Do not dereference invalid pointers

Attempting to dereference an invalid pointer results in undefined program behavior, typically abnormal program termination. Given this, invalid pointers should not be dereferenced.

Non-compliant Example

In this example, input_string is copied into dynamically allocated memory referenced by str. If malloc() }} fails, it returns an invalid (null) pointer that is assigned to {{str. When str is dereferenced in strcpy(), the program behave in an unpredictable manner.

char *str = malloc(strlen(input_string)+1);
strcpy(str, input_string); /* What if malloc() fails? */

Compliant Solution

To correct this error, check the pointer returned by malloc() to ensure that it is not null. In addition to ths rule, this should be done in accordance with rule MEM32-C. Detect and handle critical memory allocation errors.

char *str = malloc(strlen(input_string)+1);
if (str == NULL) {
  /* Handle Allocation Error */
}
strcpy(str, input_string);

Priority and Level

Dereferencing null pointers typically results in a denial of service condition.

References

• ISO/IEC 9899-1999 6.3.2.3 Pointers