What happens when realloc fails?

int main()
{
   char *str;

   /* Initial memory allocation */
   str = (char *) malloc(8);
   strcpy(str, "example");
   printf("String = %s,  Address = %u\n", str, str);

   /* Reallocating memory */ 
   str = (char *) realloc(str, 5);
   strcat(str, ".com");
   printf("String = %s,  Address = %u\n", str, str);

   free(str);
   
   return(0);
}

void *temp = realloc(str, 12);
if ( temp != NULL ) {
   str = temp;
   strcat(str, ".com");
} else {
   // no more memory:
   // str is still valid, so do something with it
   // if this were an editor say, you might try to save a recovery file.
   free( str );
}