QA·C Help - 3389

	3389	Extra parentheses recommended to clarify the ordering of a % operator and another arithmetic operator (* / % + -).

Readability

The order in which operators are processed in this expression is not sufficiently clear and so additional parentheses are recommended. In the absence of parentheses, the sequence is determined by rules of precedence and associativity.

In this expression, the ordering of two operations needs to be clarified; one is a % operator and the other is a +, -, * or / operator or another %. Add parentheses to make it clear which operator is evaluated first.

For example:


/*PRQA S 584,2017,3103,3198,3199,3203,3401,3408,3447 ++*/

extern int a;
extern int b;
extern int c;


extern void foo(void)
{
    int r;

    r = a + b % c;        /* Message 3389 + 3390 */
    r = a + (b % c);      /* OK                  */

    r = a % b % c;        /* Message 3389 + 3390 */
    r = (a % b) % c;      /* OK                  */

    r = a % b * c;        /* Message 3389 + 3390 */
    r = (a % b) * c;      /* OK                  */

    r = a * b % c;        /* Message 3389 + 3390 */
    r = (a * b) % c;      /* OK                  */



}

MISRA-C:2004 Rules applicable to message 3389:

Rule 12.1 (Advisory)

Limited dependence should be placed on C's operator precedence rules in expressions.

See also:

3391 Extra parentheses recommended. A conditional operation is the operand of another conditional operator.
3392 Extra parentheses recommended. A shift, relational or equality operation is the operand of a second identical operator.
3393 Extra parentheses recommended. An arithmetic operation (* / + -) is the operand of a different operator with the same precedence.
3394 Extra parentheses recommended. A shift, relational or equality operation is the operand of a different operator with the same precedence.
3395 Extra parentheses recommended. A * or / operation is the operand of a + or - operator.
3396 Extra parentheses recommended. A binary operation is the operand of a conditional operator.
3397 Extra parentheses recommended. A binary operation is the operand of a binary operator with different precedence.

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MISRA-C:2004 Compliance Module 3.2
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