Sanity check of the given function in C++

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Hi All,
I was asked following question in an interview and was asked that it is having sanity check issues. Could anyone please help me in this:

//following function should increment the value of x

C++

void increment(int x)
{
    x++;
    return; 
}

Regards

What I have tried:

I have asked to change copy by value to pass by reference by it was still giving error.

Posted 28-Apr-19 19:49pm

Rahul@puna

Updated 28-Apr-19 20:22pm

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Christian Graus 29-Apr-19 1:52am

This code should not give an error. If you pass by reference, then x will be incremented in the calling code. If you changed it and got an error, give us the new code and the error if you're stuck

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Christian Graus · Answer 1 · 2019-04-28T19:52:00

Solution 1

This code should not give an error. If you pass by reference, then x will be incremented in the calling code. If you changed it and got an error, give us the new code and the error if you're stuck

Posted 28-Apr-19 19:52pm

Christian Graus

Comments

Rahul@puna 29-Apr-19 1:56am

There was no specific error as such. I was doing this thing on a interview portal and their after checking with reference , it is compiling ok but giving some sanity error. that i am trying to figure out. what could be missing here.

Christian Graus 29-Apr-19 1:59am

This will do nothing. It increments a local variable and returns. If you make it a ref, then it will pass by reference and increment the variable in the calling code

You could also pass in a pointer and get the same result. You'd have to dereference the pointer to increment it though.

Rahul@puna 29-Apr-19 2:01am

Yes actually I have updated the code. Following is that that i have updated to but still it was giving sanity check error.

void increment(int& x)
{
x++;
return;
}

Christian Graus 29-Apr-19 2:02am

What is a 'sanity check error'?

Rahul@puna 29-Apr-19 2:04am

not sure of that, it's in their tool. May be they are doing some validation of the function and then giving output on the basis of that. I need to figure out what could be wrong with this function in any case.

Christian Graus 29-Apr-19 2:05am

Nothing. It's doing exactly what they asked. The return statement is superfluous, you could remove it. That's the only improvement I see

Rahul@puna 29-Apr-19 2:06am

yes that might be.

Christian Graus 29-Apr-19 2:07am

If they wrote the tool, a bug in the tool is not an impossible problem to have

KarstenK · Answer 2 · 2019-04-28T20:23:00

Solution 2

One issue in this function can be that it has NO EXTERNAL EFFECTS. The input x is created on the stack, locally modified and than destroyed.

So the function only modies the local x and nothing more. You can change this behaviour with the &-operator, as mentioned before.

Posted 28-Apr-19 20:23pm

KarstenK

Comments

Christian Graus 29-Apr-19 2:24am

That was the point here. he was given a function that did nothing and asked to make it work