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Based on the preceding effects, the following table distinguishes three kinds of exception safety guarantees from most to least desired.

Code that guarantees strong exception safety also guarantees basic exception safety.

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In this compliant solution, the copy assignment operator provides the strong exception safety guarantee. The function allocates new storage for the copy before changing the state of the object. Only after the allocation succeeds does the function proceed to change the state of the object. In addition, by copying the array to the newly allocated storage before deallocating the existing array, the function avoids the test for self-assignment, which improves the performance of the code in the common case [Sutter 2004].

#include <cstring>
 
class IntArray {
  int *array;
  std::size_t nElems;
public:
  // ...

  ~IntArray() {
    delete[] array;
  }

  IntArray(const IntArray& that); // nontrivial copy constructor

  IntArray& operator=(const IntArray &rhs) {
    int *tmp = nullptr;
    if (rhs.nElems) {
      tmp = new int[rhs.nElems];
      std::memcpy(tmp, rhs.array, rhs.nElems * sizeof(*array));
    }
    delete[] array;
    array = tmp;
    nElems = rhs.nElems;
    return *this;
  }

  // ...
};

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Code that is not exception safe typically leads to resource leaks, causes the program to be left in an inconsistent or unexpected state, and ultimately results in undefined behavior at some point after the first exception is thrown.

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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