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MISRA C:2012 Rule 17.8

A function parameter should not be modified

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Description

Rule Definition

A function parameter should not be modified.

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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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: Readability

Version History

Introduced in R2015b

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See Also

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