MISRA C:2025 Rule 17.8

R2026b

A function parameter should not be modified

Since R2026b

Description

A function parameter should not be modified ¹ .

Rationale

When you modify a parameter, the function argument corresponding to the parameter is not modified. However, you or another programmer unfamiliar with C can expect by mistake that the argument is also modified when you modify the parameter.

Polyspace Implementation

Polyspace^® reports a violation of this rule when you modify the function parameters in the body of the function. Polyspace does not report a violation of this rule when a function parameter is passed by address as const to another function.

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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Function Parameter Modified

In this example, the rule is violated when the parameter param1 is modified. Polyspace reports a violation. Because param3 is passed to foo as a const, it is not modified. Polyspace does not report a violation.

int input(void);
int foo(const int*);
void func(int param1, int* param2, int param3) {
    
    param1 = input();   /* Non-compliant */
    *param2 = input();  /* Compliant */
    foo(&param3); /*Compliant*/
}

The rule is not violated when a pointer parameter, such as param2 is modified.

Check Information

Group: Functions

Category: Advisory

AGC Category: Disapplied

PQL Name: std.misra_c_2025.R17_8

Version History

Introduced in R2026b