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const errno_t ESOMETHINGREALLYBAD = 1;

void g(errno_t* err) {
  if (err == NULL) {
    /* handle nullNULL pointer */
  }
  /* ... */
  if (something_really_bad_happens) {
    *err = ESOMETHINGREALLYBAD;
  } else {
    /* ... */
    *err = 0;
  }
}

void f(errno_t* err) {
  if (err == NULL) {
    /* handle nullNULL pointer */
  }
  g(err);
  if (*err == 0) {
    /* ... do the rest of f ... */
  }
  return 0;
}

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• A return status can only be returned if the caller provides a valid pointer to an object of type errno_t. If this argument is nullNULL, there is no way to indicate this error.
• Source code becomes even larger, due to the possibilities of receiving a null NULL pointer.
• All error indicators must be checked after calling functions.
• Any function that allocates resources must ensure they are freed incases where errors occur.
• Unlike return values, static analysis tools generally do not diagnose a failure to check error indicators passed as argument pointers.

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