With C++ how do I Pass a value from a void function?

Question

I have two C++ functions in a class:

void Attribute::setIndex(int inIndex) {
    if (inIndex < 0) {
        index = 0;
    }
    else if (inIndex >= MAX_NUM_ATTRIBUTES) {
        index = MAX_NUM_ATTRIBUTES - 1;
    }
    else {
        index = inIndex;
    }
}

and

int Attribute::getValueWithinRange(int value) {
    value = setIndex(value);
    return value;
}

The second function is supposed to use setIndex to set 'value' to the correct number and return it. However, since the first function is a void function, i cannot simply pas the value in the way i did above. Should i do pass by reference or are there any suggestions? Thank you very much.

Change `setIndex` to return a value? Or maybe there's a matching `getIndex()` function you can use? — Jonathan Potter, Nov 09 '15 at 02:37
There is a getIndex function that simply returns index. Should i just use it in getValueWithinRange instead of setIndex? — fishforever, Nov 09 '15 at 02:40
This is very basic stuff, I recommend you read a good introductory C++ book http://stackoverflow.com/q/388242/873025 — Felix Glas, Nov 09 '15 at 02:42
change the latter function to `setIndex(value); return getIndex();` — M.M, Nov 09 '15 at 02:59

score 1 · Accepted Answer · edited Nov 09 '15 at 04:15

I would like just to note, that if you are learning C++, you should try to learn model cases first, sometimes rushing examples is not the best way, but there we go:

Change the setIndex to return int, my favorite;

int Attribute::setIndex(int inIndex)
{
    if (inIndex < 0)
    {
        index = 0;
    }
    else if (inIndex >= MAX_NUM_ATTRIBUTES)
    {
        index = MAX_NUM_ATTRIBUTES - 1;
    }
    else
    {
        index = inIndex;
    }

    return index;
}


int Attribute::getValueWithinRange(int value)
{
    value = setIndex(value);
    return value;
}

Change the getValueWithinRange to return index, both methods are in one class, they share the access to index;

int Attribute::getValueWithinRange(int value)
{
    setIndex(value);
    return index;
}

Giving it reference would work, but you can not set reference to null unless using a trick and it would require unnecessarily another method, so pointer makes it less messy:

int Attribute::setIndex(int inIndex, int* ret_index = nullptr)
{
    if (inIndex < 0)
    {
        index = 0;
    }
    else if (inIndex >= MAX_NUM_ATTRIBUTES)
    {
        index = MAX_NUM_ATTRIBUTES - 1;
    }
    else
    {
        index = inIndex;
    } 

    if (ret_index != nullptr) *ret_index = index;

    return index;
}


int Attribute::getValueWithinRange(int value)
{
    int retvalue;
    setIndex(value); // use it like this when returning value is not needed
    setIndex(value, &retvalue);

    return retvalue;
}

I prefer you to correct the indentation of your code examples to make it more readable. — Joe, Nov 09 '15 at 03:00

With C++ how do I Pass a value from a void function?

1 Answers1