std::remove_if makes two copies of the predicate before invoking it. The first copy is used to determine the location of the first element in the sequence for which the predicate returns true. The subsequent copy is used for removing other elements in the sequence. This results in the third element (2) and sixth element (5) being removed; two distinct predicate functions are used.

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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.

#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:.

Contains: 0 1 2 3 4 5 6 7 8 9 

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Contains: 0 1 3 4 5 6 7 8 9

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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:.

#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.

Automated Detection

Related Vulnerabilities

Search for vulnerabilities resulting from the violation of this rule on the CERT website.

Bibliography

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