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In this noncompliant code example, the objects stored in the stdthe std::set have an overloaded operator< overloaded operator< implementation, allowing the objects to be compared with stdwith std::less. However, the comparison operation does not provide a strict weak ordering. Specifically, two sets, x and y, whose i values are both 1, but have differing j values can result in a situation where compwhere comp(x, y) and comp(y, x) are both false, failing the asymmetry requirements.

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Compliant Solution

This compliant solution uses stduses std::tie() to properly implement the strict weak ordering operator< ordering operator< predicate.

#include <iostream>
#include <set>
#include <tuple>
 
class S {
  int i, j;
 
public:
  S(int i, int j) : i(i), j(j) {}
  
  friend bool operator<(const S &lhs, const S &rhs) {
    return std::tie(lhs.i, lhs.j) < std::tie(rhs.i, rhs.j);
  }
  
  friend std::ostream &operator<<(std::ostream &os, const S& o) {
    os << "i: " << o.i << ", j: " << o.j;
    return os;
  }
};

void f() {
  std::set<S> t{S(1, 1), S(1, 2), S(2, 1)};  
  for (auto v : t) {
    std::cout << v << std::endl;
  }
}

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Using an invalid ordering rule can lead to erratic behavior or infinite loops.

Automated Detection

Related Vulnerabilities

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

Related Guidelines

Bibliography

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