QA·C Help - 2822

	2822	Apparent: Arithmetic operation on NULL pointer.

NULL pointers

An apparent anomaly has been detected. Preceding operations imply that this pointer value will sometimes be null.

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 on it will result in undefined behaviour.

For example, in the code shown below, the expression in the "if" statement implies that the value of q is expected to be NULL - sometimes, and so it should not be incremented. Of course, if the value of q is never actually NULL, the increment operation will always be valid; but this would imply that the "if" statement is redundant and any code contained in the "if" block is also redundant.


/*PRQA S 489,508,509,2017,3205,3408,3673,4600 ++*/
#define NULL (void *)0

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

    if (q == NULL)
    {
    }

    ++q;                    /* 2822  */
}

MISRA-C:2004 Rules applicable to message 2822:

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.
2821 Definite: Arithmetic operation on NULL pointer.
2823 Suspicious: Arithmetic operation on NULL pointer.
2824 Possible: Arithmetic operation on NULL pointer.

QA·C Source Code Analyser 8.1
MISRA-C:2004 Compliance Module 3.2
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