QA·C Help - 2821

	2821	Definite: Arithmetic operation on NULL pointer.

NULL pointers

A definite anomaly has been detected. Examination of the context indicates that this expression will always result in an arithmetic operation involving a null pointer.

The internal representation of a null pointer is implementation-defined and may not necessarily be bitwise 0. A null pointer may be assigned or compared, but any attempt to perform arithmetic operations will result in undefined behaviour.

For example


/*PRQA S 489,508,2017,3205,3408,3673,4600 ++*/
#define NULL (void *)0

void foo(int *q)
{
    int *p;

    if (q == NULL)
    {
        ++q;                /* 2821 */
    }
}

MISRA-C:2004 Rules applicable to message 2821:

Rule 21.1 (Required)

Minimisation of run-time failures shall be ensured by the use of at least one of (a) static analysis tools/techniques; (b) dynamic analysis tools/techniques; (c) explicit coding of checks to handle run-time faults

See also:

2810 Constant: Dereference of NULL pointer.
2811 Definite: Dereference of NULL pointer.
2812 Apparent: Dereference of NULL pointer.
2813 Suspicious: Dereference of NULL pointer.
2814 Possible: Dereference of NULL pointer.
2820 Constant: Arithmetic operation on NULL pointer.
2822 Apparent: Arithmetic operation on NULL pointer.
2823 Suspicious: Arithmetic operation on NULL pointer.
2824 Possible: Arithmetic operation on NULL pointer.

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