tricky situations with cppcheck

Question

I am facing a situation where i need cppchecks to pass but it gets tricky sometimes. What do you generally do in such circumstances ? For example.

#include<iostream>
using namespace std;
void fun1();
int fun2();
int main()
{
        fun1();
}

void fun1()
{
        int retVal;
        if (-1 == (retVal = fun2()))
        {
                cout <<"Failure. fun2 returned a -1"<< endl;
        }
}

int fun2()
{
        return -1;
}

We usually see code such as the above. cppcheck for the above file would give an output as below -

cppcheck --suppress=redundantAssignment --enable='warning,style,performance,portability' --inline-suppr --language='c++' retval_neverused.cpp Checking retval_neverused.cpp... [retval_neverused.cpp:13]: (style) Variable 'retVal' is assigned a value that is never used.

I don't want to add some dummy line printing retVal just for the sake of cppcheck. Infact it can be a situation where I throw an exception and I don't want the exception to have something trivial as the value of retVal in it.

Answer 1

One common way is with something like this:

#define OK_UNUSED(x) (void)x


void fun1()
{
        int retVal;
        if (-1 == (retVal = fun2()))
        {
                OK_UNUSED (retVal);
                cout <<"Failure. fun2 returned a -1"<< endl;
        }
}

This indicates to humans that retVal is intentionally unused and makes CppCheck think it's used, suppressing the warning.

Note that this macro should not be used if evaluating its parameter has consequences. In that case, you need something fancier like:

#define OK_UNUSED(x) if(false && (x)) ; else (void) 0