MISRA C:2025 Rule 13.3

R2026b

A full expression containing an increment (++) or decrement (--) operator should have no other potential side effects other than that caused by the increment or decrement operator

Since R2026b

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Description

A full expression containing an increment (++) or decrement (--) operator should have no other potential side effects other than that caused by the increment or decrement operator ¹ .

Rationale

The rule is violated if the following happens in the same line of code:

The increment or decrement operator acts on a variable.
Another read or write operation is performed on the variable.

For example, the line y=x++ violates this rule. The ++ and = operator both act on x.

Although the operator precedence rules determine the order of evaluation, placing the ++ and another operator in the same line can reduce the readability of the code.

Troubleshooting

If you expect a rule violation but do not see it, refer to Diagnose Why Coding Standard Violations Do Not Appear as Expected.

Examples

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Increment Operator Used in Expression with Other Side Effects

int input(void);
int choice(void);
int operation(int, int);

int func() {
    int x = input(), y = input(), res;
    int ch = choice();
    if (choice == -1)
        return(x++);               // Noncompliant
    if (choice == 0) {
        res = x++ + y++;           // Noncompliant
        return(res);
    }
    else if (choice == 1) {
        x++;                       // Compliant
        y++;                       // Compliant
        return (x+y);
    }
    else {
        res = operation(x++,y);    // Noncompliant
        return(res);
    }
}

In this example, the rule is violated when the expressions containing the ++ operator have side effects other than that caused by the operator. For example, in the expression return(x++), the other side-effect is the return operation.

Check Information

Group: Side Effects

Category: Advisory

AGC Category: Disapplied

PQL Name: std.misra_c_2025.R13_3

Version History

Introduced in R2026b