MISRA C++:2008 Rule 0-1-11

There shall be no unused parameters (named or unnamed) in nonvirtual functions

Description

There shall be no unused parameters (named or unnamed) in nonvirtual functions. ¹

Rationale

Unused parameters often indicate later design changes. You perhaps removed all uses of a specific parameter but forgot to remove the parameter from the parameter list.

Unused parameters constitute an unnecessary overhead. You can also inadvertently call the function with a different number of arguments causing a parameter mismatch.

Polyspace Implementation

The checker flags a function that has unused named parameters unless the function body is empty.

Additional Message in Report

Function funcName has unused parameters.

Troubleshooting

If you expect a rule violation but Polyspace^® does not report it, see Diagnose Why Coding Standard Violations Do Not Appear as Expected.

Examples

Unused Parameters

typedef int (*callbackFn) (int a, int b);

int callback_1 (int a, int b) { //Compliant
    return a+b;
}

int callback_2 (int a, int b) { //Noncompliant
    return a;
}

int callback_3 (int, int b) { //Compliant - flagged by Polyspace
    return b;
}

int getCallbackNumber();
int getInput();

void main() {
    callbackFn ptrFn;
    int n = getCallbackNumber();
    int x = getInput(), y = getInput();
    switch(n) {
        case 0: ptrFn = &callback_1; break;
        case 1: ptrFn = &callback_2; break;
        default: ptrFn = &callback_3; break;
    }
    
    (*ptrFn)(x,y);
}

In this example, the three functions callback_1, callback_2 and callback_3 are used as callback functions. One of the three functions is called via a function pointer depending on a value obtained at run time.

• Function callback_1 uses all its parameters and does not violate the rule.

• Function callback_2 does not use its parameter a and violates this rule.

• Function callback_3 also does not use its first parameter but it does not violate the rule because the parameter is unnamed. However, Polyspace flags the unused parameter as a rule violation. If you see a violation of this kind, justify the violation with comments. See Address Polyspace Results Through Bug Fixes or Justifications.

Check Information

Group: Language Independent Issues

Category: Required

Version History

Introduced in R2016b