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MISRA C:2023 Rule 13.6

The operand of the sizeof operator shall not contain any expression which has potential side effects

Since R2024a

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Description

Rule Definition

The operand of the sizeof operator shall not contain any expression which has potential side effects.

Rationale

The argument of a sizeof operator is usually not evaluated at run time. If the argument is an expression, you might wrongly expect that the expression is evaluated.

Polyspace Implementation

The rule checker reports a violation if the operand of a sizeof operator has side effects that persist beyond the sizeof expression. For instance, if the sizeof operator increments a global variable, the rule checker reports a violation.

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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#include <stddef.h>
int x;
int y[40];
struct S {
    int a;
    int b;
};
struct S myStruct;

void main() {
    size_t sizeOfType;
    sizeOfType = sizeof(x);         /* Compliant */
    sizeOfType = sizeof(y);         /* Compliant */
    sizeOfType = sizeof(myStruct);  /* Compliant */
    sizeOfType = sizeof(x++);       /* Non-compliant */
}

In this example, the rule is violated when the expression x++ is used as argument of sizeof operator.

Check Information

Group: Side Effects
Category: Required
AGC Category: Required

Version History

Introduced in R2024a

See Also

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