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In this noncompliant code sample, the address of local variable str is assigned to the variable p, which has file scope. The assignment itself is legal, but it is illegal for str to go out of scope while p holds its address, as happens at the end of dont_do_this().

const char *p;
void dont_do_this(void) {
    const char str[] = "This will change";
    p = str; /* dangerous */
    /* ... */
}

void innocuous(void) {
    const char str[] = "Surprise, surprise";
}
/* ... */
dont_do_this();
innocuous();
/* p might be pointing to "Surprise, surprise" */

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In this compliant solution, p is declared with the same scope as str, preventing p from taking on an indeterminate value outside of this_is_OK().

void this_is_OK(void) {
    const char str[] = "Everything OK";
    const char *p = str;
    /* ... */
}
/* p is inaccessible outside the scope of string str */

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If it is necessary for p to be defined with file scope, but str with a more limited scope, then p can be set to NULL before str is destroyed. This prevents p from taking on an indeterminate value, although any references to p must check for NULL.

const char *p;
void is_this_OK(void) {
    const char str[] = "Everything OK?";
    p = str;
    /* ... */
    p = NULL;
}

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In this noncompliant code sample, the function init_array() returns a pointer to a local stack variable, which could be accessed by the caller.

char *init_array(void) {
   char array[10];
   /* Initialize array */
   return array;
}

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The solution, in this case, depends on the intent of the programmer. If the intent is to modify the value of array and have that modification persist outside of the scope of init_array(), the desired behavior can be achieved by declaring array elsewhere and passing it as an argument to init_array().

void init_array(char array[]) {
   /* Initialize array */
   return;
}

int main(int argc, char *argv[]) {
   char array[10];
   init_array(array);
   /* ... */
   return 0;
}

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In this noncompliant code sample, the function squirrel_away() stores a pointer to local stack variable local into a location pointed to by function parameter ptr_param. Since it an be assumed that the pointer variable to which ptr_param points remains alive upon squirrel_away()'s return, it is illegal for local to go out of scope.

void squirrel_away(char **ptr_param) {
   char local[10];
   /* Initialize array */
   *ptr_param = local;
}

void rodent() {
  char *ptr;
  squirrel_away(&ptr);
  /* ptr is live but invalid here */
}

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