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#include <stdio.h>

struct X { int a[6]; };

struct X addressee(void) {
  struct X result = { { 1, 2, 3, 4, 5, 6 } };
  return result;
}

int main(void) {
  struct X my_x = addressee();
  printf("%x", ++(my_x.a[0]));
  return 0;
}

Noncompliant Code Example

This noncompliant code example attempts to save a pointer to an array that is part of a struct that is returned by a function call. Consequently, the array has temporary lifetime, and using the pointer to it outside of the full expression is undefined behavior in both C99 and C11.

#include <stdio.h>

struct X { int a[6]; };

struct X addressee(void) {
  struct X result = { { 1, 2, 3, 4, 5, 6 } };
  return result;
}

int main(void) {
  int *my_a = addressee().a;
  printf("%x", my_a[0]);
  return 0;
}

Compliant Solution

This compliant solution stores the structure returned by the call to addressee() as my_x before saving a pointer to its array member. When the pointer is used, its lifetime is no longer temporary but matches the lifetime of the block in main().

#include <stdio.h>

struct X { int a[6]; };

struct X addressee(void) {
  struct X result = { { 1, 2, 3, 4, 5, 6 } };
  return result;
}

int main(void) {
  struct X my_x = addressee();
  int *my_a = my_x.a;
  printf("%x", my_a[0]);
  return 0;
}

Risk Assessment

Attempting to modify an array or access it after its lifetime expires may result in erroneous program behavior.

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